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fp@369: %
fp@369: %  IgH EtherCAT Master Documentation
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fp@369: %  $Id$
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fp@369: \documentclass[a4paper,12pt,BCOR6mm,bibtotoc,idxtotoc]{scrbook}
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fp@369: \usepackage[refpage]{nomencl}
fp@369: \usepackage{listings}
fp@369: \usepackage{svn}
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fp@369: \usepackage{url}
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fp@369: \lstset{basicstyle=\ttfamily\small,numberstyle=\tiny,aboveskip=4mm,
fp@369:   belowskip=2mm,gobble=2,escapechar=`}
fp@369: \renewcommand\lstlistlistingname{List of Listings}
fp@369: 
fp@369: \renewcommand\nomname{Glossary}
fp@369: 
fp@369: \newcommand{\IgH}{\raisebox{-0.7667ex}
fp@369:   {\includegraphics[height=2.2ex]{images/ighsign}}}
fp@369: 
fp@369: \SVN $Date$
fp@369: \SVN $Revision$
fp@369: 
fp@369: \makeindex
fp@369: \makeglossary
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \begin{document}
fp@369: 
fp@369: \pagenumbering{roman}
fp@369: \pagestyle{empty}
fp@369: 
fp@369: \begin{titlepage}
fp@369:   \begin{center}
fp@369:     \rule{\textwidth}{1.5mm}
fp@369: 
fp@369:     {\Huge\bf IgH \includegraphics[height=2.4ex]{images/ethercat}
fp@369:       Master 1.1\\[1ex]
fp@369:       Documentation}
fp@369: 
fp@369:     \vspace{1ex}
fp@369:     \rule{\textwidth}{1.5mm}
fp@369: 
fp@369:     \vspace{\fill}
fp@369:     {\Large Florian Pose, \url{fp@igh-essen.com}\\[1ex]
fp@369:       Ingenieurgemeinschaft \IgH}
fp@369: 
fp@369:     \vspace{\fill}
fp@369:     {\Large Essen, \SVNDate\\[1ex]
fp@369:       Revision \SVNRevision}
fp@369:   \end{center}
fp@369: \end{titlepage}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \tableofcontents
fp@369: \listoftables
fp@369: \listoffigures
fp@369: \lstlistoflistings
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \newpage
fp@369: \pagestyle{scrheadings}
fp@369: 
fp@369: \section*{Conventions}
fp@369: \addcontentsline{toc}{section}{Conventions}
fp@369: \markleft{Conventions}
fp@369: 
fp@369: The following typographic conventions are used:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item \textit{Italic face} is used for newly introduced terms, file
fp@369:   names, parameter names and in-text source code elements.
fp@369: \item \texttt{Typewriter face} is used for code examples and
fp@369:   command line output.
fp@369: \item \texttt{\textbf{Bold typewriter face}} is used for user input in
fp@369:   command lines.
fp@369: \end{itemize}
fp@369: 
fp@369: Data values and addresses are specified as hexadecimal values with the
fp@369: prefix 0x. Example: 0x88A4. Unless otherwise noted, address values are
fp@369: specified as byte addresses.
fp@369: 
fp@369: Concerning bit operations, the phrase ``setting a bit'', stands for
fp@369: setting the bit to $1$, ``clearing a bit'' means setting it to $0$,
fp@369: respectively.
fp@369: 
fp@369: Function names are always printed with parentheses, but without
fp@369: parameters. So, if a function \textit{ecrt\_request\_master()} has
fp@369: empty parentheses, this does not mean, that it has no parameters.
fp@369: 
fp@369: If shell commands have to be entered, this is marked by a prompt:
fp@369: 
fp@369: \begin{lstlisting}[gobble=2]
fp@369:   host>
fp@369: \end{lstlisting}
fp@369: 
fp@369: Further, if a shell command has to be entered as the superuser, the
fp@369: prompt ends with a mesh:
fp@369: 
fp@369: \begin{lstlisting}[gobble=2]
fp@369:   host#
fp@369: \end{lstlisting}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \chapter{The IgH EtherCAT Master}
fp@369: \label{chapter:master}
fp@369: \pagenumbering{arabic}
fp@369: 
fp@369: This section will first introduce the master's general features and
fp@369: the concepts used for master development and will then explain the
fp@369: master's general architecture and offer details of the different
fp@369: modules. In addition, it will cover state machine definitions, mailbox
fp@369: protocol implementation and the user space interface. The last section
fp@369: will deal with timing aspects.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Feature Summary}
fp@369: \label{sec:summary}
fp@369: \index{Master!Features}
fp@369: 
fp@369: The list below gives a short summary of the features of the
fp@369: implemented EtherCAT master.
fp@369: 
fp@369: \begin{itemize}
fp@369: \item The master runs as a kernel module for Linux 2.6.
fp@369: \item It comes with EtherCAT-capable network driver for RealTek
fp@369:   RTL8139 (and compatible) network interface cards.
fp@369:   \begin{itemize}
fp@369:   \item The Ethernet hardware is operated without interrupts.
fp@369:   \item Drivers for additional Ethernet hardware can easily be
fp@369:     implemented due to a common device interface provided by the
fp@369:     master.
fp@369:   \end{itemize}
fp@369: \item The master module supports multiple EtherCAT masters on one
fp@369:   machine.
fp@369: \item The master code supports any Linux realtime extension through
fp@369:   its independent architecture.
fp@369:   \begin{itemize}
fp@369:   \item RTAI\nomenclature{RTAI}{RealTime Application Interface},
fp@369:     ADEOS\nomenclature{ADEOS}{Adaptive Domain Environment for
fp@369:       Operating Systems}, etc.
fp@369:   \item It runs well even without realtime extensions.
fp@369:   \end{itemize}
fp@369: \item Common ``realtime interface'' for modules, that want to use
fp@369:   EtherCAT functionality.
fp@369:   \begin{itemize}
fp@369:   \item Synchronous and asynchronous sending and receiving of frames
fp@369:     is supported.
fp@369:   \item Avoidance of unnecessary copy operations for process data.
fp@369:   \end{itemize}
fp@369: \item \textit{Domains} are introduced, to allow grouping of process
fp@369:   data objects.
fp@369:   \begin{itemize}
fp@369:   \item Handling of multiple domains with different sampling rates.
fp@369:   \item Automatic calculation of process data mapping, FMMU and sync manager
fp@369:     configuration within each domain.
fp@369:   \end{itemize}
fp@369: \item Communication through serveral finite state machines.
fp@369:   \begin{itemize}
fp@369:   \item Bus monitoring possible during realtime operation.
fp@369:   \item Automatic reconfiguration of slaves on bus power failure
fp@369:     during realtime operation.
fp@369:   \item Controlling of single slaves during realtime operation.
fp@369:   \end{itemize}
fp@369: \item Master idle mode.
fp@369:   \begin{itemize}
fp@369:   \item Automatic scanning of slaves upon topology changes.
fp@369:   \item Bus visualisation and EoE processing without a realtime module
fp@369:     connected.
fp@369:   \end{itemize}
fp@369: \item Implementation of the CANopen-over-EtherCAT (CoE) protocol.
fp@369:   \begin{itemize}
fp@369:   \item Configuration of CoE-capable slaves via SDO interface.
fp@369:   \end{itemize}
fp@369: \item Implementation of the Ethernet-over-EtherCAT (EoE) protocol.
fp@369:   \begin{itemize}
fp@369:   \item Each master creates virtual network devices that are
fp@369:     automatically coupled to EoE-cap\-able slaves found.
fp@369:   \item This implementation natively supports either a switched or a
fp@369:     routed EoE network architecture.
fp@369:   \end{itemize}
fp@369: \item User space interface via the System Filesystem
fp@369:   (Sysfs)\nomenclature{Sysfs}{System Filesystem}.
fp@369:   \begin{itemize}
fp@369:   \item User space tool for bus visualisation.
fp@369:   \item Slave E$^2$PROM image reading and writing.
fp@369:   \end{itemize}
fp@369: \item Seamless system integration though LSB\nomenclature{LSB}{Linux
fp@369:     Standard Base} compliance.
fp@369:   \begin{itemize}
fp@369:   \item Master and network device configuration via Sysconfig files.
fp@369:   \item Linux Standard Base compatible init script for master control.
fp@369:   \end{itemize}
fp@369: \item Virtual read-only network interface for monitoring and debugging
fp@369:   purposes.
fp@369: \end{itemize}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{License}
fp@369: \label{sec:license}
fp@369: 
fp@369: The master code is released under the terms and conditions of the GNU
fp@369: General Public License\index{GPL} \cite{gpl} (version 2). Other
fp@369: developers, that want to use EtherCAT with Linux systems, are invited
fp@369: to use the master code or even participate on development.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{General Master Architecture}
fp@369: \label{sec:masterarch}
fp@369: \index{Master!Architecture}
fp@369: 
fp@369: The EtherCAT master is integrated into the Linux 2.6 kernel. This was
fp@369: an early design decision, which has been made for serveral reasons:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item Kernel code has significantly better realtime characteristics,
fp@369:   i.~e. less jitter than user space code. It was foreseeable, that a
fp@369:   fieldbus master has a lot of cyclic work to do. Cyclic work is
fp@369:   usually triggered by timer interrupts inside the kernel. The
fp@369:   execution delay of a function that processes timer interrupts is
fp@369:   less, when it resides in kernel space, because there is no need of
fp@369:   time-consuming context switches to a user space process.
fp@369: \item It was also foreseeable, that the master code has to directly
fp@369:   communicate with the Ethernet hardware. This has to be done in the
fp@369:   kernel anyway (through network device drivers), which is one more
fp@369:   reason for the master code being in kernel space.
fp@369: \end{itemize}
fp@369: 
fp@369: A general overview of the master architecture can be seen in
fp@369: figure~\ref{fig:masterarch}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/masterarch}
fp@369:   \caption{Master architecture}
fp@369:   \label{fig:masterarch}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Master Module}
fp@369: \index{Master module}
fp@369: 
fp@369: The EtherCAT master mainly consists of the master module, containing
fp@369: one or more EtherCAT masters (section~\ref{sec:mastermod}), the
fp@369: ``Device Interface'' (section~\ref{sec:ecdev}) and the ``Realtime
fp@369: Interface'' (section~\ref{sec:ecrt}).
fp@369: 
fp@369: \paragraph{Device Modules}
fp@369: \index{Device modules}
fp@369: 
fp@369: Furthermore there are EtherCAT-capable network device driver
fp@369: modules\index{Device modules}, that connect to the EtherCAT master via
fp@369: the device interface. These modified network drivers can handle both
fp@369: network devices used for EtherCAT operation and ``normal'' Ethernet
fp@369: devices. The common case is, that the master module offers a single
fp@369: EtherCAT master: An EtherCAT-capable network device driver module
fp@369: connects one network device to this master, that is now able to send
fp@369: and receive EtherCAT frames, while all other network devices handled
fp@369: by the network driver get connected to the kernel's network stack as
fp@369: usual.
fp@369: 
fp@369: \paragraph{Realtime Modules}
fp@369: 
fp@369: A ``realtime module''\index{Realtime module} is a kernel module, that
fp@369: uses the EtherCAT master for cyclic exchange of process data with
fp@369: EtherCAT slaves. Realtime modules are not part of the EtherCAT master
fp@369: code\footnote{Although there are serveral examples provided in the
fp@369:   \textit{examples} directory, see chapter~\ref{chapter:usage} for
fp@369:   more information}, so anybody wanting to use the master has to write
fp@369: one. A realtime module can ``request'' a master through the realtime
fp@369: interface. If this succeeds, the module has the control over the
fp@369: master. It can now configure slaves and set up a process data image
fp@369: (see section~\ref{sec:processdata}) for cyclic exchange. This cyclic
fp@369: code has to be provided by the realtime module, so it is in hands of
fp@369: the developer, which mechanism to use for this. Moreover he has to
fp@369: decide, whether or not using a Linux realtime extension.
fp@369: 
fp@369: \paragraph{Why ``Realtime'' Module?}
fp@369: 
fp@369: The name shall not imply, that a linux realtime extension is
fp@369: mandatory: The master runs well even without realtime extensions, as
fp@369: section~\ref{sec:mini} shows. However, the code using the master is
fp@369: time-critical, because process data IO has to be done in cyclic work.
fp@369: Some EtherCAT slaves support watchdog units, that stop driving the
fp@369: outputs when process data was not exchanged for some time. So the
fp@369: names ``realtime interface'' and ``realtime module'' are quite
fp@369: appropriate.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Handling of Process Data}
fp@369: \label{sec:processdata}
fp@369: 
fp@369: \paragraph{Process Data Image}
fp@369: \index{Process data}
fp@369: 
fp@369: The slaves offer their inputs and outputs by presenting the master
fp@369: so-called ``Process Data Objects'' (PDOs\index{PDO}). The available
fp@369: PDOs can be determined by reading out the slave's TXPDO and RXPDO
fp@369: E$^2$PROM categories. The realtime module can register the PDOs for
fp@369: data exchange during cyclic operation. The sum of all registered PDOs
fp@369: defines the ``process data image'', which is exchanged via the
fp@369: ``Logical ReadWrite'' datagrams introduced
fp@369: in~\cite[section~5.4.2.4]{dlspec}.
fp@369: 
fp@369: \paragraph{Process Data Domains}
fp@369: \index{Domain}
fp@369: 
fp@369: The process data image can be easily managed by creating co-called
fp@369: ``domains'', which group PDOs and allocate the datagrams needed to
fp@369: exchange them. Domains are mandatory for process data exchange, so
fp@369: there has to be at least one. They were introduced for the following
fp@369: reasons:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item The maximum size of a ``Logical ReadWrite'' datagram is limited
fp@369:   due to the limited size of an Ethernet frame: The maximum data size
fp@369:   is the Ethernet data field size minus the EtherCAT frame header,
fp@369:   EtherCAT datagram header and EtherCAT datagram footer: $1500 - 2 -
fp@369:   12 - 2 = 1484$ octets. If the size of the process data image exceeds
fp@369:   this limit, multiple frames have to be sent, and the image has to be
fp@369:   partitioned for the use of multiple datagrams. A domain manages this
fp@369:   automatically.
fp@369: \item Not every PDO has to be exchanged with the same frequency: The
fp@369:   values of PDOs can vary slowly over time (for example temperature
fp@369:   values), so exchanging them with a high frequency would just waste
fp@369:   bus bandwidth. For this reason, multiple domains can be created, to
fp@369:   group different PDOs and so allow separate exchange.
fp@369: \end{itemize}
fp@369: 
fp@369: There is no upper limit for the number of domains, but each domain
fp@369: occupies one FMMU in each slave involved, so the maximum number of
fp@369: domains is also limited by the slaves' capabilities.
fp@369: 
fp@369: \paragraph{FMMU Configuration}
fp@369: \index{FMMU!Configuration}
fp@369: 
fp@369: A realtime module can register PDOs for process data exchange. Every
fp@369: PDO is part of a memory area in the slave's physical memory, that is
fp@369: protected by a sync manager \cite[section~6.7]{dlspec} for
fp@369: synchronized access. In order to make a sync manager react on a
fp@369: datagram accessing its memory, it is necessary to access the last byte
fp@369: covered by the sync manager. Otherwise the sync manager will not react
fp@369: on the datagram and no data will be exchanged. That is why the whole
fp@369: synchronized memory area has to be included into the process data
fp@369: image: For example, if a certain PDO of a slave is registered for
fp@369: exchange with a certain domain, one FMMU will be configured to map the
fp@369: complete sync-manager-protected memory, the PDO resides in. If a
fp@369: second PDO of the same slave is registered for process data exchange
fp@369: within the same domain, and this PDO resides in the same
fp@369: sync-manager-protected memory as the first PDO, the FMMU configuration
fp@369: is not touched, because the appropriate memory is already part of the
fp@369: domain's process data image.  If the second PDO belongs to another
fp@369: sync-manager-protected area, this complete area is also included into
fp@369: the domains process data image. See figure~\ref{fig:fmmus} for an
fp@369: overview, how FMMU's are configured to map physical memory to logical
fp@369: process data images.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=\textwidth]{images/fmmus}
fp@369:   \caption{FMMU configuration for serveral domains}
fp@369:   \label{fig:fmmus}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Process Data Pointers}
fp@369: 
fp@369: The figure also demonstrates the way, the realtime module can access the
fp@369: exchanged process data: At PDO registration, the realtime module has
fp@369: to provide the address of a process data pointer. Upon calculation of
fp@369: the domain image and allocation of process data memory, this pointer
fp@369: is redirected to the appropriate location inside the domain's process
fp@369: data memory and can later be easily dereferenced by the module code.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Operation Modes}
fp@369: \index{Master modes}
fp@369: 
fp@369: The EtherCAT master has serveral modes of operation:
fp@369: 
fp@369: \begin{description}
fp@369: \item[Orphaned Mode] This mode takes effect, when the master has no
fp@369:   EtherCAT-capable network device connected. No bus communication is
fp@369:   possible, so this mode is not of further interest.
fp@369: \item[Idle Mode]\index{Idle mode} takes effect when the master is
fp@369:   unused (i.~e. there is no realtime module, that reserved the
fp@369:   master). In this case, the master has the ability to scan the bus by
fp@369:   itsself and generously allow bus access from user space.  This mode
fp@369:   is meant for maintenance and visualisation.
fp@369: \item[Operation Mode]\index{Operation mode} The master is reserved for
fp@369:   exclusive access by a realtime module. In this mode, the master is
fp@369:   adjusted for availability and monitoring. Access from user space is
fp@369:   very restrictive and mostly limited to reading direction.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: Figure~\ref{fig:modes} shows the three modes and the possible mode
fp@369: transitions.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/modes}
fp@369:   \caption{Master modes and transitions}
fp@369:   \label{fig:modes}
fp@369: \end{figure}
fp@369: 
fp@369: \subsubsection{Idle Mode}
fp@369: \index{Idle mode}
fp@369: 
fp@369: The master enters idle mode upon connection of a device module (see
fp@369: section~\ref{sec:device}) or releasing by a realtime module. The
fp@369: master owns a kernel workqueue and a suitable work structure, which is
fp@369: used to cyclically process the ``Idle state machine'' (see
fp@369: section~\ref{sec:fsm-idle}). This state machine automatically scans
fp@369: the bus for slaves (and re-scans upon topology changes), configures
fp@369: slaves for idle operation and executes pending operations from the
fp@369: user space interface (for example E$^2$PROM writing). On device
fp@369: disconnection or realtime request, the idle mode is stopped by
fp@369: cancelling the work and flushing the workqueue.
fp@369: 
fp@369: \subsubsection{Operation Mode}
fp@369: \index{Operation mode}
fp@369: 
fp@369: Operation mode is entered when a realtime module requests the master.
fp@369: The idle mode is stopped and the bus is scanned by getting the number
fp@369: of slaves and executing the ``Slave scan state machine'' (see
fp@369: section~\ref{sec:fsm-scan}) for each slave. The master is now ready to
fp@369: create domains and accept PDO registrations and slave configurations.
fp@369: After that, cyclic communication can be done by the realtime module.
fp@369: 
fp@369: \paragraph{Master Phases}
fp@369: 
fp@369: Every realtime module should use the master in three phases:
fp@369: 
fp@369: \begin{enumerate}
fp@369: \item \textit{Startup} - The master is requested and the bus is
fp@369:   validated. Domains are created and PDOs are registered. Slave
fp@369:   configurations are applied.
fp@369: \item \textit{Operation} - Cyclic code is run, process data is
fp@369:   exchanged and the master state machine is executed.
fp@369: \item \textit{Shutdown} - Cyclic code is stopped and the master
fp@369:   is released.
fp@369: \end{enumerate}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Device Modules}
fp@369: \label{sec:device}
fp@369: \index{Device modules}
fp@369: 
fp@369: Device modules are network device driver modules that handle Ethernet
fp@369: devices, which the master can use to connect to an EtherCAT bus.
fp@369: 
fp@369: Section~\ref{sec:networkdrivers} offers an overview of general Linux
fp@369: network driver modules, while section~\ref{sec:requirements} will show
fp@369: the requirements to an EtherCAT-enabled network driver. Finally,
fp@369: sections~\ref{sec:seldev} to~\ref{sec:patching} show how to fulfill
fp@369: these requirements and implement such a driver module.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Network Driver Basics}
fp@369: \label{sec:networkdrivers}
fp@369: \index{Network drivers}
fp@369: 
fp@369: EtherCAT relies on Ethernet hardware and the master needs a physical
fp@369: Ethernet device to communicate with the bus. Therefore it is necessary
fp@369: to understand how Linux handles network devices and their drivers,
fp@369: respectively.
fp@369: 
fp@369: \paragraph{Tasks of a Network Driver}
fp@369: 
fp@369: Network device drivers handle the lower two layers of the OSI model,
fp@369: that is the physical layer and the data-link layer. A network device
fp@369: itself natively handles the physical layer issues: It represents the
fp@369: hardware to connect to the medium and to send and receive data in the
fp@369: way, the physical layer protocol describes. The network device driver
fp@369: is responsible for getting data from the kernel's networking stack and
fp@369: forwarding it to the hardware, that does the physical transmission.
fp@369: If data is received by the hardware respectively, the driver is
fp@369: notified (usually by means of an interrupt) and has to read the data
fp@369: from the hardware memory and forward it to the network stack. There
fp@369: are a few more tasks, a network device driver has to handle, including
fp@369: queue control, statistics and device dependent features.
fp@369: 
fp@369: \paragraph{Driver Startup}
fp@369: 
fp@369: Usually, a driver searches for compatible devices on module loading.
fp@369: For PCI drivers, this is done by scanning the PCI bus and checking for
fp@369: known device IDs. If a device is found, data structures are allocated
fp@369: and the device is taken into operation.
fp@369: 
fp@369: \paragraph{Interrupt Operation}
fp@369: \index{Interrupt}
fp@369: 
fp@369: A network device usually provides a hardware interrupt that is used to
fp@369: notify the driver of received frames and success of transmittion, or
fp@369: errors, respectively. The driver has to register an interrupt service
fp@369: routine (ISR\index{ISR}\nomenclature{ISR}{Interrupt Service Routine}),
fp@369: that is executed each time, the hardware signals such an event. If the
fp@369: interrupt was thrown by the own device (multiple devices can share one
fp@369: hardware interrupt), the reason for the interrupt has to be determined
fp@369: by reading the device's interrupt register. For example, if the flag
fp@369: for received frames is set, frame data has to be copied from hardware
fp@369: to kernel memory and passed to the network stack.
fp@369: 
fp@369: \paragraph{The net\_device structure}
fp@369: \index{net\_device}
fp@369: 
fp@369: The driver registers a \textit{net\_device} structure for each device
fp@369: to communicate with the network stack and to create a ``network
fp@369: interface''. In case of an Ethernet driver, this interface appears as
fp@369: \textit{ethX}, where X is a number assigned by the kernel on
fp@369: registration. The \textit{net\_device} structure receives events
fp@369: (either from user space or from the network stack) via serveral
fp@369: callbacks, which have to be set before registration. Not every
fp@369: callback is mandatory, but for reasonable operation the ones below are
fp@369: needed in any case:
fp@369: 
fp@369: \begin{description}
fp@369: \item[int (*open)(struct net\_device *)] This function is called when
fp@369:   network communication has to be started, for example after a command
fp@369:   \textit{ifconfig ethX up} from user space. Frame reception has to be
fp@369:   enabled by the driver.
fp@369: \item[int (*stop)(struct net\_device *)] The purpose of this callback
fp@369:   is to ``close'' the device, i.~e. make the hardware stop receiving
fp@369:   frames.
fp@369: \item[int (*hard\_start\_xmit)(struct sk\_buff *, struct net\_device
fp@369:   *)] This function is cal\-led for each frame that has to be
fp@369:   transmitted.  The network stack passes the frame as a pointer to an
fp@369:   \textit{sk\_buff} structure (``socket buffer''\index{Socket buffer},
fp@369:   see below), which has to be freed after sending.
fp@369: \item[struct net\_device\_stats *(*get\_stats)(struct net\_device *)]
fp@369:   This call has to return a pointer to the device's
fp@369:   \textit{net\_device\_stats} structure, which permanently has to be
fp@369:   filled with frame statistics. This means, that everytime a frame is
fp@369:   received, sent, or an error happened, the appropriate counter in
fp@369:   this structure has to be increased.
fp@369: \end{description}
fp@369: 
fp@369: The actual registration is done with the \textit{register\_netdev()}
fp@369: call, unregistering is done with \textit{unregister\_netdev()}.
fp@369: 
fp@369: \paragraph{The netif Interface}
fp@369: \index{netif}
fp@369: 
fp@369: All other communication in the direction interface $\to$ network stack
fp@369: is done via the \textit{netif\_*} calls. For example, on successful
fp@369: device opening, the network stack has to be notified, that it can now
fp@369: pass frames to the interface. This is done by calling
fp@369: \textit{netif\_start\_queue()}. After this call, the
fp@369: \textit{hard\_start\_xmit()} callback can be called by the network
fp@369: stack. Furthermore a network driver usually manages a frame
fp@369: transmission queue. If this gets filled up, the network stack has to
fp@369: be told to stop passing further frames for a while. This happens with
fp@369: a call to \textit{netif\_stop\_queue()}. If some frames have been
fp@369: sent, and there is enough space again to queue new frames, this can be
fp@369: notified with \textit{netif\_wake\_queue()}. Another important call is
fp@369: \textit{netif\_receive\_skb()}\footnote{This function is part of the
fp@369:   NAPI (``New API''), that replaces the ``old'' kernel 2.4 technique
fp@369:   for interfacing to the network stack (with \textit{netif\_rx()}).
fp@369:   NAPI is a technique to improve network performance on Linux. Read
fp@369:   more in
fp@369:   http://www.cyberus.ca/\textasciitilde{}hadi/usenix-paper.tgz}: It
fp@369: passes a frame to the network stack, that was just received by the
fp@369: device.  Frame data has to be packed into a so-called ``socket
fp@369: buffer'' for that (see below).
fp@369: 
fp@369: \paragraph{Socket Buffers}
fp@369: \index{Socket buffer}
fp@369: 
fp@369: Socket buffers are the basic data type for the whole network stack.
fp@369: They serve as containers for network data and are able to quickly add
fp@369: data headers and footers, or strip them off again. Therefore a socket
fp@369: buffer consists of an allocated buffer and serveral pointers that mark
fp@369: beginning of the buffer (\textit{head}), beginning of data
fp@369: (\textit{data}), end of data (\textit{tail}) and end of buffer
fp@369: (\textit{end}). In addition, a socket buffer holds network header
fp@369: information and (in case of received data) a pointer to the
fp@369: \textit{net\_device}, it was received on. There exist functions that
fp@369: create a socket buffer (\textit{dev\_alloc\_skb()}), add data either
fp@369: from front (\textit{skb\_push()}) or back (\textit{skb\_put()}),
fp@369: remove data from front (\textit{skb\_pull()}) or back
fp@369: (\textit{skb\_trim()}), or delete the buffer (\textit{kfree\_skb()}).
fp@369: A socket buffer is passed from layer to layer, and is freed by the
fp@369: layer that uses it the last time. In case of sending, freeing has to
fp@369: be done by the network driver.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{EtherCAT Network Drivers}
fp@369: \label{sec:requirements}
fp@369: 
fp@369: There are a few requirements for Ethernet network devices to function
fp@369: as EtherCAT devices, when connected to an EtherCAT bus.
fp@369: 
fp@369: \paragraph{Dedicated Interfaces}
fp@369: 
fp@369: For performance and realtime purposes, the EtherCAT master needs
fp@369: direct and exclusive access to the Ethernet hardware. This implies
fp@369: that the network device must not be connected to the kernel's network
fp@369: stack as usual, because the kernel would try to use it as an ordinary
fp@369: Ethernet device.
fp@369: 
fp@369: \paragraph{Interrupt-less Operation}
fp@369: \index{Interrupt}
fp@369: 
fp@369: EtherCAT frames travel through the logical EtherCAT ring and are then
fp@369: sent back to the master. Communication is highly deterministic: A
fp@369: frame is sent and will be received again after a constant time.
fp@369: Therefore, there is no need to notify the driver about frame
fp@369: reception: The master can instead query the hardware for received
fp@369: frames.
fp@369: 
fp@369: Figure~\ref{fig:interrupt} shows two workflows for cyclic frame
fp@369: transmittion and reception with and without interrupts.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.8\textwidth]{images/interrupt}
fp@369:   \caption{Interrupt Operation versus Interrupt-less Operation}
fp@369:   \label{fig:interrupt}
fp@369: \end{figure}
fp@369: 
fp@369: In the left workflow ``Interrupt Operation'', the data from the last
fp@369: cycle is first processed and a new frame is assembled with new
fp@369: datagrams, which is then sent.  The cyclic work is done for now.
fp@369: Later, when the frame is received again by the hardware, an interrupt
fp@369: is triggered and the ISR is executed. The ISR will fetch the frame
fp@369: data from the hardware and initiate the frame dissection: The
fp@369: datagrams will be processed, so that the data is ready for processing
fp@369: in the next cycle.
fp@369: 
fp@369: In the right workflow ``Interrupt-less Operation'', there is no
fp@369: hardware interrupt enabled.  Instead, the hardware will be polled by
fp@369: the master by executing the ISR. If the frame has been received in the
fp@369: meantime, it will be dissected. The situation is now the same as at
fp@369: the beginning of the left workflow: The received data is processed and
fp@369: a new frame is assembled and sent. There is nothing to do for the rest
fp@369: of the cycle.
fp@369: 
fp@369: The interrupt-less operation is desirable, because there is simply no
fp@369: need for an interrupt. Moreover hardware interrupts are not conducive
fp@369: in improving the driver's realtime behaviour: Their undeterministic
fp@369: incidences contribute to increasing the jitter. Besides, if a realtime
fp@369: extension (like RTAI) is used, some additional effort would have to be
fp@369: made to priorize interrupts.
fp@369: 
fp@369: \paragraph{Ethernet and EtherCAT Devices}
fp@369: 
fp@369: Another issue lies in the way Linux handles devices of the same type.
fp@369: For example, a PCI\nomenclature{PCI}{Peripheral Component
fp@369:   Interconnect, Computer Bus} driver scans the PCI bus for devices it
fp@369: can handle. Then it registers itself as the responsible driver for all
fp@369: of the devices found. The problem is, that an unmodified driver can
fp@369: not be told to ignore a device because it will be used for EtherCAT
fp@369: later. There must be a way to handle multiple devices of the same
fp@369: type, where one is reserved for EtherCAT, while the other is treated
fp@369: as an ordinary Ethernet device.
fp@369: 
fp@369: For all this reasons, the author has decided that the only acceptable
fp@369: solution is to modify standard Ethernet drivers in a way that they
fp@369: keep their normal functionality, but gain the ability to treat one or
fp@369: more of the devices as EtherCAT-capable.
fp@369: 
fp@369: Below are the advantages of this solution:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item No need to tell the standard drivers to ignore certain devices.
fp@369: \item One networking driver for EtherCAT and non-EtherCAT devices.
fp@369: \item No need to implement a network driver from scratch and running
fp@369:   into issues, the former developers already solved.
fp@369: \end{itemize}
fp@369: 
fp@369: The chosen approach has the following disadvantages:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item The modified driver gets more complicated, as it must handle
fp@369:   EtherCAT and non-EtherCAT devices.
fp@369: \item Many additional case differentiations in the driver code.
fp@369: \item Changes and bugfixes on the standard drivers have to be ported
fp@369:   to the Ether\-CAT-capable versions from time to time.
fp@369: \end{itemize}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Device Selection}
fp@369: \label{sec:seldev}
fp@369: 
fp@369: After loading the master module, at least one EtherCAT-capable network
fp@369: driver module has to be loaded, that connects one of its devices to
fp@369: the master. To specify an EtherCAT device and the master to connect
fp@369: to, all EtherCAT-capable network driver modules should provide two
fp@369: module parameters:
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_device\_index] PCI device index of the device that is
fp@369:   connected to the EtherCAT bus. If this parameter is left away, all
fp@369:   devices found are treated as ordinary Ethernet devices. Default:
fp@369:   $-1$
fp@369: \item[ec\_master\_index] Index of the master to connect to. Default:
fp@369:   $0$
fp@369: \end{description}
fp@369: 
fp@369: The following command loads the EtherCAT-capable RTL8139 device
fp@369: driver, telling it to handle the second device as an EtherCAT device
fp@369: and connecting it to the first master:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{modprobe ec\_8139too ec\_device\_index=1}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: Usually, this command does not have to be entered manually, but is
fp@369: called by the EtherCAT init script. See section~\ref{sec:init} for
fp@369: more information.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Device Interface}
fp@369: \label{sec:ecdev}
fp@369: \index{Device interface}
fp@369: 
fp@369: An anticipation to the section about the master module
fp@369: (section~\ref{sec:mastermod}) has to be made in order to understand
fp@369: the way, a network device driver module can connect a device to a
fp@369: specific EtherCAT master.
fp@369: 
fp@369: The master module provides a ``device interface'' for network device
fp@369: drivers. To use this interface, a network device driver module must
fp@369: include the header
fp@369: \textit{devices/ecdev.h}\nomenclature{ecdev}{EtherCAT Device}, coming
fp@369: with the EtherCAT master code. This header offers a function interface
fp@369: for EtherCAT devices which is explained below. All functions of the
fp@369: device interface are named with the prefix \textit{ecdev}.
fp@369: 
fp@369: \paragraph{Device Registration}
fp@369: 
fp@369: A network device driver can connect a physical device to an EtherCAT
fp@369: master with the \textit{ecdev\_register()} function.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   ec_device_t *ecdev_register(unsigned int master_index,
fp@369:                               struct net_device *net_dev,
fp@369:                               ec_isr_t isr,
fp@369:                               struct module *module);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The first parameter \textit{master\_index} must be the index of the
fp@369: EtherCAT master to connect to (see section~\ref{sec:mastermod}),
fp@369: followed by \textit{net\_dev}, the pointer to the corresponding
fp@369: net\_device structure, which represents the network device to connect.
fp@369: The third parameter \textit{isr} must be a pointer to the interrupt
fp@369: service routine (ISR\index{ISR}) handling the device. The master will
fp@369: later execute the ISR in order to receive frames and to update the
fp@369: device status. The last parameter \textit{module} must be the pointer
fp@369: to the device driver module, which is usually accessible via the macro
fp@369: \textit{THIS\_MODULE} (see next paragraph). On success, the function
fp@369: returns a pointer to an \textit{ec\_device\_t} object, which has to be
fp@369: specified when calling further functions of the device interface.
fp@369: Therefore the device module has to store this pointer for future use.
fp@369: In error case, the \textit{ecdev\_register()} returns \textit{NULL},
fp@369: which means that the device could not be registered.  The reason for
fp@369: this is printed to \textit{syslog}\index{syslog}. In this case, the
fp@369: device module is supposed to abort the module initialisation and let
fp@369: the \textit{insmod} command fail.
fp@369: 
fp@369: \paragraph{Implicit Dependencies}
fp@369: 
fp@369: The reason for the module pointer has to be specified at device
fp@369: registration is a non-trivial one: The master has to know about the
fp@369: module, because there will be an implicit dependency between the
fp@369: device module and a later connected realtime module: When a realtime
fp@369: module connects to the master, the use count of the master module will
fp@369: be increased, so that the master module can not be unloaded for the
fp@369: time of the connection. This is reasonable, and so automatically done
fp@369: by the kernel. The kernel knows about this dependency, because the
fp@369: realtime module uses kernel symbols provided by the master module.
fp@369: Moreover it is mandatory, that the device module can be unloaded
fp@369: neither, because it is implicitely used by the realtime module, too.
fp@369: Unloading it would lead to a fatal situation, because the master would
fp@369: have no device to send and receive frames for the realtime module.
fp@369: This dependency can not be detected automatically, because the
fp@369: realtime module does not use any symbols of the device module.
fp@369: Therefore the master explicitly increments the use counter of the
fp@369: connected device module upon connection of a realtime module and
fp@369: decrements it, if the realtime module disconnects. In this manner, it
fp@369: is impossible to unload a device module while the master is in use.
fp@369: This is done with the kernel function pair \textit{try\_module\_get()}
fp@369: \index{try\_module\_get@\textit{try\_module\_get()}} and
fp@369: \textit{module\_put()} \index{module\_put@\textit{module\_put()}}. The
fp@369: first one increases the use count of a module and only fails, if the
fp@369: module is currenly being unloaded. The last one decreases the use
fp@369: count again and never fails. Both functions take a pointer to the
fp@369: module as their argument, which the device module therefore has to
fp@369: specify upon device registration.
fp@369: 
fp@369: \paragraph{Device Unregistering}
fp@369: 
fp@369: The unregistration of a device is usually done in the device module's
fp@369: cleanup function, by calling the \textit{ecdev\_unregister()} function
fp@369: and specifying the master index and a pointer to the device object
fp@369: again.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecdev_unregister(unsigned int master_index,
fp@369:                         ec_device_t *device);
fp@369: \end{lstlisting}
fp@369: 
fp@369: This function can fail too (if the master index is invalid, or the
fp@369: given device was not registered), but due to the fact, that this
fp@369: failure can not be dealt with appropriately, because the device module
fp@369: is unloading anyway, the failure code would not be of any interest. So
fp@369: the function has a void return value.
fp@369: 
fp@369: \paragraph{Starting the Master}
fp@369: 
fp@369: When a device has been initialized completely and is ready to send and
fp@369: receive frames, the master has to be notified about this by calling
fp@369: the \textit{ecdev\_start()} function.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecdev_start(unsigned int master_index);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The master will then enter ``Idle Mode'' and start scanning the bus
fp@369: (and possibly handling EoE slaves). Moreover it will make the bus
fp@369: accessible via Sysfs interface and react to user interactions. The
fp@369: function takes one parameter \textit{master\_index}, which has to be
fp@369: the same as at the call to \textit{ecdev\_register()}. The return
fp@369: value will be non-zero if the starting process failed. In this case
fp@369: the device module is supposed to abort the init sequence and make the
fp@369: init function return an error code.
fp@369: 
fp@369: \paragraph{Stopping the Master}
fp@369: 
fp@369: Before a device can be unregistered, the master has to be stopped by
fp@369: calling the \textit{ecdev\_stop()} function. It will stop processing
fp@369: messages of EoE slaves and leave ``Idle Mode''. The only parameter is
fp@369: \textit{master\_index}. This function can not fail.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecdev_stop(unsigned int master_index);
fp@369: \end{lstlisting}
fp@369: 
fp@369: A subsequent call to \textit{ecdev\_unregister()} will now unregister
fp@369: the device savely.
fp@369: 
fp@369: \paragraph{Receiving Frames}
fp@369: 
fp@369: The interrupt service routine handling device events usually has a
fp@369: section where new frames are fetched from the hardware and forwarded
fp@369: to the kernel network stack via \textit{netif\_receive\_skb()}. For an
fp@369: EtherCAT-capable device, this has to be replaced by calling the
fp@369: \textit{ecdev\_receive()} function to forward the received data to the
fp@369: connected EtherCAT master instead.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecdev_receive(ec_device_t *device,
fp@369:                      const void *data,
fp@369:                      size_t size);
fp@369: \end{lstlisting}
fp@369: 
fp@369: This function takes 3 arguments, a pointer to the device object
fp@369: (\textit{device}), a pointer to the received data, and the size of the
fp@369: received data. The data range has to include the Ethernet headers
fp@369: starting with the destination address and reach up to the last octet
fp@369: of EtherCAT data, excluding the FCS. Most network devices handle the
fp@369: FCS in hardware, so it is not seen by the driver code and therefore
fp@369: doesn't have to be cut off manually.
fp@369: 
fp@369: \paragraph{Handling the Link Status}
fp@369: 
fp@369: Information about the link status (i.~e. if there is a carrier signal
fp@369: detected on the physical port) is also important to the master. This
fp@369: information is usually gathered by the ISR and should be forwarded to
fp@369: the master by calling the \textit{ecdev\_link\_state()} function. The
fp@369: master then can react on this and warn the realtime module of a lost
fp@369: link.
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecdev_link_state(ec_device_t *device,
fp@369:                         uint8_t new_state);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The parameter \textit{device} has to be a pointer to the device object
fp@369: returned by \textit{ecdev\_\-register()}. With the second parameter
fp@369: \textit{new\_state}, the new link state is passed: 1, if the link went
fp@369: up, and 0, if it went down.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Patching Network Drivers}
fp@369: \label{sec:patching}
fp@369: \index{Network drivers}
fp@369: 
fp@369: This section will demonstrate, how to make a standard Ethernet driver
fp@369: EtherCAT-capable. The below code examples are taken out of the
fp@369: modified RealTek RTL8139 driver coming with the EtherCAT master
fp@369: (\textit{devices/8139too.c}). The driver was originally developed by
fp@369: Donald Becker, and is currently maintained by Jeff Garzik.
fp@369: 
fp@369: Unfortunately, there is no standard procedure to enable an Ethernet
fp@369: driver for use with the EtherCAT master, but there are a few common
fp@369: techniques, that are described in this section.
fp@369: 
fp@369: \begin{enumerate}
fp@369: \item A first simple rule is, that \textit{netif\_*()}-calls must be
fp@369:   strictly avoided for all EtherCAT devices. As mentioned before,
fp@369:   EtherCAT devices have no connection to the network stack, and
fp@369:   therefore must not call its interface functions.
fp@369: \item Another important thing is, that EtherCAT devices should be
fp@369:   operated without interrupts. So any calls of registering interrupt
fp@369:   handlers and enabling interrupts at hardware level must be avoided,
fp@369:   too.
fp@369: \item The master does not use a new socket buffer for each send
fp@369:   operation: Instead there is a fix one allocated on master
fp@369:   initialization. This socket buffer is filled with an EtherCAT frame
fp@369:   with every send operation and passed to the
fp@369:   \textit{hard\_start\_xmit()} callback. For that it is necessary,
fp@369:   that the socket buffer is not be freed by the network driver as
fp@369:   usual.
fp@369: \end{enumerate}
fp@369: 
fp@369: As mentioned before, the driver will handle both EtherCAT and ordinary
fp@369: Ethernet devices. This implies, that for each device-dependent
fp@369: operation, it has to be checked if an EtherCAT device is involved, or
fp@369: just an Ethernet device. For means of simplicity, this example driver
fp@369: will only handle one EtherCAT device. This makes the case
fp@369: differentiations easier.
fp@369: 
fp@369: \paragraph{Global Variables}
fp@369: 
fp@369: First of all, there have to be additional global variables declared,
fp@369: as shown in the listing:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   static int ec_device_index = -1;
fp@369:   static int ec_device_master_index = 0;
fp@369:   static ec_device_t *rtl_ec_dev;
fp@369:   struct net_device *rtl_ec_net_dev = NULL;
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1} -- \textcircled{\tiny 2}] To
fp@369:   comply to the requirements for parameters of EtherCAT device modules
fp@369:   described in section~\ref{sec:seldev}, there have to be additional
fp@369:   parameter variables: \textit{ec\_\-device\_\-index} holds the index
fp@369:   of the EtherCAT device and defaults to $-1$ (no EtherCAT device),
fp@369:   while \textit{ec\_device\_master\_index} stores index of the master,
fp@369:   the single device will be connected to. Default: $0$
fp@369: \item[\normalfont\textcircled{\tiny 3}] \textit{rtl\_ec\_dev} will be
fp@369:   the pointer to the later registered RealTek EtherCAT device, which
fp@369:   can be used as a parameter for device methods.
fp@369: \item[\normalfont\textcircled{\tiny 4}] \textit{rtl\_ec\_net\_dev} is
fp@369:   a pointer to the \textit{net\_device} structure of the dedicated
fp@369:   device and is set while scanning the PCI bus and finding the device
fp@369:   with the specified index. This is done inside the
fp@369:   \textit{pci\_module\_init()} function executed as the first thing on
fp@369:   module loading.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Module Initialization}
fp@369: 
fp@369: Below is the (shortened) coding of the device driver's module init
fp@369: function:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   static int __init rtl8139_init_module(void)
fp@369:   {
fp@369:           if (pci_module_init(&rtl8139_pci_driver) < 0) {
fp@369:                   printk(KERN_ERR "Failed to init PCI mod.\n");
fp@369:                   goto out_return;
fp@369:           }
fp@369: 
fp@369:           if (rtl_ec_net_dev) {
fp@369:                   printk(KERN_INFO "Registering"
fp@369:                          " EtherCAT device...\n");
fp@369:                   if (!(rtl_ec_dev =
fp@369:                           ecdev_register(ec_device_master_index,
fp@369:                                          rtl_ec_net_dev,
fp@369:                                          rtl8139_interrupt,
fp@369:                                          THIS_MODULE))) {
fp@369:                           printk(KERN_ERR "Failed to reg."
fp@369:                                           " EtherCAT device!\n");
fp@369:                           goto out_unreg_pci;
fp@369:                   }
fp@369: 
fp@369:                   printk(KERN_INFO "Starting EtherCAT"
fp@369:                          " device...\n");
fp@369:                   if (ecdev_start(ec_device_master_index)) {
fp@369:                           printk(KERN_ERR "Failed to start"
fp@369:                                  " EtherCAT device!\n");
fp@369:                           goto out_unreg_ec;
fp@369:                   }
fp@369:           } else {
fp@369:                   printk(KERN_WARNING "No EtherCAT device"
fp@369:                          " registered!\n");
fp@369:           }
fp@369: 
fp@369:           return 0;
fp@369: 
fp@369:       out_unreg_ec:
fp@369:           ecdev_unregister(ec_device_master_index, rtl_ec_dev);
fp@369:       out_unreg_pci:
fp@369:           pci_unregister_driver(&rtl8139_pci_driver);
fp@369:       out_return:
fp@369:           return -1;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] This call initializes all
fp@369:   RTL8139-compatible devices found on the pci bus. If a device with
fp@369:   index \textit{ec\_device\_index} is found, a pointer to its
fp@369:   \textit{net\_device} structure is stored in
fp@369:   \textit{rtl\_ec\_net\_dev} for later use (see next listings).
fp@369: \item[\normalfont\textcircled{\tiny 8}] If the specified device was
fp@369:   found, \textit{rtl\_ec\_net\_dev} is non-zero.
fp@369: \item[\normalfont\textcircled{\tiny 11}] The device is connected to
fp@369:   the specified master with a call to \textit{ecdev\_register()}. If
fp@369:   this fails, module loading is aborted.
fp@369: \item[\normalfont\textcircled{\tiny 23}] The device registration was
fp@369:   successful and the master is started. This can fail, which aborts
fp@369:   module loading.
fp@369: \item[\normalfont\textcircled{\tiny 29}] If no EtherCAT device was
fp@369:   found, a warning is output.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Device Searching}
fp@369: 
fp@369: During the PCI initialization phase, a variable \textit{board\_idx} is
fp@369: increased for each RTL8139-compatible device found. The code below is
fp@369: executed for each device:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (board_idx == ec_device_index) {
fp@369:           rtl_ec_net_dev = dev;
fp@369:           strcpy(dev->name, "ec0");
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1}] The device with the specified
fp@369:   index will be the EtherCAT device.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Avoiding Device Registration}
fp@369: 
fp@369: Later in the PCI initialization phase, the net\_devices get
fp@369: registered. This has to be avoided for EtherCAT devices and so this is
fp@369: a typical example for an EtherCAT case differentiation:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (dev != rtl_ec_net_dev) {
fp@369:           i = register_netdev(dev);
fp@369:           if (i) goto err_out;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1}] If the current net\_device is
fp@369:   not the EtherCAT device, it is registered at the network stack.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Avoiding Interrupt Registration}
fp@369: 
fp@369: In the next two listings, there is an interrupt requested and the
fp@369: device's interrupts are enabled. This also has to be encapsulated by
fp@369: if-clauses, because interrupt operation is not wanted for EtherCAT
fp@369: devices.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (dev != rtl_ec_net_dev) {
fp@369:           retval = request_irq(dev->irq, rtl8139_interrupt,
fp@369:                                SA_SHIRQ, dev->name, dev);
fp@369:           if (retval) return retval;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (dev != rtl_ec_net_dev) {
fp@369:           /* Enable all known interrupts by setting
fp@369:              the interrupt mask. */
fp@369:           RTL_W16(IntrMask, rtl8139_intr_mask);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \paragraph{Frame Sending}
fp@369: 
fp@369: The listing below shows an exerpt of the function representing the
fp@369: \textit{hard\_start\_xmit()} callback of the net\_device.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   /* Note: the chip doesn't have auto-pad! */
fp@369:   if (likely(len < TX_BUF_SIZE)) {
fp@369:           if (len < ETH_ZLEN)
fp@369:                   memset(tp->tx_buf[entry], 0, ETH_ZLEN);
fp@369:           skb_copy_and_csum_dev(skb, tp->tx_buf[entry]);
fp@369:           if (dev != rtl_ec_net_dev) {
fp@369:                   dev_kfree_skb(skb);
fp@369:           }
fp@369:   } else {
fp@369:           if (dev != rtl_ec_net_dev) {
fp@369:                   dev_kfree_skb(skb);
fp@369:           }
fp@369:           tp->stats.tx_dropped++;
fp@369:           return 0;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 6} + \textcircled{\tiny 10}] The
fp@369:   master uses a fixed socket buffer for transmission, which is reused
fp@369:   and may not be freed.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Frame Receiving}
fp@369: 
fp@369: During ordinary frame reception, a socket buffer is created and filled
fp@369: with the received data. This is not necessary for an EtherCAT device:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (dev != rtl_ec_net_dev) {
fp@369:           /* Malloc up new buffer, compatible with net-2e. */
fp@369:           /* Omit the four octet CRC from the length. */
fp@369: 
fp@369:           skb = dev_alloc_skb (pkt_size + 2);
fp@369:           if (likely(skb)) {
fp@369:                   skb->dev = dev;
fp@369:                   skb_reserve(skb, 2); /* 16 byte align
fp@369:                                           the IP fields. */
fp@369:                   eth_copy_and_sum(skb, &rx_ring[ring_off + 4],
fp@369:                                    pkt_size, 0);
fp@369:                   skb_put(skb, pkt_size);
fp@369:                   skb->protocol = eth_type_trans(skb, dev);
fp@369: 
fp@369:                   dev->last_rx = jiffies;
fp@369:                   tp->stats.rx_bytes += pkt_size;
fp@369:                   tp->stats.rx_packets++;
fp@369: 
fp@369:                   netif_receive_skb (skb);
fp@369:           } else {
fp@369:                   if (net_ratelimit())
fp@369:                           printk(KERN_WARNING
fp@369:                                  "%s: Memory squeeze, dropping"
fp@369:                                  " packet.\n", dev->name);
fp@369:                   tp->stats.rx_dropped++;
fp@369:           }
fp@369:   } else {
fp@369:           ecdev_receive(rtl_ec_dev,
fp@369:                         &rx_ring[ring_offset + 4], pkt_size);
fp@369:           dev->last_rx = jiffies;
fp@369:           tp->stats.rx_bytes += pkt_size;
fp@369:           tp->stats.rx_packets++;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 28}] If the device is an EtherCAT
fp@369:   device, no socket buffer is allocated. Instead a pointer to the data
fp@369:   (which is still in the device's receive ring) is passed to the
fp@369:   EtherCAT master. Unnecessary copy operations are avoided.
fp@369: \item[\normalfont\textcircled{\tiny 30} -- \textcircled{\tiny 32}] The
fp@369:   device's statistics are updated as usual.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Link State}
fp@369: 
fp@369: The link state (i.~e. if there is a carrier signal detected on the
fp@369: receive port) is determined during execution of the ISR. The listing
fp@369: below shows the different processing for Ethernet and EtherCAT
fp@369: devices:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   if (dev != rtl_ec_net_dev) {
fp@369:           if (tp->phys[0] >= 0) {
fp@369:                   mii_check_media(&tp->mii, netif_msg_link(tp),
fp@369:                                   init_media);
fp@369:           }
fp@369:   } else {
fp@369:           void __iomem *ioaddr = tp->mmio_addr;
fp@369:           uint16_t link = RTL_R16(BasicModeStatus)
fp@369:                           & BMSR_LSTATUS;
fp@369:           ecdev_link_state(rtl_ec_dev, link ? 1 : 0);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] The ``media check'' is done
fp@369:   via the media independent interface (MII\nomenclature{MII}{Media
fp@369:     Independent Interface}), a standard interface for Fast Ethernet
fp@369:   devices.
fp@369: \item[\normalfont\textcircled{\tiny 7} -- \textcircled{\tiny 10}] For
fp@369:   EtherCAT devices, the link state is fetched manually from the
fp@369:   appropriate device register, and passed to the EtherCAT master by
fp@369:   calling \textit{ecdev\_\-link\_\-state()}.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Module Cleanup}
fp@369: 
fp@369: Below is the module's cleanup function:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   static void __exit rtl8139_cleanup_module (void)
fp@369:   {
fp@369:           printk(KERN_INFO "Cleaning up RTL8139-EtherCAT"
fp@369:                  " module...\n");
fp@369: 
fp@369:           if (rtl_ec_net_dev) {
fp@369:                   printk(KERN_INFO "Stopping device...\n");
fp@369:                   ecdev_stop(ec_device_master_index);
fp@369:                   printk(KERN_INFO "Unregistering device...\n");
fp@369:                   ecdev_unregister(ec_device_master_index,
fp@369:                                    rtl_ec_dev);
fp@369:                   rtl_ec_dev = NULL;
fp@369:           }
fp@369: 
fp@369:           pci_unregister_driver(&rtl8139_pci_driver);
fp@369: 
fp@369:           printk(KERN_INFO "RTL8139-EtherCAT module"
fp@369:                  " cleaned up.\n");
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 6}] Stopping and unregistration is
fp@369:   only done, if a device was registered before.
fp@369: \item[\normalfont\textcircled{\tiny 8}] The master is first stopped,
fp@369:   so it does not access the device any more.
fp@369: \item[\normalfont\textcircled{\tiny 10}] After this, the device is
fp@369:   unregistered. The master is now ``ophaned''.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{The Master Module}
fp@369: \label{sec:mastermod}
fp@369: \index{Master module}
fp@369: 
fp@369: The EtherCAT master is designed to run as a kernel module. Moreover
fp@369: the master kernel module \textit{ec\_master} can handle multiple
fp@369: masters at the same time: The number of masters has to be passed to
fp@369: the module with the parameter \textit{ec\_master\_count}, that
fp@369: defaults to $1$. A certain master can later be addressed by its index.
fp@369: For example, if the master module has been loaded with the command
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{modprobe ec\_master ec\_master\_count=2}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: the two masters can be addressed by their indices 0 and 1 respectively
fp@369: (see figure~\ref{fig:masters}). This master index mandatory for
fp@369: certain functions of the master interfaces.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.5\textwidth]{images/masters}
fp@369:   \caption{Multiple masters in one module}
fp@369:   \label{fig:masters}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Master Log Messages}
fp@369: 
fp@369: The master module gives information about it's state and events via
fp@369: the syslog interface. The module loading command above should result
fp@369: in the following syslog messages:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   EtherCAT: Master driver, 1.1 (stable) - rev. 513,
fp@369:             compiled by fp at Aug  09 2006 09:43:50
fp@369:   EtherCAT: Initializing 2 EtherCAT master(s)...
fp@369:   EtherCAT: Initializing master 0.
fp@369:   EtherCAT: Initializing master 1.
fp@369:   EtherCAT: Master driver initialized.
fp@369: \end{lstlisting}
fp@369: 
fp@369: The master provides information about it's version number, subversion
fp@369: revision number and compile information, like the date of compilation
fp@369: and the user, who compiled. All messages are prefixed either with
fp@369: \texttt{EtherCAT:}, \texttt{EtherCAT WARNING:} or \texttt{EtherCAT
fp@369:   ERROR:}, which makes searching the logs easier.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Class Reference}
fp@369: \label{sec:classes}
fp@369: 
fp@369: This section is not intended to be a complete reference of master
fp@369: classes and functions\footnote{The comprehensive master reference can
fp@369:   be obtained at http://etherlab.org/download/download-en.html}, but
fp@369: will give a general survey of the master's classes, and how they
fp@369: interact.
fp@369: 
fp@369: Figure~\ref{fig:uml-all} shows an UML class diagram of the master
fp@369: classes.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=\textwidth]{images/uml-all}
fp@369:   \caption{UML class diagram with associations}
fp@369:   \label{fig:uml-all}
fp@369: \end{figure}
fp@369: 
fp@369: The following subsections introduce serveral classes with their
fp@369: attributes and methods.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Master Class}
fp@369: \label{sec:class-master}
fp@369: \index{Master!Class}
fp@369: 
fp@369: Figure~\ref{fig:uml-master} shows an UML class diagram of the master
fp@369: class. There is a short explanation of the attributes and methods
fp@369: below.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.8\textwidth]{images/uml-master}
fp@369:   \caption{Master UML class diagram}
fp@369:   \label{fig:uml-master}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Master Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[list] is a listhead structure that is needed to manage the list
fp@369:   of masters in the master module (see section~\ref{sec:mastermod}).
fp@369: \item[reserved] is a flag, that marks the master as reserved for a
fp@369:   realtime module, so that a call to \textit{ecrt\_request\_master()}
fp@369:   fails, if another module is already using the master.
fp@369: \item[index] contains the number of the master. The first master will
fp@369:   get index 0, the second index 1, and so on.
fp@369: \item[kobj] In order to make the master object available via Sysfs
fp@369:   (see section~\ref{sec:sysfs}), this structure is needed inside the
fp@369:   master object (see section~\ref{sec:sysfs}).
fp@369: \item[slaves] is the list of slaves. It consists of objects of the
fp@369:   \textit{ec\_slave\_t} class (see section~\ref{sec:class-slave}).
fp@369: \item[slave\_count] is the number of slaves in the list.
fp@369: \item[device] points to the network device that is used by the master
fp@369:   to send and receive frames (see section~\ref{sec:class-device}). It
fp@369:   is \textit{NULL}, if no device is connected.
fp@369: \item[datagram\_queue] is a list of datagrams (see
fp@369:   section~\ref{sec:class-datagram}) that have to be sent by the
fp@369:   master, or have already been sent and wait to be received again.
fp@369:   Upon reception or error, the datagrams are dequeued.
fp@369: \item[datagram\_index] contains the index value for the next datagram.
fp@369:   The master stores this incrementing index into every datagram, to
fp@369:   make it easier to assign a received datagram to the one sent before.
fp@369: \item[domains] contains the list of domains created by the realtime
fp@369:   module (section~\ref{sec:class-domain}).
fp@369: \item[debug\_level] controls, how much debugging output is printed by
fp@369:   the master: 0 means no debugging output, 1 means to output certain
fp@369:   executing marks and actions, and 2 means to output frame contents in
fp@369:   addition. This value can be changed at runtime via the Sysfs
fp@369:   interface (see section~\ref{sec:sysfs}).
fp@369: \item[stats] is a statistics object that contains certain counters
fp@369:   (like the number of missed frames).  These statistics are output on
fp@369:   demand, but at most once a second.
fp@369: \item[workqueue] is the kernel workqueue used for idle mode.
fp@369: \item[idle\_work] is the work object, that is queued.
fp@369: \item[fsm] The attribute \textit{fsm} represents the master's finite
fp@369:   state machine, that does all the slave processing. See
fp@369:   sections~\ref{sec:class-fsm} and~\ref{sec:fsm} for further details.
fp@369: \item[mode] contains the current master mode, if it is orphaned, idle,
fp@369:   or in operation mode.
fp@369: \item[eoe\_timer] is the kernel timer used for EoE\index{EoE}
fp@369:   processing.
fp@369: \item[eoe\_running] marks the state of EoE processing.
fp@369: \item[eoe\_handlers] is the list of EoE handlers (see
fp@369:   section~\ref{sec:class-eoe}).
fp@369: \item[internal\_lock] is a spinlock used in idle mode, that controls
fp@369:   the concurrency of the idle and EoE processes.
fp@369: \item[request\_cb] The ``request lock'' callback function, the master
fp@369:   has to provide for foreign instances, which want to access the
fp@369:   master (see section~\ref{sec:concurr}).
fp@369: \item[release\_cb] The callback function that will release the master
fp@369:   lock.
fp@369: \item[cb\_data] This value will be passed as an argument to each
fp@369:   callback.
fp@369: \item[eeprom\_write\_enable] flag can be written via Sysfs to enable
fp@369:   the general writing of E$^2$PROM contents.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Master Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_master\_init()] is the master's constructor. It initializes
fp@369:   all attributes, creates the workqueue, creates EoE handlers and the
fp@369:   state machine object, and adds the kernel object to the Sysfs
fp@369:   hierarchy.
fp@369: \item[ec\_master\_clear()] is the destructor and undoes all these
fp@369:   actions.
fp@369: \item[ec\_master\_reset()] clears the master, but initializes it
fp@369:   again. This is needed, when a realtime module disconnects: Slaves
fp@369:   and other attributes are cleared and are later rebuilt by the idle
fp@369:   process.
fp@369: \item[ec\_master\_idle\_start/stop()] These methods enable or disable
fp@369:   the idle process.
fp@369: \item[ec\_master\_eoe\_start/stop()] These methods do the same for the
fp@369:   EoE timer.
fp@369: \item[ec\_master\_receive\_datagrams()] This method is called by the
fp@369:   device, which uses it to pass received frames to the master.  The
fp@369:   frame is dissected and the contained datagrams are assigned to the
fp@369:   datagram objects in the datagram queue, which are dequeued on
fp@369:   reception or error.
fp@369: \item[ec\_master\_queue\_datagram()] This method is used to queue a
fp@369:   new datagram for sending and receiving.
fp@369: \item[ec\_master\_output\_stats()] This method is cyclically called to
fp@369:   output a summary of the \textit{stats} attribute at most once a
fp@369:   second.
fp@369: \item[ec\_master\_clear\_slaves()] clears the list of slaves. This is
fp@369:   needed on connection/disconnection of a realtime module or at a
fp@369:   topology change in idle mode, when all slaves objects are rebuilt.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Private Master Methods}
fp@369: 
fp@369: A few of a master's methods are private, meaning, that they can only
fp@369: be called from other master methods:
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_master\_send\_datagrams()] searches the datagram queue for
fp@369:   unsent datagrams, allocates frames to send them, does the actual
fp@369:   sending and marks the datagrams as sent.
fp@369: \item[ec\_master\_idle\_run()] is the work function for the idle mode.
fp@369:   It executes the idle state machine, described in
fp@369:   section~\ref{sec:fsm-idle}.
fp@369: \item[ec\_master\_eoe\_run()] is called by the EoE timer and is
fp@369:   responsible for communicating with EoE-capable slaves. See
fp@369:   section~\ref{sec:eoeimp} for more information.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Master Methods (Realtime Interface)}
fp@369: 
fp@369: The master methods belonging to the Eth\-er\-CAT realtime
fp@369: interface\index{ecrt@\textit{ecrt}}\nomenclature{ecrt}{EtherCAT
fp@369:   Realtime Interface} begin with the prefix \textit{ecrt} instead of
fp@369: \textit{ec}. The functions of the realtime interface are explained in
fp@369: section~\ref{sec:ecrt-master}.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Slave Class}
fp@369: \label{sec:class-slave}
fp@369: \index{Slave!Class}
fp@369: 
fp@369: Figure~\ref{fig:uml-slave} shows an UML class diagram of the slave
fp@369: class. There is a short explanation of the attributes and methods
fp@369: below.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.8\textwidth]{images/uml-slave}
fp@369:   \caption{Slave UML class diagram}
fp@369:   \label{fig:uml-slave}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Slave Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[list] The master holds a slave list, therefore the slave class
fp@369:   must contain this structure used as an anchor for the linked
fp@369:   list.
fp@369: \item[kobj] This pointer serves as base object for the slave's Sysfs
fp@369:   representation.
fp@369: \item[master] is the pointer to the master owning this slave object.
fp@369: \item[ring\_position] is the logical position in the logical ring
fp@369:   topology.
fp@369: \item[station\_address] is the configured station address. This is
fp@369:   always the ring position~+~$1$).
fp@369: \item[coupler\_index] is the index of the last bus coupler.
fp@369: \item[coupler\_subindex] is the slave's position, counted from the
fp@369:   last bus coupler. See section~\ref{sec:addr} for more information.
fp@369: \item[base\_*] These attributes contain base information about the
fp@369:   slave, that are read from the ``DL Information'' attribute.
fp@369: \item[dl\_*] These fields store information of the ``DL Status''
fp@369:   attribute, for example states of the the communication ports.
fp@369: \item[sii\_*] These attributes contain values from the ``Slave
fp@369:   Information Interface'' \cite[section~6.4]{dlspec}, mostly identity
fp@369:   and mailbox information, but also the list of sync manager
fp@369:   configurations and PDOs.
fp@369: \item[registered] This flag is set, if one or more PDOs of the slave
fp@369:   have been registered for process data exchange. Otherwise a warning
fp@369:   is output, because the slave is unused.
fp@369: \item[fmmus] Is an array of FMMU configurations, that have to be
fp@369:   applied to the slave.
fp@369: \item[fmmu\_count] contains number of FMMUs used.
fp@369: \item[eeprom\_*] These fields contain E$^2$PROM contents and the
fp@369:   extracted category information \cite[section~5.4]{alspec}.
fp@369: \item[new\_eeprom\_data] If this pointer is not \textit{NULL}, it
fp@369:   points to new E$^2$PROM contents, that have to be written to the
fp@369:   slave.
fp@369: \item[new\_eeprom\_size] This field represents the size of the new
fp@369:   E$^2$PROM data.
fp@369: \item[requested\_state] is the requested slave state.
fp@369: \item[current\_state] is the current slave state.
fp@369: \item[error\_flag] is used by the operation and idle state machines
fp@369:   to indicate, that a state transisition has failed and should not be
fp@369:   tried again until an external event happens.
fp@369: \item[online] This flag contains the online state of the slave (i.~e.
fp@369:   if it currently responds to the masters commands). Changes of the
fp@369:   online state are always reported.
fp@369: \item[varsize\_fields] is only suitable for slaves that provide PDOs
fp@369:   of variable size (like slaves that manage a sub-fieldbus) and
fp@369:   contains information about what size this fields actually should
fp@369:   have.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Slave Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_slave\_init()] The slave's constructor.
fp@369: \item[ec\_slave\_clear()] The slave's destructor.
fp@369: \item[ec\_prepare\_fmmu()] prepares an FMMU configuration. The FMMU is
fp@369:   configured for a certain sync manager and domain.
fp@369: \item[ec\_fetch\_*()] Serveral methods to extract information of the
fp@369:   E$^2$PROM category contents.
fp@369: \item[ec\_slave\_locate\_string()] extracts a string out of a STRING
fp@369:   category and allocates string memory.
fp@369: \item[ec\_slave\_calc\_sync\_size()] calculates the size of sync
fp@369:   manager contents, because they can be variable due to variable-sized
fp@369:   PDOs.
fp@369: \item[ec\_slave\_info()] This method prints all slave information into
fp@369:   a buffer for Sysfs reading.
fp@369: \item[ec\_slave\_mbox\_*()] These functions prepare datagrams for
fp@369:   mailbox communication, or process mailbox responses, respectively.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Private Slave Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_slave\_write\_eeprom()] This function accepts E$^2$PROM data
fp@369:   from user space, does a quick validation of the contents and
fp@369:   schedules them for writing through the idle state machine.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Slave Methods (Realtime Interface)}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ecrt\_slave\_conf\_sdo*()] These methods accept SDO
fp@369:   configurations, that are applied on slave activation (i.~e.
fp@369:   everytime the slave is configured). The methods differ only in the
fp@369:   data size of the SDO (8, 16 or 32 bit).
fp@369: \item[ecrt\_slave\_pdo\_size()] This method specifies the size of a
fp@369:   variable-sized PDO.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Device Class}
fp@369: \label{sec:class-device}
fp@369: \index{Device!Class}
fp@369: 
fp@369: The device class is responsible for communicating with the connected
fp@369: EtherCAT-enabled network driver. Figure~\ref{fig:uml-device} shows its
fp@369: UML class diagram.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.3\textwidth]{images/uml-device}
fp@369:   \caption{Device UML class diagram}
fp@369:   \label{fig:uml-device}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Device Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[master] A pointer to the master, which owns the device object.
fp@369: \item[dev] This is the pointer to the \textit{net\_device} structure
fp@369:   of the connected network device driver.
fp@369: \item[open] This flag stores, if the network device is ``opened'' and
fp@369:   ready for transmitting and receiving frames.
fp@369: \item[tx\_skb] The transmittion socket buffer. Instead of allocating a
fp@369:   new socket buffer for each frame, the same socket buffer is recycled
fp@369:   and used for every frame.
fp@369: \item[isr] The pointer to the network device's interrupt service
fp@369:   routine. \textit{ec\_isr\_t} is a type definition in the device
fp@369:   interface, which looks like below:
fp@369:   \begin{lstlisting}[gobble=4,language=C]
fp@369:     typedef irqreturn_t (*ec_isr_t)(int, void *,
fp@369:                                     struct pt_regs *);
fp@369:   \end{lstlisting}
fp@369: \item[module] A pointer to the network driver module, to increase and
fp@369:   decrease the use counter (see paragraph ``Implicit Dependencies'' in
fp@369:   section~\ref{sec:ecdev}).
fp@369: \item[link\_state] The current link state. It can be 0 ``down'' or 1
fp@369:   ``up''.
fp@369: \item[dbg] Every device objects contains a debugging interface (see
fp@369:   sectios~\ref{sec:class-debug} and~\ref{sec:debug}).
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Device Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_device\_init()] The device constructor.
fp@369: \item[ec\_device\_clear()] The device destructor.
fp@369: \item[ec\_device\_open()] ``Opens'' the device for transmittion and
fp@369:   reception of frames. This is equivalent to the \textit{ifconfig up}
fp@369:   command for ordinary Ethernet devices.
fp@369: \item[ec\_device\_close()] Stops frame transmittion and reception.
fp@369:   This is equivalent to the \textit{ifconfig down} command for
fp@369:   ordinary Ethernet devices.
fp@369: \item[ec\_device\_call\_isr()] Calls the interrupt service routine of
fp@369:   the device.
fp@369: \item[ec\_device\_tx\_data()] Returns a pointer into the memory of the
fp@369:   transmittion socket buffer \textit{tx\_skb}. This is used by the
fp@369:   master to assemble a new EtherCAT frame.
fp@369: \item[ec\_device\_send()] Sends an assembled frame by passing it to
fp@369:   the device's \textit{hard\_\-start\_\-xmit()} callback.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Device Methods (Device Interface)}
fp@369: 
fp@369: The device methods belonging to the device interface are explained in
fp@369: section~\ref{sec:ecdev}.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Datagram Class}
fp@369: \label{sec:class-datagram}
fp@369: \index{Datagram!Class}
fp@369: 
fp@369: So send and receive a datagram, an object of the
fp@369: \textit{ec\_datagram\_t} class is needed. It can be initialized with a
fp@369: datagram type \cite[section~5.4]{dlspec} and length (optionally filled
fp@369: with data) and appended to the master's datagram queue.
fp@369: Figure~\ref{fig:uml-datagram} shows its UML class diagram.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.3\textwidth]{images/uml-datagram}
fp@369:   \caption{Datagram UML class diagram}
fp@369:   \label{fig:uml-datagram}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Datagram Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[list] This attribute is needed to make a list of datagrams, as
fp@369:   used in the domain class (see section~\ref{sec:class-domain}).
fp@369: \item[queue] This attribute is the anchor to the master's datagram
fp@369:   queue, which is implemented as a linked list.
fp@369: \item[type] The datagram type. \textit{ec\_\-datagram\_\-type\_\-t} is
fp@369:   an enumeration, which can have the values
fp@369:   \textit{EC\_\-DATAGRAM\_\-APRD}, \textit{EC\_\-DATAGRAM\_\-APWR},
fp@369:   \textit{EC\_\-DATAGRAM\_\-NPRD}, \textit{EC\_\-DATAGRAM\_\-NPWR},
fp@369:   \textit{EC\_\-DATAGRAM\_\-BRD}, \textit{EC\_\-DATAGRAM\_\-BWR} or
fp@369:   \textit{EC\_\-DATAGRAM\_\-LRW}.
fp@369: \item[address] The slave address. For all addressing schemes take 4
fp@369:   bytes, \textit{ec\_address\_t} is a union type:
fp@369:   \begin{lstlisting}[gobble=4,language=C]
fp@369:     typedef union {
fp@369:             struct {
fp@369:                     uint16_t slave; /**< configured or
fp@369:                                          autoincrement
fp@369:                                          address */
fp@369:                     uint16_t mem; /**< physical memory
fp@369:                                        address */
fp@369:             } physical; /**< physical address */
fp@369:             uint32_t logical; /**< logical address */
fp@369:     } ec_address_t;
fp@369:   \end{lstlisting}
fp@369: \item[data] The actual data of the datagram. These are either filled
fp@369:   in before sending (at writing access) or are inserted by the
fp@369:   adressed slave(s) (at reading access). In any case, the data memory
fp@369:   must be dynamically allocated. Besides, this can be done before
fp@369:   cyclic processing with the \textit{ec\_datagram\_prealloc()} method
fp@369:   (see below).
fp@369: \item[mem\_size] The size of the allocated memory, \textit{data}
fp@369:   points to.
fp@369: \item[data\_size] The size of the actual data in the \textit{data}
fp@369:   memory.
fp@369: \item[index] The sequential EtherCAT datagram index. This value is set
fp@369:   by the master on sending, to easier assign a received datagram to a
fp@369:   queued datagram object.
fp@369: \item[working\_counter] The working counter of the datagram. This is
fp@369:   set to zero on sending and filled with the real value of the working
fp@369:   counter on datagram reception.
fp@369: \item[state] The state of the datagram.
fp@369:   \textit{ec\_\-datagram\_\-state\_\-t} is an enumeration and can be
fp@369:   \textit{EC\_\-DATA\-GRAM\_\-INIT},
fp@369:   \textit{EC\_\-DATA\-GRAM\_\-QUEU\-ED},
fp@369:   \textit{EC\_\-DATA\-GR\-AM\_\-SEN\-T},
fp@369:   \textit{EC\_\-DATA\-GRAM\_\-REC\-EIVED},
fp@369:   \textit{EC\_\-DATA\-GRAM\_\-TIMED\_\-OUT} or
fp@369:   \textit{EC\_\-DA\-TA\-GRAM\_\-ERR\-OR}.
fp@369: \item[t\_sent] This attribute is set to the timestamp, when the
fp@369:   datagram was sent, to later detect a timeout.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Datagram Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_datagram\_init()] The datagram's constructor.
fp@369: \item[ec\_datagram\_clear()] The datagram's destructor.
fp@369: \item[ec\_datagram\_prealloc()] Allocates memory for the datagram
fp@369:   data. This is especially needed, if the datagram structure will
fp@369:   later be used in a context, where no dynamic memory allocation is
fp@369:   allowed.
fp@369: \item[ec\_datagram\_nprd()] Initializes a ``Node-Addressed Physical
fp@369:   Read'' datagram \cite[section~5.4.1.2]{dlspec}.
fp@369: \item[ec\_datagram\_npwr()] Initializes a ``Node-Addressed Physical
fp@369:   Write'' datagram \cite[section~5.4.2.2]{dlspec}.
fp@369: \item[ec\_datagram\_aprd()] Initializes a ``Auto-Increment Physical
fp@369:   Read'' datagram \cite[section~5.4.1.1]{dlspec}.
fp@369: \item[ec\_datagram\_apwr()] Initializes a ``Auto-Increment Physical
fp@369:   Write'' datagram \cite[section~5.4.2.1]{dlspec}.
fp@369: \item[ec\_datagram\_brd()] Initializes a ``Broadcast Read'' datagram
fp@369:   \cite[section~5.4.1.3]{dlspec}.
fp@369: \item[ec\_datagram\_bwr()] Initializes a ``Broadcast Write'' datagram
fp@369:   \cite[section~5.4.2.3]{dlspec}.
fp@369: \item[ec\_datagram\_lrw()] Initializes a ``Logical ReadWrite''
fp@369:   datagram \cite[section~5.4.3.4]{dlspec}.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Domain Class}
fp@369: \label{sec:class-domain}
fp@369: \index{Domain!Class}
fp@369: 
fp@369: The domain class encapsules PDO registration and management of the
fp@369: process data image and its exchange. The UML class diagram can be seen
fp@369: in figure~\ref{fig:uml-domain}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.4\textwidth]{images/uml-domain}
fp@369:   \caption{Domain UML class diagram}
fp@369:   \label{fig:uml-domain}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Domain Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[kobj] This \textit{kobject} structure is needed for the Sysfs
fp@369:   representation of the domain.
fp@369: \item[list] The master manages a list of domains, so this list anchor
fp@369:   is needed.
fp@369: \item[index] The domain's index. The first domain will get index 0,
fp@369:   the second index 1, and so on.
fp@369: \item[master] A pointer to the master owning the domain.
fp@369: \item[data\_size] The size of the domain's process data image.
fp@369: \item[datagram] A linked list with the datagram objects, the domain
fp@369:   needs for process data exchange (see
fp@369:   section~\ref{sec:class-datagram}).
fp@369: \item[base\_address] This attribute stores the logical offset, to
fp@369:   which the domain's process data are mapped.
fp@369: \item[response\_count] The sum of the datagrams' working counters at
fp@369:   the last process data exchange. Changes are always reported.
fp@369: \item[data\_regs] The (linked) list of PDO registrations. The realtime
fp@369:   module requests the exchange of certain PDOs and supplies the
fp@369:   address of process data pointers, that will later point to the
fp@369:   respective locations in the process data image. These ``data
fp@369:   registrations'' are saved in the \textit{data\_regs} list.
fp@369: \item[working\_counter\_changes] This field stores the number of
fp@369:   working counter changes since the last notification. This helps to
fp@369:   reduce syslog output in case of frequent changes.
fp@369: \item[t\_last] The timestamp of the last working counter change
fp@369:   notification.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Domain Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_domain\_init()] The domain's constructor.
fp@369: \item[ec\_domain\_clear()] The domain's destructor.
fp@369: \item[ec\_domain\_alloc()] Allocates the process data image and the
fp@369:   respective datagrams based on the process data registrations.
fp@369: \item[ec\_domain\_queue()] Queues the domain's datagrams for exchange
fp@369:   via the master.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Private Domain Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_domain\_reg\_pdo\_entry()] This method is used to do a PDO
fp@369:   registration. It finds the appropriate sync manager covering the PDO
fp@369:   data, calculates its offset in the sync-manager-protected memory and
fp@369:   prepares the FMMU configurations for the related slave. Then the PDO
fp@369:   registration is appended to the list.
fp@369: \item[ec\_domain\_clear\_data\_regs()] Clearing all process data
fp@369:   registrations is needed in serveral places and therefore has been
fp@369:   sourced out to an own method.
fp@369: \item[ec\_domain\_add\_datagram()] This methods allocates a datagram
fp@369:   and appends it to the list. This is done during domain allocation.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Domain Methods (Realtime Interface)}
fp@369: 
fp@369: The domain methods belonging to the realtime interface are introduced
fp@369: in section~\ref{sec:ecrt-domain}.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Finite State Machine Class}
fp@369: \label{sec:class-fsm}
fp@369: \index{FSM!Class}
fp@369: 
fp@369: This class encapsules all state machines, except the EoE state
fp@369: machine. Its UML class diagram can be seen in
fp@369: figure~\ref{fig:uml-fsm}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/uml-fsm}
fp@369:   \caption{Finite State Machine UML class diagram}
fp@369:   \label{fig:uml-fsm}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{FSM Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[master] A pointer to the master owning the FSM object.
fp@369: \item[slave] Serveral sub state machines are executed for single
fp@369:   slaves. This pointer stores the current slave for these FSMs.
fp@369: \item[datagram] The FSM class has its own datagram, which is used in
fp@369:   every state and sub-state.
fp@369: \item[master\_state] This function pointer stores the current state
fp@369:   function for one of the master's state machines.
fp@369: \item[master\_slaves\_responding] This attribute is used in the
fp@369:   operation state machine (see section~\ref{sec:fsm-op}) to store the
fp@369:   number of slaves, that responded to the last broadcast command.
fp@369: \item[master\_slave\_states] This attribute stores the slave states,
fp@369:   that were determined by the last broadcast command.
fp@369: \item[master\_validation] This flag is used by the operation state
fp@369:   machine and is non-zero, if a bus validation has to be done.
fp@369: \item[slave\_state] This function pointer stores the current state of
fp@369:   the slave scan state machine (see section~\ref{sec:fsm-scan}) or the
fp@369:   slave configuration state machine (see section~\ref{sec:fsm-conf}).
fp@369: \item[sii\_state] This function pointer stores the current state of
fp@369:   the SII state machine (see section~\ref{sec:fsm-sii}).
fp@369: \item[sii\_offset] This attribute is used by the SII state machine to
fp@369:   store the word address for the current read or write cycle.
fp@369: \item[sii\_mode] If this attribute is zero, the SII access is done
fp@369:   with ``auto-increment'' datagrams \cite[section~5.4]{dlspec}.
fp@369:   If it is non-zero, ``station-address'' datagrams are used.
fp@369: \item[sii\_value] This attribute stores the value to write, or the
fp@369:   read value, respectively.
fp@369: \item[sii\_start] A timestamp attribute, that stores the beginning
fp@369:   time of an SII operation to detect a timeout.
fp@369: \item[change\_state] This function pointer stores the current state of
fp@369:   the state change state machine.
fp@369: \item[change\_new] This attribute stores the requested state for the
fp@369:   state change state machine.
fp@369: \item[change\_start] A timestamp attribute to detect a timeout while
fp@369:   changing slave states.
fp@369: \item[coe\_state] This function pointer stores the current state of
fp@369:   the CoE state machines.
fp@369: \item[sdodata] This is an SDO data object that stores information
fp@369:   about the current SDO to write.
fp@369: \item[coe\_start] A timestamp attribute to detect timeouts during CoE
fp@369:   configuration.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public FSM Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_fsm\_init()] Constructor of the FSM class.
fp@369: \item[ec\_fsm\_clear()] Destructor of the FSM class.
fp@369: \item[ec\_fsm\_reset()] Resets the whole FSM object. This is needed to
fp@369:   restart the master state machines.
fp@369: \item[ec\_fsm\_execute()] Executes one state of the current state
fp@369:   machine and then returns.
fp@369: \item[ec\_fsm\_startup()] Initializes the master startup state
fp@369:   machine, which determines the number of slaves and executes the
fp@369:   slave scan state machine for each slave.
fp@369: \item[ec\_fsm\_startup\_running()] Returns non-zero, if the startup
fp@369:   state machine did not terminate yet.
fp@369: \item[ec\_fsm\_startup\_success()] Returns non-zero, if the startup
fp@369:   state machine terminated with success.
fp@369: \item[ec\_fsm\_configuration()] Initializes the master configuration
fp@369:   state machine, which executes the slave configuration state machine
fp@369:   for each slave.
fp@369: \item[ec\_fsm\_configuration\_running()] Returns non-zero, if the
fp@369:   configuration state machine did not terminate yet.
fp@369: \item[ec\_fsm\_configuration\_success()] Returns non-zero, if the
fp@369:   configuration state machine terminated with success.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{FSM State Methods}
fp@369: 
fp@369: The rest of the methods showed in the UML class diagram are state
fp@369: methods of the state machines. These states are described in
fp@369: section~\ref{sec:fsm}.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The EoE Class}
fp@369: \label{sec:class-eoe}
fp@369: \index{EoE!Class}
fp@369: 
fp@369: Objects of the \textit{ec\_eoe\_t} class are called EoE handlers. Each
fp@369: EoE handler represents a virtual network interface and can be coupled
fp@369: to a EoE-capable slave on demand. The UML class diagram can be seen in
fp@369: figure~\ref{fig:uml-eoe}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.4\textwidth]{images/uml-eoe}
fp@369:   \caption{EoE UML class diagram}
fp@369:   \label{fig:uml-eoe}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{EoE Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[list] The master class maintains a list of EoE handlers.
fp@369:   Therefore this list anchor is needed.
fp@369: \item[slave] If an EoE handler is coupled to a slave, this pointer
fp@369:   points to the related slave object. Otherwise it is \textit{NULL}.
fp@369: \item[datagram] Every EoE handler owns a datagram object to exchange
fp@369:   data with the coupled slave via its state machine.
fp@369: \item[state] This function pointer points to the current state of the
fp@369:   EoE state machine (see section~\ref{sec:eoeimp}).
fp@369: \item[dev] A pointer to the \textit{net\_device} structure that
fp@369:   represents the network interface to the kernel.
fp@369: \item[stats] The statistics object for the network interface.
fp@369: \item[opened] This flag stores, if the network interface was opened.
fp@369:   No EoE processing will be done, if the device is not opened.
fp@369: \item[t\_last] This timestamp attribute stores the time of the last
fp@369:   bit rate measurement.
fp@369: \item[rx\_skb] A pointer to the current receive socket buffer. On
fp@369:   every first fragment of a received frame, a new receive socket
fp@369:   buffer is allocated. On every last fragment, this buffer will be
fp@369:   passed to the network stack.
fp@369: \item[rx\_skb\_offset] This attribute stores the offset for the next
fp@369:   fragment data in the receive socket buffer.
fp@369: \item[rx\_skb\_size] This attribute stores the current data size of
fp@369:   the receive socket buffer.
fp@369: \item[rx\_expected\_fragment] The expected number of the next
fp@369:   fragment. If a fragment with an invalid number is received, the
fp@369:   whole frame will be dropped.
fp@369: \item[rx\_counter] This is the sum of the octets received since the
fp@369:   last bit rate measurement.
fp@369: \item[rx\_rate] This attribute stores the receive bit rate in bps.
fp@369: \item[tx\_queue] Each EoE handler maintains a transmittion queue for
fp@369:   frames, that come in via the network interface. This queue is
fp@369:   implemented with a linked list and protected by a spinlock.
fp@369: \item[tx\_queue\_active] This flag stores, if the transmittion queue
fp@369:   is currently accepting frames from the network stack. If the queue
fp@369:   gets filled up, frame transmittion is suspended with a call to
fp@369:   \textit{netif\_stop\_queue()}. If the fill state decreases below the
fp@369:   half capacity, frame transmittion is restarted with
fp@369:   \textit{netif\_wake\_queue()}.
fp@369: \item[tx\_queued\_frames] The number of frames in the transmittion
fp@369:   queue.
fp@369: \item[tx\_queue\_lock] The spinlock used to protect the transmittion
fp@369:   queue. This is needed, because the queue is accessed both from
fp@369:   network stack context and from the master's EoE timer.
fp@369: \item[tx\_frame] The frame that is currently sent. The
fp@369:   \textit{ec\_eoe\_frame\_t} structure combines the socket buffer
fp@369:   structure with a list head to append it to the transmittion queue.
fp@369: \item[tx\_frame\_number] The EoE protocol demands to maintain a
fp@369:   sequencial frame number, that must be increased with every frame
fp@369:   sent.
fp@369: \item[tx\_fragment\_number] The sequencial number of the next fragment
fp@369:   to transmit.
fp@369: \item[tx\_offset] Current frame data offset for the next fragment to
fp@369:   transmit.
fp@369: \item[tx\_counter] The number of octets transferred since the last bit
fp@369:   rate measurement.
fp@369: \item[tx\_rate] The recent transmittion bit rate in bps.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public EoE Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_eoe\_init()] The EoE handler's constructor. The network
fp@369:   interface is allocated and registered.
fp@369: \item[ec\_eoe\_clear()] The EoE handler's destructor. The network
fp@369:   interface is unregistered and all allocated memory is freed.
fp@369: \item[ec\_eoe\_run()] Executes the EoE state machine (see
fp@369:   section~\ref{sec:eoeimp}) for this handler.
fp@369: \item[ec\_eoe\_active()] Returns true, if the handler has a slave
fp@369:   coupled and the network interface is opened.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Private EoE Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_eoe\_flush()] Clears the transmittion queue and drops all
fp@369:   frames queued for sending.
fp@369: \item[ec\_eoe\_send()] Sends one fragment of the current frame.
fp@369: \end{description}
fp@369: 
fp@369: 
fp@369: \paragraph{EoE State Methods}
fp@369: 
fp@369: The rest of the private methods are state functions for the EoE state
fp@369: machine, which is discussed in section~\ref{sec:eoeimp}.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{The Debug Class}
fp@369: \label{sec:class-debug}
fp@369: 
fp@369: The debug class maintains a virtual network interface. All frames that
fp@369: are sent and received by the master will be forwarded to this network
fp@369: interface, so that bus monitoring can be done with third party tools
fp@369: (see section~\ref{sec:debug}). Figure~\ref{fig:uml-debug} shows the
fp@369: UML class diagram.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.3\textwidth]{images/uml-debug}
fp@369:   \caption{Debug UML class diagram}
fp@369:   \label{fig:uml-debug}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Debug Attributes}
fp@369: 
fp@369: \begin{description}
fp@369: \item[dev] A pointer to the allocated \textit{net\_device} structure
fp@369:   that represents the network interface in the kernel.
fp@369: \item[stats] An object for interface statistics.
fp@369: \item[opened] Stores the state of the device. Frames will only be
fp@369:   forwarded, if the device was opened with the \textit{ifconfig up}
fp@369:   command (or something similar).
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Public Debug Methods}
fp@369: 
fp@369: \begin{description}
fp@369: \item[ec\_debug\_init()] The constructor.
fp@369: \item[ec\_debug\_clear()] The destructor.
fp@369: \item[ec\_debug\_send()] This method forwards a frame to the virtual
fp@369:   network interface. It dynamically allocates a new socket buffer and
fp@369:   passes it to the network stack.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Realtime Interface}
fp@369: \label{sec:ecrt}
fp@369: \index{Realtime interface}
fp@369: 
fp@369: The realtime interface provides functions and data structures for
fp@369: realtime modules to access and use an EtherCAT master.
fp@369: 
fp@369: \subsubsection{Master Requesting and Releasing}
fp@369: 
fp@369: Before a realtime module can access am EtherCAT master provided by the
fp@369: master module, it has to reserve one for exclusive use. After use, it
fp@369: has to release the requested master and make it available for other
fp@369: modules. This is done with the following functions:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   ec_master_t *ecrt_request_master(unsigned int master_index);
fp@369:   void ecrt_release_master(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_request\_master()} function has to be the first
fp@369: function a module has to call, when using EtherCAT. The function takes
fp@369: the index of the master as its argument. The first master has index 0,
fp@369: the $n$th master has index $n - 1$. The number of existent masters has
fp@369: to be specified when loading the master module (see
fp@369: section~\ref{sec:mastermod}). The function tries to reserve the
fp@369: specified master and scans for slaves. It returns a pointer to the
fp@369: reserved master object upon success, or \textit{NULL} if an error
fp@369: occured.
fp@369: 
fp@369: The \textit{ecrt\_release\_master()} function releases a reserved
fp@369: master after use. It takes the pointer to the master object returned
fp@369: by \textit{ecrt\_request\_master()} as its argument and can never
fp@369: fail.
fp@369: 
fp@369: \subsubsection{Master Methods}
fp@369: \label{sec:ecrt-master}
fp@369: 
fp@369: \paragraph{Domain Creation}
fp@369: 
fp@369: For process data exchange, at least one process data domain is needed
fp@369: (see section~\ref{sec:processdata}).
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   ec_domain_t *ecrt_master_create_domain(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_master\_create\_domain()} method creates a new
fp@369: process data domain and returns a pointer to the new domain object.
fp@369: This object can be used for registering process data objects and
fp@369: exchange process data in cyclic operation. On failure, the function
fp@369: returns \textit{NULL}.
fp@369: 
fp@369: \paragraph{Slave Handlers}
fp@369: 
fp@369: To access a certain slave, there is a method to get a slave handler:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   ec_slave_t *ecrt_master_get_slave(const ec_master_t *,
fp@369:                                     const char *);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_master\_get\_slave()} method returns a pointer to a
fp@369: certain slave object, specified by its ASCII address (see
fp@369: section~\ref{sec:addr}). If the address is invalid, \textit{NULL} is
fp@369: returned.
fp@369: 
fp@369: \paragraph{Master Activation}
fp@369: 
fp@369: When all domains are created, and all process data objects are
fp@369: registered, the master can be activated:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecrt_master_activate(ec_master_t *master);
fp@369:   void ecrt_master_deactivate(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: By calling the \textit{ecrt\_master\_activate()} method, all slaves
fp@369: are configured according to the prior method calls and are brought
fp@369: into \textit{OP} state. In this case, the method has a return value of
fp@369: 0. Otherwise (wrong configuration or bus failure) the method returns
fp@369: non-zero.
fp@369: 
fp@369: The \textit{ecrt\_master\_deactivate()} method is the counterpart to
fp@369: the activate call: It brings all slaves back into \textit{INIT} state
fp@369: again. This method should be called prior to
fp@369: \textit{ecrt\_\-master\_\-release()}.
fp@369: 
fp@369: \paragraph{Locking Callbacks}
fp@369: 
fp@369: For concurrent master access, the realtime module has to provide a
fp@369: locking mechanism (see section~\ref{sec:concurr}):
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecrt_master_callbacks(ec_master_t *master,
fp@369:                              int (*request_cb)(void *),
fp@369:                              void (*release_cb)(void *),
fp@369:                              void *cb_data);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The ``request lock'' and ``release lock'' callbacks can be set with
fp@369: the \textit{ecrt\_master\_call\-backs()} method. It takes two function
fp@369: pointers and a data value as additional arguments. The arbitrary data
fp@369: value will be passed as argument on every callback. Asynchronous
fp@369: master access (like EoE processing) is only possible if these
fp@369: callbacks have been set.
fp@369: 
fp@369: \paragraph{Preparation of Cyclic Data Exchange}
fp@369: 
fp@369: Cyclic operation mostly consists of the three steps input, processing
fp@369: and output. In EtherCAT terms this would mean: Receive datagrams,
fp@369: evaluate process data and send datagrams. The first cycle differs from
fp@369: this principle, because no datagrams have been sent yet, so there is
fp@369: nothing to receive. To avoid having a case differantiation (in terms
fp@369: of an \textit{if} clause), the following method exists:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecrt_master_prepare(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: As a last thing before cyclic operation, a call to the
fp@369: \textit{ecrt\_master\_prepare()} method should be issued. It makes all
fp@369: process data domains queue their datagrams and issues a send command,
fp@369: so that the first receive call in cyclic operation will not fail.
fp@369: 
fp@369: \paragraph{Frame Sending and Receiving}
fp@369: 
fp@369: To send all queued datagrams and to later receive the sent datagrams
fp@369: there are two methods:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecrt_master_send(ec_master_t *master);
fp@369:   void ecrt_master_receive(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_master\_send()} method takes all datagrams, that
fp@369: have been queued for transmission, packs them into frames, and passes
fp@369: them to the network device for sending.
fp@369: 
fp@369: The \textit{ecrt\_master\_receive()} queries the network device for
fp@369: received frames (by calling the ISR\index{ISR}), extracts received
fp@369: datagrams and dispatches the results to the datagram objects in the
fp@369: queue. Received datagrams, and the ones that timed out, will be
fp@369: marked, and then dequeued.
fp@369: 
fp@369: \paragraph{Running the Operation State Machine}
fp@369: 
fp@369: The master's operation state machine (see section~\ref{sec:fsm-op})
fp@369: monitors the bus in cyclic operation and reconfigures slaves, if
fp@369: necessary. Therefore, the following method should be called
fp@369: cyclically:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecrt_master_run(ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_master\_run()} method executes the master's
fp@369: operation state machine step by step. It returns after processing one
fp@369: state and queuing a datagram. Calling this function is not mandatory,
fp@369: but highly recommended.
fp@369: 
fp@369: \paragraph{Master Monitoring}
fp@369: 
fp@369: It is also highly recommended to evaluate the master's error state. In
fp@369: this way it is possible to notice lost network links, failed bus
fp@369: segments, and other issues:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecrt_master_state(const ec_master_t *master);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_master\_state()} method returns the master's error
fp@369: state. The following states are defined as part of the realtime
fp@369: interface:
fp@369: 
fp@369: \begin{description}
fp@369: \item[EC\_MASTER\_OK] means, that no error has occurred.
fp@369: \item[EC\_MASTER\_LINK\_ERROR] means, that the network link is
fp@369:   currently down.
fp@369: \item[EC\_MASTER\_BUS\_ERROR] means, that one or more slaves do not
fp@369:   respond.
fp@369: \end{description}
fp@369: 
fp@369: \subsubsection{Domain Methods}
fp@369: \label{sec:ecrt-domain}
fp@369: 
fp@369: \paragraph{PDO Registration}
fp@369: 
fp@369: To access data of a slave's PDO in cyclic operation, it is necessary
fp@369: to make it part of a process data domain:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   ec_slave_t *ecrt_domain_register_pdo(ec_domain_t *domain,
fp@369:                                        const char *address,
fp@369:                                        uint32_t vendor_id,
fp@369:                                        uint32_t product_code,
fp@369:                                        const char *pdo_name
fp@369:                                        void **data_ptr);
fp@369:   int ecrt_domain_register_pdo_list(ec_domain_t *domain,
fp@369:                                     const ec_pdo_reg_t *pdos);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_domain\_register\_pdo()} method registers a certain
fp@369: PDO as part of the domain and takes the address of the process data
fp@369: pointer. This pointer will be set on master activation and then can be
fp@369: parameter to the \textit{EC\_READ\_*} and \textit{EC\_WRITE\_*} macros
fp@369: described below.
fp@369: 
fp@369: A perhaps easier way to register multiple PDOs at the same time is to
fp@369: fill an array of \textit{ec\_pdo\_reg\_t} and hand it to the
fp@369: \textit{ecrt\_domain\_register\_pdo\_list()} method. Attention: This
fp@369: array has to be terminated by an empty structure (\textit{\{\}})!
fp@369: 
fp@369: \paragraph{Evaluating Domain Data}
fp@369: 
fp@369: To evaluate domain data, the following method has to be used:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   void ecrt_domain_process(ec_domain_t *domain);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_domain\_process()} method sets the domains state and
fp@369: requeues its datagram for sending.
fp@369: 
fp@369: \paragraph{Domain State}
fp@369: 
fp@369: Similar to the master state, a domain has an own error state:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecrt_domain_state(const ec_domain_t *domain);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_domain\_state()} method returns the domain's error
fp@369: state. It is non-zero if \underline{not} all process data values could
fp@369: be exchanged, and zero otherwise.
fp@369: 
fp@369: \subsubsection{Slave Methods}
fp@369: \label{sec:ecrt-slave}
fp@369: 
fp@369: \paragraph{SDO Configuration}
fp@369: 
fp@369: To configure slave SDOs, the function interface below can be used:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecrt_slave_conf_sdo8(ec_slave_t *slave,
fp@369:                            uint16_t sdo_index,
fp@369:                            uint8_t sdo_subindex,
fp@369:                            uint8_t value);
fp@369:   int ecrt_slave_conf_sdo16(ec_slave_t *slave,
fp@369:                             uint16_t sdo_index,
fp@369:                             uint8_t sdo_subindex,
fp@369:                             uint16_t value);
fp@369:   int ecrt_slave_conf_sdo32(ec_slave_t *slave,
fp@369:                             uint16_t sdo_index,
fp@369:                             uint8_t sdo_subindex,
fp@369:                             uint32_t value);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_slave\_conf\_sdo*()} methods prepare the
fp@369: configuration of a certain SDO. The index and subindex of the SDO, and
fp@369: the value have to be specified. The configuration is done each time,
fp@369: the slave is reconfigured. The methods only differ in the SDO's data
fp@369: type. If the configuration could be prepared, zero is returned. If an
fp@369: error occured, non-zero is returned.
fp@369: 
fp@369: \paragraph{Variable-sized PDOs}
fp@369: 
fp@369: For specifying the size of variable-sized PDOs, the following method
fp@369: can be used:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   int ecrt_slave_pdo_size(ec_slave_t *slave,
fp@369:                           const char *pdo_name,
fp@369:                           size_t size);
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ecrt\_slave\_pdo\_size()} method takes the name of the PDO
fp@369: and the size. It returns zero on success, otherwise non-zero.
fp@369: 
fp@369: \subsubsection{Process Data Access}
fp@369: \label{sec:macros}
fp@369: 
fp@369: The endianess of the process data could differ from that of the CPU.
fp@369: Therefore, process data access has to be done by the macros below,
fp@369: that are also provided by the realtime interface:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   #define EC_READ_BIT(DATA, POS)
fp@369:   #define EC_WRITE_BIT(DATA, POS, VAL)
fp@369: 
fp@369:   #define EC_READ_U8(DATA)
fp@369:   #define EC_READ_S8(DATA)
fp@369:   #define EC_READ_U16(DATA)
fp@369:   #define EC_READ_S16(DATA)
fp@369:   #define EC_READ_U32(DATA)
fp@369:   #define EC_READ_S32(DATA)
fp@369: 
fp@369:   #define EC_WRITE_U8(DATA, VAL)
fp@369:   #define EC_WRITE_S8(DATA, VAL)
fp@369:   #define EC_WRITE_U16(DATA, VAL)
fp@369:   #define EC_WRITE_S16(DATA, VAL)
fp@369:   #define EC_WRITE_U32(DATA, VAL)
fp@369:   #define EC_WRITE_S32(DATA, VAL)
fp@369: \end{lstlisting}
fp@369: 
fp@369: There are macros for bitwise access (\textit{EC\_READ\_BIT()},
fp@369: \textit{EC\_WRITE\_BIT()}), and bytewise access
fp@369: (\textit{EC\_READ\_*()}, \textit{EC\_WRITE\_*()}). The bytewise macros
fp@369: carry the data type in their name. Example: \textit{EC\_WRITE\_S16()}
fp@369: writes a 16 bit signed value to EtherCAT data. The \textit{DATA}
fp@369: parameter is supposed to be a process data pointer, as provided at PDO
fp@369: registration.
fp@369: 
fp@369: The macros use the kernel's endianess conversion macros, that are
fp@369: preprocessed to empty macros in case of equal endianess. This is the
fp@369: definition for the \textit{EC\_\-READ\_\-U16()} macro:
fp@369: 
fp@369: \begin{lstlisting}[language=C]
fp@369:   #define EC_READ_U16(DATA) \
fp@369:           ((uint16_t) le16_to_cpup((void *) (DATA)))
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{le16\_to\_cpup()} macro converts a little-endian, 16 bit
fp@369: value to the CPU's architecture and takes a pointer to the input value
fp@369: as its argument. If the CPU's architecture is little-endian, too (for
fp@369: example on X86 and compatible), nothing has to be converted. In this
fp@369: case, the macro is replaced with an empty macro by the preprocessor
fp@369: and so there is no unneeded function call or case differentiation in
fp@369: the code.
fp@369: 
fp@369: For keeping it portable, it is highly recommended to make use of these
fp@369: macros.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Slave Addressing}
fp@369: \label{sec:addr}
fp@369: \index{Slave!Addressing}
fp@369: 
fp@369: The master offers the serveral slave addressing schemes (for PDO
fp@369: registration or configuration) via the realtime interface. For this
fp@369: reason, slave addresses are ASCII\nomenclature{ASCII}{American
fp@369:   Standard Code for Information Interchange}-coded and passed as a
fp@369: string. The addressing schemes are independent of the EtherCAT
fp@369: protocol and represent an additional feature of the master.
fp@369: 
fp@369: Below, the allowed addressing schemes are described. The descriptions
fp@369: are followed by a regular expression formally defining the addressing
fp@369: scheme, and one or more examples.
fp@369: 
fp@369: \begin{description}
fp@369: \item[Position Addressing] This is the normal addressing scheme, where
fp@369:   each slave is addressed by its ring position. The first slave has
fp@369:   address 0, and the $n$th slave has address $n - 1$. This addressing
fp@369:   scheme is useful for small busses that have a fixed number of slaves.\\
fp@369:   RegEx: \texttt{[0-9]+} --- Example: \texttt{"42"}
fp@369: \item[Advanced Position Addressing] Bus couplers segment the bus into
fp@369:   (physical) blocks. Though the logical ring positions keep being the
fp@369:   same, it is easier to address a slave with its block number and the
fp@369:   relative position inside the block. This addressing is done by
fp@369:   passing the (zero-based) index of the bus coupler (not the coupler's
fp@369:   ring position), followed by a colon and the relative position of the
fp@369:   actual slave starting at the bus coupler.\\
fp@369:   RegEx: \texttt{[0-9]+:[0-9]+} --- Examples: \texttt{"0:42"},
fp@369:   \texttt{"2:7"}
fp@369: \item[Alias Addressing] Each slave can have a ``secondary slave
fp@369:   address'' or ``alias address''\footnote{Information about how to set
fp@369:     the alias can be found in section~\ref{sec:eepromaccess}} stored
fp@369:   in its E$^2$PROM.  The alias is evaluated by the master and can be
fp@369:   used to address the slave, which is useful when a clearly defined
fp@369:   slave has to be addressed and the ring position is not known or can
fp@369:   change over time. This scheme is used by starting the address string
fp@369:   with a mesh (\#) followed by the alias address.  The latter can also
fp@369:   be provided as hexadecimal value, prefixed with \textit{0x}.\\
fp@369:   RegEx: \texttt{\#(0x[0-9A-F]+|[0-9]+)} --- Examples:
fp@369:   \texttt{"\#6622"}, \texttt{"\#0xBEEF"}
fp@369: \item[Advanced Alias Addressing] This is a mixture of the ``Alias
fp@369:   Addressing'' and ``Advanced Position Addressing'' schemes. A certain
fp@369:   slave is addressed by specifying its relative position after an
fp@369:   aliased slave. This is very useful, if a complete block of slaves
fp@369:   can vary its position in the bus. The bus coupler preceeding the
fp@369:   block should get an alias. The block slaves can then be addressed by
fp@369:   specifying this alias and their position inside the block. This
fp@369:   scheme is used by starting the address string with a mesh (\#)
fp@369:   followed by the alias address (which can be hexadecimal), then a
fp@369:   colon and the relative posision of the slave to
fp@369:   address.\\
fp@369:   RegEx: \texttt{\#(0x[0-9A-F]+|[0-9]+):[0-9]+} --- Examples:
fp@369:   \texttt{"\#0xBEEF:7"}, \texttt{"\#6:2"}
fp@369: \end{description}
fp@369: 
fp@369: In anticipation of section~\ref{sec:ecrt}, the functions accepting
fp@369: these address strings are \textit{ecrt\_\-master\_\-get\_slave()},
fp@369: \textit{ecrt\_domain\_register\_pdo()} and
fp@369: \textit{ecrt\_domain\_register\_pdo\_list()} (the latter through the
fp@369: \textit{ec\_pdo\_reg\_t} structure).
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Concurrent Master Access}
fp@369: \label{sec:concurr}
fp@369: \index{Concurrency}
fp@369: 
fp@369: In some cases, one master is used by serveral instances, for example
fp@369: when a realtime module does cyclic process data exchange, and there
fp@369: are EoE-capable slaves that require to exchange Ethernet data with the
fp@369: kernel (see section~\ref{sec:eoeimp}). For this reason, the master is
fp@369: a shared resource, and access to it has to be sequenctialized. This is
fp@369: usually done by locking with semaphores, or other methods to protect
fp@369: critical sections.
fp@369: 
fp@369: The master itself can not provide locking mechanisms, because it has
fp@369: no chance to know the appropriate kind of lock. Imagine, the realtime
fp@369: module uses RTAI functionality, then ordinary kernel semaphores would
fp@369: not be sufficient. For that, an important design decision was made:
fp@369: The realtime module that reserved a master must have the total
fp@369: control, therefore it has to take responsibility for providing the
fp@369: appropriate locking mechanisms. If another instance wants to access
fp@369: the master, it has to request the master lock by callbacks, that have
fp@369: to be set by the realtime module. Moreover the realtime module can
fp@369: deny access to the master if it consideres it to be awkward at the
fp@369: moment.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.6\textwidth]{images/master-locks}
fp@369:   \caption{Concurrent master access}
fp@369:   \label{fig:locks}
fp@369: \end{figure}
fp@369: 
fp@369: Figure~\ref{fig:locks} exemplary shows, how two processes share one
fp@369: master: The realtime module's cyclic thread uses the master for
fp@369: process data exchange, while the master-internal EoE process uses it
fp@369: to communicate with EoE-capable slaves. Both have to aquire the master
fp@369: lock before access: The realtime thread can access the lock natively,
fp@369: while the EoE process has to use the master callbacks.
fp@369: Section~\ref{sec:concurrency} gives an example, of how to implement
fp@369: this.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{The Master's State Machines}
fp@369: \label{sec:fsm}
fp@369: \index{FSM}
fp@369: 
fp@369: Many parts of the EtherCAT master are implemented as \textit{finite
fp@369:   state machines} (FSMs\nomenclature{FSM}{Finite State Machine}).
fp@369: Though this leads to a higher grade of complexity in some aspects, is
fp@369: opens many new possibilities.
fp@369: 
fp@369: The below short code example exemplary shows how to read all slave
fp@369: states and moreover illustrates the restrictions of ``sequential''
fp@369: coding:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram
fp@369:   if (ec_master_simple_io(master, datagram)) return -1;
fp@369:   slave_states = EC_READ_U8(datagram->data); // process datagram
fp@369: \end{lstlisting}
fp@369: 
fp@369: The \textit{ec\_master\_simple\_io()} function provides a simple
fp@369: interface for synchronously sending a single datagram and receiving
fp@369: the result\footnote{For all communication issues have been meanwhile
fp@369:   sourced out into state machines, the function is deprecated and
fp@369:   stopped existing. Nevertheless it is adequate for showing it's own
fp@369:   restrictions.}. Internally, it queues the specified datagram,
fp@369: invokes the \textit{ec\_master\_send\_datagrams()} function to send a
fp@369: frame with the queued datagram and then waits actively for its
fp@369: reception.
fp@369: 
fp@369: This sequential approach is very simple, reflecting in only three
fp@369: lines of code. The disadvantage is, that the master is blocked for the
fp@369: time it waits for datagram reception. There is no difficulty when only
fp@369: one instance is using the master, but if more instances want to
fp@369: (synchronously\footnote{At this time, synchronous master access will
fp@369:   be adequate to show the advantages of an FSM. The asynchronous
fp@369:   approach will be discussed in section~\ref{sec:eoeimp}}) use the
fp@369: master, it is inevitable to think about an alternative to the
fp@369: sequential model.
fp@369: 
fp@369: Master access has to be sequentialized for more than one instance
fp@369: wanting to send and receive datagrams synchronously. With the present
fp@369: approach, this would result in having one phase of active waiting for
fp@369: each instance, which would be non-acceptable especially in realtime
fp@369: circumstances, because of the huge time overhead.
fp@369: 
fp@369: A possible solution is, that all instances would be executed
fp@369: sequentially to queue their datagrams, then give the control to the
fp@369: next instance instead of waiting for the datagram reception. Finally,
fp@369: bus IO is done by a higher instance, which means that all queued
fp@369: datagrams are sent and received. The next step is to execute all
fp@369: instances again, which then process their received datagrams and issue
fp@369: new ones.
fp@369: 
fp@369: This approach results in all instances having to retain their state,
fp@369: when giving the control back to the higher instance. It is quite
fp@369: obvious to use a \textit{finite state machine} model in this case.
fp@369: Section~\ref{sec:fsmtheory} will introduce some of the theory used,
fp@369: while the listings below show the basic approach by coding the example
fp@369: from above as a state machine:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   // state 1
fp@369:   ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram
fp@369:   ec_master_queue(master, datagram); // queue datagram
fp@369:   next_state = state_2;
fp@369:   // state processing finished
fp@369: \end{lstlisting}
fp@369: 
fp@369: After all instances executed their current state and queued their
fp@369: datagrams, these are sent and received. Then the respective next
fp@369: states are executed:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   // state 2
fp@369:   if (datagram->state != EC_DGRAM_STATE_RECEIVED) {
fp@369:           next_state = state_error;
fp@369:           return; // state processing finished
fp@369:   }
fp@369:   slave_states = EC_READ_U8(datagram->data); // process datagram
fp@369:   // state processing finished.
fp@369: \end{lstlisting}
fp@369: 
fp@369: See section~\ref{sec:statemodel} for an introduction to the
fp@369: state machine programming concept used in the master code.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{State Machine Theory}
fp@369: \label{sec:fsmtheory}
fp@369: \index{FSM!Theory}
fp@369: 
fp@369: A finite state machine \cite{automata} is a model of behavior with
fp@369: inputs and outputs, where the outputs not only depend on the inputs,
fp@369: but the history of inputs. The mathematical definition of a finite
fp@369: state machine (or finite automaton) is a six-tuple $(\Sigma, \Gamma,
fp@369: S, s_0, \delta, \omega)$, with
fp@369: 
fp@369: \begin{itemize}
fp@369: \item the input alphabet $\Sigma$, with $\Sigma \neq
fp@369:   \emptyset$, containing all input symbols,
fp@369: \item the output alphabet $\Gamma$, with $\Gamma \neq
fp@369:   \emptyset$, containing all output symbols,
fp@369: \item the set of states $S$, with $S \neq \emptyset$,
fp@369: \item the set of initial states $s_0$ with $s_0 \subseteq S, s_0 \neq
fp@369:   \emptyset$
fp@369: \item the transition function $\delta: S \times \Sigma \rightarrow S
fp@369:   \times \Gamma$
fp@369: \item the output function $\omega$.
fp@369: \end{itemize}
fp@369: 
fp@369: The state transition function $\delta$ is often specified by a
fp@369: \textit{state transition table}, or by a \textit{state transition
fp@369:   diagram}. The transition table offers a matrix view of the state
fp@369: machine behavior (see table~\ref{tab:statetrans}). The matrix rows
fp@369: correspond to the states ($S = \{s_0, s_1, s_2\}$) and the columns
fp@369: correspond to the input symbols ($\Gamma = \{a, b, \varepsilon\}$).
fp@369: The table contents in a certain row $i$ and column $j$ then represent
fp@369: the next state (and possibly the output) for the case, that a certain
fp@369: input symbol $\sigma_j$ is read in the state $s_i$.
fp@369: 
fp@369: \begin{table}[htbp]
fp@369:   \caption{A typical state transition table}
fp@369:   \label{tab:statetrans}
fp@369:   \vspace{2mm}
fp@369:   \centering
fp@369:   \begin{tabular}{l|ccc}
fp@369:     & $a$ & $b$ & $\varepsilon$\\ \hline
fp@369:     $s_0$ & $s_1$ & $s_1$ & $s_2$\\
fp@369:     $s_1$ & $s_2$ & $s_1$ & $s_0$\\
fp@369:     $s_2$ & $s_0$ & $s_0$ & $s_0$\\ \hline
fp@369:   \end{tabular}
fp@369: \end{table}
fp@369: 
fp@369: The state diagram for the same example looks like the one in
fp@369: figure~\ref{fig:statetrans}. The states are represented as circles or
fp@369: ellipses and the transitions are drawn as arrows between them. Close
fp@369: to a transition arrow can be the condition that must be fulfilled to
fp@369: allow the transition. The initial state is marked by a filled black
fp@369: circle with an arrow pointing to the respective state.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.5\textwidth]{images/statetrans}
fp@369:   \caption{A typical state transition diagram}
fp@369:   \label{fig:statetrans}
fp@369: \end{figure}
fp@369: 
fp@369: \paragraph{Deterministic and non-deterministic state machines}
fp@369: 
fp@369: A state machine can be deterministic, meaning that for one state and
fp@369: input, there is one (and only one) following state. In this case, the
fp@369: state machine has exactly one starting state. Non-deterministic state
fp@369: machines can have more than one transitions for a single state-input
fp@369: combination. There is a set of starting states in the latter case.
fp@369: 
fp@369: \paragraph{Moore and Mealy machines}
fp@369: 
fp@369: There is a distinction between so-called \textit{Moore machines}, and
fp@369: \textit{Mealy machines}. Mathematically spoken, the distinction lies
fp@369: in the output function $\omega$: If it only depends on the current
fp@369: state ($\omega: S \rightarrow \Gamma$), the machine corresponds to the
fp@369: ``Moore Model''. Otherwise, if $\omega$ is a function of a state and
fp@369: the input alphabet ($\omega: S \times \Sigma \rightarrow \Gamma$) the
fp@369: state machine corresponds to the ``Mealy model''. Mealy machines are
fp@369: the more practical solution in most cases, because their design allows
fp@369: machines with a minimum number of states. In practice, a mixture of
fp@369: both models is often used.
fp@369: 
fp@369: \paragraph{Misunderstandings about state machines}
fp@369: 
fp@369: There is a phenomenon called ``state explosion'', that is oftenly
fp@369: taken as a counter-argument against general use of state machines in
fp@369: complex environments. It has to be mentioned, that this point is
fp@369: misleading~\cite{fsmmis}. State explosions happen usually as a result
fp@369: of a bad state machine design: Common mistakes are storing the present
fp@369: values of all inputs in a state, or not dividing a complex state
fp@369: machine into simpler sub state machines. The EtherCAT master uses
fp@369: serveral state machines, that are executed hierarchically and so serve
fp@369: as sub state machines. These are also described below.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Master's State Model}
fp@369: \label{sec:statemodel}
fp@369: 
fp@369: This section will introduce the techniques used in the master to
fp@369: implement state machines.
fp@369: 
fp@369: \paragraph{State Machine Programming}
fp@369: 
fp@369: There are certain ways to implement a state machine in \textit{C}
fp@369: code. An obvious way is to implement the different states and actions
fp@369: by one big case differentiation:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   enum {STATE_1, STATE_2, STATE_3};
fp@369:   int state = STATE_1;
fp@369: 
fp@369:   void state_machine_run(void *priv_data) {
fp@369:           switch (state) {
fp@369:                   case STATE_1:
fp@369:                           action_1();
fp@369:                           state = STATE_2;
fp@369:                           break;
fp@369:                   case STATE_2:
fp@369:                           action_2()
fp@369:                           if (some_condition) state = STATE_1;
fp@369:                           else state = STATE_3;
fp@369:                           break;
fp@369:                   case STATE_3:
fp@369:                           action_3();
fp@369:                           state = STATE_1;
fp@369:                           break;
fp@369:           }
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: For small state machines, this is an option. The disadvantage is, that
fp@369: with an increasing number of states the code soon gets complex and an
fp@369: additional case differentiation is executed each run. Besides, lots of
fp@369: indentation is wasted.
fp@369: 
fp@369: The method used in the master is to implement every state in an own
fp@369: function and to store the current state function with a function
fp@369: pointer:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   void (*state)(void *) = state1;
fp@369: 
fp@369:   void state_machine_run(void *priv_data) {
fp@369:           state(priv_data);
fp@369:   }
fp@369: 
fp@369:   void state1(void *priv_data) {
fp@369:           action_1();
fp@369:           state = state2;
fp@369:   }
fp@369: 
fp@369:   void state2(void *priv_data) {
fp@369:           action_2();
fp@369:           if (some_condition) state = state1;
fp@369:           else state = state2;
fp@369:   }
fp@369: 
fp@369:   void state3(void *priv_data) {
fp@369:           action_3();
fp@369:           state = state1;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: In the master code, state pointers of all state machines\footnote{All
fp@369:   except for the EoE state machine, because multiple EoE slaves have
fp@369:   to be handled in parallel. For this reason each EoE handler object
fp@369:   has its own state pointer.} are gathered in a single object of the
fp@369: \textit{ec\_fsm\_t} class. This is advantageous, because there is
fp@369: always one instance of every state machine available and can be
fp@369: started on demand.
fp@369: 
fp@369: \paragraph{Mealy and Moore}
fp@369: 
fp@369: If a closer look is taken to the above listing, it can be seen that
fp@369: the actions executed (the ``outputs'' of the state machine) only
fp@369: depend on the current state. This accords to the ``Moore'' model
fp@369: introduced in section~\ref{sec:fsmtheory}. As mentioned, the ``Mealy''
fp@369: model offers a higher flexibility, which can be seen in the listing
fp@369: below:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   void state7(void *priv_data) {
fp@369:           if (some_condition) {
fp@369:                   action_7a();
fp@369:                   state = state1;
fp@369:           }
fp@369:           else {
fp@369:                   action_7b();
fp@369:                   state = state8;
fp@369:           }
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3} + \textcircled{\tiny 7}] The
fp@369:   state function executes the actions depending on the state
fp@369:   transition, that is about to be done.
fp@369: \end{description}
fp@369: 
fp@369: The most flexible alternative is to execute certain actions depending
fp@369: on the state, followed by some actions dependent on the state
fp@369: transition:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   void state9(void *priv_data) {
fp@369:           action_9();
fp@369:           if (some_condition) {
fp@369:                   action_9a();
fp@369:                   state = state7;
fp@369:           }
fp@369:           else {
fp@369:                   action_9b();
fp@369:                   state = state10;
fp@369:           }
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: This model is oftenly used in the master. It combines the best aspects
fp@369: of both approaches.
fp@369: 
fp@369: \paragraph{Using Sub State Machines}
fp@369: 
fp@369: To avoid having too much states, certain functions of the EtherCAT
fp@369: master state machine have been sourced out into sub state machines.
fp@369: This helps to encapsule the related workflows and moreover avoids the
fp@369: ``state explosion'' phenomenon described in
fp@369: section~\ref{sec:fsmtheory}. If the master would instead use one big
fp@369: state machine, the number of states would be a multiple of the actual
fp@369: number. This would increase the level of complexity to a
fp@369: non-manageable grade.
fp@369: 
fp@369: \paragraph{Executing Sub State Machines}
fp@369: 
fp@369: If a state machine starts to execute a sub state machine, it usually
fp@369: remains in one state until the sub state machine terminates. This is
fp@369: usually done like in the listing below, which is taken out of the
fp@369: slave configuration state machine code:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left]
fp@369:   void ec_fsm_slaveconf_saveop(ec_fsm_t *fsm)
fp@369:   {
fp@369:           fsm->change_state(fsm); // execute state change
fp@369:                                   // sub state machine
fp@369: 
fp@369:           if (fsm->change_state == ec_fsm_error) {
fp@369:                   fsm->slave_state = ec_fsm_end;
fp@369:                   return;
fp@369:           }
fp@369: 
fp@369:           if (fsm->change_state != ec_fsm_end) return;
fp@369: 
fp@369:           // continue state processing
fp@369:           ...
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] \textit{change\_state} is the
fp@369:   state pointer of the state change state machine. The state function,
fp@369:   the pointer points on, is executed\ldots
fp@369: \item[\normalfont\textcircled{\tiny 6}] \ldots either until the state
fp@369:   machine terminates with the error state \ldots
fp@369: \item[\normalfont\textcircled{\tiny 11}] \ldots or until the state
fp@369:   machine terminates in the end state. Until then, the ``higher''
fp@369:   state machine remains in the current state and executes the sub
fp@369:   state machine again in the next cycle.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{State Machine Descriptions}
fp@369: 
fp@369: The below sections describe every state machine used in the EtherCAT
fp@369: master. The textual descriptions of the state machines contain
fp@369: references to the transitions in the corresponding state transition
fp@369: diagrams, that are marked with an arrow followed by the name of the
fp@369: successive state.  Transitions caused by trivial error cases (i.~e. no
fp@369: response from slave) are not described explicitly. These transitions
fp@369: are drawn as dashed arrows in the diagrams.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Operation State Machine}
fp@369: \label{sec:fsm-op}
fp@369: \index{FSM!Operation}
fp@369: 
fp@369: The Operation state machine is executed by calling the
fp@369: \textit{ecrt\_master\_run()} method in cyclic realtime code. Its
fp@369: purpose is to monitor the bus and to reconfigure slaves after a bus
fp@369: failure or power failure. Figure~\ref{fig:fsm-op} shows its transition
fp@369: diagram.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.8\textwidth]{images/fsm-op}
fp@369:   \caption{Transition diagram of the operation state machine}
fp@369:   \label{fig:fsm-op}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[START] This is the beginning state of the operation state
fp@369:   machine. There is a datagram issued, that queries the ``AL Control
fp@369:   Response'' attribute \cite[section~5.3.2]{alspec} of all slaves via
fp@369:   broadcast. In this way, all slave states and the number of slaves
fp@369:   responding can be determined.  $\rightarrow$~\textit{BROADCAST}
fp@369: 
fp@369: \item[BROADCAST] The broadcast datagram is evaluated. A change in the
fp@369:   number of responding slaves is treates as a topology change. If the
fp@369:   number of slaves is not as expected, the bus is marked as
fp@369:   ``tainted''. In this state, no slave reconfiguration is possible,
fp@369:   because the assignment of known slaves and those present on the bus
fp@369:   is ambiguous. If the number of slaves is considered as right, the
fp@369:   bus is marked for validation, because it turned from tainted to
fp@369:   normal state and it has to be checked, if all slaves are valid. Now,
fp@369:   the state of every single slave has to be determined. For that, a
fp@369:   (unicast) datagram is issued, that queries the first slave's ``AL
fp@369:   Control Response'' attribute. $\rightarrow$~\textit{READ STATES}
fp@369: 
fp@369: \item[READ STATES] If the current slave did not respond to its
fp@369:   configured station address, it is marked as offline, and the next
fp@369:   slave is queried. $\rightarrow$~\textit{READ STATES}
fp@369: 
fp@369:   If the slave responded, it is marked as online and its current state
fp@369:   is stored. The next slave is queried. $\rightarrow$~\textit{READ
fp@369:     STATES}
fp@369: 
fp@369:   If all slaves have been queried, and the bus is marked for
fp@369:   validation, the validation is started by checking the first slaves
fp@369:   vendor ID. $\rightarrow$~\textit{VALIDATE VENDOR}
fp@369: 
fp@369:   If no validation has to be done, it is checked, if all slaves are in
fp@369:   the state they are supposed to be. If not, the first of slave with
fp@369:   the wrong state is reconfigured and brought in the required state.
fp@369:   $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   If all slaves are in the correct state, the state machine is
fp@369:   restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369: \item[CONFIGURE SLAVES] The slave configuration state machine is
fp@369:   executed until termination. $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   If there are still slaves in the wrong state after another check,
fp@369:   the first of these slaves is configured and brought into the correct
fp@369:   state again. $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   If all slaves are in the correct state, the state machine is
fp@369:   restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369: \item[VALIDATE VENDOR] The SII state machine is executed until
fp@369:   termination. If the slave has the wrong vendor ID, the state machine
fp@369:   is restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369:   If the slave has the correct vendor ID, its product ID is queried.
fp@369:   $\rightarrow$~\textit{VALIDATE PRODUCT}
fp@369: 
fp@369: \item[VALIDATE PRODUCT] The SII state machine is executed until
fp@369:   termination. If the slave has the wrong product ID, the state
fp@369:   machine is restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369:   If the slave has the correct product ID, the next slave's vendor ID
fp@369:   is queried. $\rightarrow$~\textit{VALIDATE VENDOR}
fp@369: 
fp@369:   If all slaves have the correct vendor IDs and product codes, the
fp@369:   configured station addresses can be safely rewritten. This is done
fp@369:   for the first slave marked as offline.
fp@369:   $\rightarrow$~\textit{REWRITE ADDRESSES}
fp@369: 
fp@369: \item[REWRITE ADDRESSES] If the station address was successfully
fp@369:   written, it is sear\-ched for the next slave marked as offline. If
fp@369:   there is one, its address is reconfigured, too.
fp@369:   $\rightarrow$~\textit{REWRITE ADDRESSES}
fp@369: 
fp@369:   If there are no more slaves marked as offline, the state machine is
fp@369:   restarted. $\rightarrow$~\textit{START}
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Idle State Machine}
fp@369: \label{sec:fsm-idle}
fp@369: \index{FSM!Idle}
fp@369: 
fp@369: The Idle state machine is executed by a kernel workqueue, if no
fp@369: realtime module is connected. Its purpose is to make slave information
fp@369: available to user space, operate EoE-capable slaves, read and write
fp@369: E$^2$PROM contents and test slave functionality.
fp@369: Figure~\ref{fig:fsm-idle} shows its transition diagram.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.8\textwidth]{images/fsm-idle}
fp@369:   \caption{Transition diagram of the idle state machine}
fp@369:   \label{fig:fsm-idle}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[START] The beginning state of the idle state machine. Similar to
fp@369:   the operation state machine, a broadcast datagram is issued, to
fp@369:   query all slave states and the number of slaves.
fp@369:   $\rightarrow$~\textit{BROADCAST}
fp@369: 
fp@369: \item[BROADCAST] The number of responding slaves is evaluated. If it
fp@369:   has changed since the last time, this is treated as a topology
fp@369:   change and the internal list of slaves is cleared and rebuild
fp@369:   completely. The slave scan state machine is started for the first
fp@369:   slave. $\rightarrow$~\textit{SCAN FOR SLAVES}
fp@369: 
fp@369:   If no topology change happened, every single slave state is fetched.
fp@369:   $\rightarrow$~\textit{READ STATES}
fp@369: 
fp@369: \item[SCAN FOR SLAVES] The slave scan state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{SCAN FOR SLAVES}
fp@369: 
fp@369:   If there is another slave to scan, the slave scan state machine is
fp@369:   started again. $\rightarrow$~\textit{SCAN FOR SLAVES}
fp@369: 
fp@369:   If all slave information has been fetched, slave addresses are
fp@369:   calculated and EoE processing is started. Then, the state machine is
fp@369:   restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369: \item[READ STATES] If the slave did not respond to the query, it is
fp@369:   marked as offline. The next slave is queried.
fp@369:   $\rightarrow$~\textit{READ STATES}
fp@369: 
fp@369:   If the slave responded, it is marked as online. And the next slave
fp@369:   is queried. $\rightarrow$~\textit{READ STATES}
fp@369: 
fp@369:   If all slave states have been determined, it is checked, if any
fp@369:   slaves are not in the state they supposed to be. If this is true,
fp@369:   the slave configuration state machine is started for the first of
fp@369:   them. $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   If all slaves are in the correct state, it is checked, if any
fp@369:   E$^2$PROM write operations are pending. If this is true, the first
fp@369:   pending operation is executed by starting the SII state machine for
fp@369:   writing access. $\rightarrow$~\textit{WRITE EEPROM}
fp@369: 
fp@369:   If all these conditions are false, there is nothing to do and the
fp@369:   state machine is restarted. $\rightarrow$~\textit{START}
fp@369: 
fp@369: \item[CONFIGURE SLAVES] The slave configuration state machine is
fp@369:   executed until termination. $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   After this, it is checked, if another slave needs a state change. If
fp@369:   this is true, the slave state change state machine is started for
fp@369:   this slave. $\rightarrow$~\textit{CONFIGURE SLAVES}
fp@369: 
fp@369:   If all slaves are in the correct state, it is determined, if any
fp@369:   E$^2$PROM write operations are pending. If this is true, the first
fp@369:   pending operation is executed by starting the SII state machine for
fp@369:   writing access. $\rightarrow$~\textit{WRITE EEPROM}
fp@369: 
fp@369:   If all prior conditions are false, the state machine is restarted.
fp@369:   $\rightarrow$~\textit{START}
fp@369: 
fp@369: \item[WRITE EEPROM] The SII state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{WRITE EEPROM}
fp@369: 
fp@369:   If the current word has been written successfully, and there are
fp@369:   still word to write, the SII state machine is started for the next
fp@369:   word. $\rightarrow$~\textit{WRITE EEPROM}
fp@369: 
fp@369:   If all words have been written successfully, the new E$^2$PROM
fp@369:   contents are evaluated and the state machine is restarted.
fp@369:   $\rightarrow$~\textit{START}
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Slave Scan State Machine}
fp@369: \label{sec:fsm-scan}
fp@369: \index{FSM!Slave Scan}
fp@369: 
fp@369: The slave scan state machine, which can be seen in
fp@369: figure~\ref{fig:fsm-slavescan}, leads through the process of fetching
fp@369: all slave information.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.6\textwidth]{images/fsm-slavescan}
fp@369:   \caption{Transition diagram of the slave scan state machine}
fp@369:   \label{fig:fsm-slavescan}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[START] In the beginning state of the slave scan state machine,
fp@369:   the station address is written to the slave, which is always the
fp@369:   ring position~+~$1$. In this way, the address 0x0000 (default
fp@369:   address) is not used, which makes it easy to detect unconfigured
fp@369:   slaves.  $\rightarrow$~\textit{ADDRESS}
fp@369: 
fp@369: \item[ADDRESS] The writing of the station address is verified. After
fp@369:   that, the slave's ``AL Control Response'' attribute is queried.
fp@369:   $\rightarrow$~\textit{STATE}
fp@369: 
fp@369: \item[STATE] The AL state is evaluated. A warning is output, if the
fp@369:   slave has still the \textit{Change} bit set. After that, the slave's
fp@369:   ``DL Information'' attribute is queried.
fp@369:   $\rightarrow$~\textit{BASE}
fp@369: 
fp@369: \item[BASE] The queried base data are evaluated: Slave type, revision
fp@369:   and build number, and even more important, the number of supported
fp@369:   sync managers and FMMUs are stored. After that, the slave's data
fp@369:   link layer information is read from the ``DL Status'' attribute at
fp@369:   address 0x0110. $\rightarrow$~\textit{DATALINK}
fp@369: 
fp@369: \item[DATALINK] In this state, the DL information is evaluated: This
fp@369:   information about the communication ports contains, if the link is
fp@369:   up, if the loop has been closed and if there is a carrier detected
fp@369:   on the RX side of each port.
fp@369: 
fp@369:   Then, the state machine starts measuring the size of the slave's
fp@369:   E$^2$PROM contents. This is done by subsequently reading out each
fp@369:   category header, until the last category is reached (type 0xFFFF).
fp@369:   This procedure is started by querying the first category header at
fp@369:   word address 0x0040 via the SII state machine.
fp@369:   $\rightarrow$~\textit{EEPROM SIZE}
fp@369: 
fp@369: \item[EEPROM SIZE] The SII state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{EEPROM SIZE}
fp@369: 
fp@369:   If the category type does not mark the end of the categories, the
fp@369:   position of the next category header is determined via the length of
fp@369:   the current category, and the SII state machine is started again.
fp@369:   $\rightarrow$~\textit{EEPROM SIZE}
fp@369: 
fp@369:   If the size of the E$^2$PROM contents has been determined, memory is
fp@369:   allocated, to read all the contents. The SII state machine is
fp@369:   started to read the first word. $\rightarrow$~\textit{EEPROM DATA}
fp@369: 
fp@369: \item[EEPROM DATA] The SII state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{EEPROM DATA}
fp@369: 
fp@369:   Two words have been read. If more than one word is needed, the two
fp@369:   words are written in the allocated memory. Otherwise only one word
fp@369:   (the last word) is copied. If more words are to read, the SII state
fp@369:   machine is started again to read the next two words.
fp@369:   $\rightarrow$~\textit{EEPROM DATA}
fp@369: 
fp@369:   The complete E$^2$PROM contents have been read. The slave's identity
fp@369:   object and mailbox information are evaluated. Moreover the category
fp@369:   types STRINGS, GENERAL, SYNC and PDO are evaluated. The slave
fp@369:   scanning has been completed. $\rightarrow$~\textit{END}
fp@369: 
fp@369: \item[END] Slave scanning has been finished.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Slave Configuration State Machine}
fp@369: \label{sec:fsm-conf}
fp@369: \index{FSM!Slave Configuration}
fp@369: 
fp@369: The slave configuration state machine, which can be seen in
fp@369: figure~\ref{fig:fsm-slaveconf}, leads through the process of
fp@369: configuring a slave and bringing it to a certain state.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.6\textwidth]{images/fsm-slaveconf}
fp@369:   \caption{Transition diagram of the slave configuration state
fp@369:     machine}
fp@369:   \label{fig:fsm-slaveconf}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[INIT] The state change state machine has been initialized to
fp@369:   bring the slave into the \textit{INIT} state. Now, the slave state
fp@369:   change state machine is executed until termination.
fp@369:   $\rightarrow$~\textit{INIT}
fp@369: 
fp@369:   If the slave state change failed, the configuration has to be
fp@369:   aborted. $\rightarrow$~\textit{END}
fp@369: 
fp@369:   The slave state change succeeded and the slave is now in
fp@369:   \textit{INIT} state. If this is the target state, the configuration
fp@369:   is finished. $\rightarrow$~\textit{END}
fp@369: 
fp@369:   If the slave does not support any sync managers, the sync manager
fp@369:   configuration can be skipped. The state change state machine is
fp@369:   started to bring the slave into \textit{PREOP} state.
fp@369:   $\rightarrow$~\textit{PREOP}
fp@369: 
fp@369:   Sync managers are configured conforming to the sync manager category
fp@369:   information provided in the slave's E$^2$PROM. The corresponding
fp@369:   datagram is issued. $\rightarrow$~\textit{SYNC}
fp@369: 
fp@369: \item[SYNC] If the sync manager configuration datagram is accepted,
fp@369:   the sync manager configuration was successful. The slave may now
fp@369:   enter the \textit{PREOP} state, and the state change state machine
fp@369:   is started. $\rightarrow$~\textit{PREOP}
fp@369: 
fp@369: \item[PREOP] The state change state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{PREOP}
fp@369: 
fp@369:   If the state change failed, the configuration has to be aborted.
fp@369:   $\rightarrow$~\textit{END}
fp@369: 
fp@369:   If the \textit{PREOP} state was the target state, the configuration
fp@369:   is finished. $\rightarrow$~\textit{END}
fp@369: 
fp@369:   If the slave supports no FMMUs, the FMMU configuration can be
fp@369:   skipped. If the slave has SDOs to configure, it is begun with
fp@369:   sending the first SDO. $\rightarrow$~\textit{SDO\_CONF}
fp@369: 
fp@369:   If no SDO configurations are provided, the slave can now directly be
fp@369:   brought into the \textit{SAVEOP} state and the state change state
fp@369:   machine is started again. $\rightarrow$~\textit{SAVEOP}
fp@369: 
fp@369:   Otherwise, all supported FMMUs are configured according to the PDOs
fp@369:   requested via the master's realtime interface. The appropriate
fp@369:   datagram is issued. $\rightarrow$~\textit{FMMU}
fp@369: 
fp@369: \item[FMMU] The FMMU configuration datagram was accepted. If the slave
fp@369:   has SDOs to configure, it is begun with sending the first SDO.
fp@369:   $\rightarrow$~\textit{SDO\_CONF}
fp@369: 
fp@369:   Otherwise, the slave can now be brought into the \textit{SAVEOP}
fp@369:   state. The state change state machine is started.
fp@369:   $\rightarrow$~\textit{SAVEOP}
fp@369: 
fp@369: \item[SDO\_CONF] The CoE state machine is executed until termination.
fp@369:   $\rightarrow$~\textit{SDO\_CONF}
fp@369: 
fp@369:   If another SDO has to be configured, a new SDO download sequence is
fp@369:   begun. $\rightarrow$~\textit{SDO\_CONF}
fp@369: 
fp@369:   Otherwise, the slave can now be brought into the \textit{SAVEOP}
fp@369:   state. The state change state machine is started.
fp@369:   $\rightarrow$~\textit{SAVEOP}
fp@369: 
fp@369: \item[SAVEOP] The state change state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{SAVEOP}
fp@369: 
fp@369:   If the state change failed, the configuration has to be aborted.
fp@369:   $\rightarrow$~\textit{END}
fp@369: 
fp@369:   If the \textit{SAVEOP} state was the target state, the configuration
fp@369:   is finished. $\rightarrow$~\textit{END}
fp@369: 
fp@369:   The slave can now directly be brought into the \textit{OP} state and
fp@369:   the state change state machine is started a last time.
fp@369:   $\rightarrow$~\textit{OP}
fp@369: 
fp@369: \item[OP] The state change state machine is executed until
fp@369:   termination. $\rightarrow$~\textit{OP}
fp@369: 
fp@369:   If the state change state machine terminates, the slave
fp@369:   configuration is finished, regardless of its success.
fp@369:   $\rightarrow$~\textit{END}
fp@369: 
fp@369: \item[END] The termination state.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The State Change State Machine}
fp@369: \label{sec:fsm-change}
fp@369: \index{FSM!State Change}
fp@369: 
fp@369: The state change state machine, which can be seen in
fp@369: figure~\ref{fig:fsm-change}, leads through the process of changing a
fp@369: slave's state. This implements the states and transitions described in
fp@369: \cite[section~6.4.1]{alspec}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/fsm-change}
fp@369:   \caption{Transition diagram of the state change state machine}
fp@369:   \label{fig:fsm-change}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[START] The beginning state, where a datagram with the state
fp@369:   change command is written to the slave's ``AL Control Request''
fp@369:   attribute. Nothing can fail. $\rightarrow$~\textit{CHECK}
fp@369: 
fp@369: \item[CHECK] After the state change datagram has been sent, the ``AL
fp@369:   Control Response'' attribute is queried with a second datagram.
fp@369:   $\rightarrow$~\textit{STATUS}
fp@369: 
fp@369: \item[STATUS] The read memory contents are evaluated: While the
fp@369:   parameter \textit{State} still contains the old slave state, the
fp@369:   slave is busy with reacting on the state change command. In this
fp@369:   case, the attribute has to be queried again.
fp@369:   $\rightarrow$~\textit{STATUS}
fp@369: 
fp@369:   In case of success, the \textit{State} parameter contains the new
fp@369:   state and the \textit{Change} bit is cleared. The slave is in the
fp@369:   requested state.  $\rightarrow$~\textit{END}
fp@369: 
fp@369:   If the slave can not process the state change, the \textit{Change}
fp@369:   bit is set: Now the master tries to get the reason for this by
fp@369:   querying the \textit{AL Status Code} parameter.
fp@369:   $\rightarrow$~\textit{CODE}
fp@369: 
fp@369: \item[END] If the state machine ends in this state, the slaves's state
fp@369:   change has been successful.
fp@369: 
fp@369: \item[CODE] The status code query has been sent. Reading the
fp@369:   \textit{AL Status Code} might fail, because not all slaves support
fp@369:   this parameter. Anyway, the master has to acknowledge the state
fp@369:   change error by writing the current slave state to the ``AL Control
fp@369:   Request'' attribute with the \textit{Acknowledge} bit set.
fp@369:   $\rightarrow$~\textit{ACK}
fp@369: 
fp@369: \item[ACK] After that, the ``AL Control Response'' attribute is
fp@369:   queried for the state of the acknowledgement.
fp@369:   $\rightarrow$~\textit{CHECK ACK}
fp@369: 
fp@369: \item[CHECK ACK] If the acknowledgement has been accepted by the
fp@369:   slave, the old state is kept. Still, the state change was
fp@369:   unsuccessful. $\rightarrow$~\textit{ERROR}
fp@369: 
fp@369:   If the acknowledgement is ignored by the slave, a timeout happens.
fp@369:   In any case, the overall state change was unsuccessful.
fp@369:   $\rightarrow$~\textit{ERROR}
fp@369: 
fp@369:   If there is still now response from the slave, but the timer did not
fp@369:   run out yet, the slave's ``AL Control Response'' attribute is
fp@369:   queried again.  $\rightarrow$~\textit{CHECK ACK}
fp@369: 
fp@369: \item[ERROR] If the state machine ends in this state, the slave's
fp@369:   state change was unsuccessful.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The SII State Machine}
fp@369: \label{sec:fsm-sii}
fp@369: \index{FSM!SII}
fp@369: 
fp@369: The SII\index{SII} state machine (shown in figure~\ref{fig:fsm-sii})
fp@369: implements the process of reading or writing E$^2$PROM data via the
fp@369: Slave Information Interface described in \cite[section~5.4]{alspec}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/fsm-sii}
fp@369:   \caption{Transition diagram of the SII state machine}
fp@369:   \label{fig:fsm-sii}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[READ\_START] The beginning state for reading access, where the
fp@369:   read request and the requested address are written to the SII
fp@369:   attribute. Nothing can fail up to now.
fp@369:   $\rightarrow$~\textit{READ\_CHECK}
fp@369: 
fp@369: \item[READ\_CHECK] When the SII read request has been sent
fp@369:   successfully, a timer is started. A check/fetch datagram is issued,
fp@369:   that reads out the SII attribute for state and data.
fp@369:   $\rightarrow$~\textit{READ\_FETCH}
fp@369: 
fp@369: \item[READ\_FETCH] Upon reception of the check/fetch datagram, the
fp@369:   \textit{Read Operation} and \textit{Busy} parameters are checked:
fp@369:   \begin{itemize}
fp@369:   \item If the slave is still busy with fetching E$^2$PROM data into
fp@369:     the interface, the timer is checked. If it timed out, the reading
fp@369:     is aborted ($\rightarrow$~\textit{ERROR}), if not, the check/fetch
fp@369:     datagram is issued again. $\rightarrow$~\textit{READ\_FETCH}
fp@369: 
fp@369:   \item If the slave is ready with reading data, these are copied from
fp@369:     the datagram and the read cycle is completed.
fp@369:     $\rightarrow$~\textit{END}
fp@369:   \end{itemize}
fp@369: \end{description}
fp@369: 
fp@369: The write access states behave nearly the same:
fp@369: 
fp@369: \begin{description}
fp@369: \item[WRITE\_START] The beginning state for writing access,
fp@369:   respectively. A write request, the target address and the data word
fp@369:   are written to the SII attribute. Nothing can fail.
fp@369:   $\rightarrow$~\textit{WRITE\_CHECK}
fp@369: 
fp@369: \item[WRITE\_CHECK] When the SII write request has been sent
fp@369:   successfully, the timer is started. A check datagram is issued, that
fp@369:   reads out the SII attribute for the state of the write operation.
fp@369:   $\rightarrow$~\textit{WRITE\_CHECK2}
fp@369: 
fp@369: \item[WRITE\_CHECK2] Upon reception of the check datagram, the
fp@369:   \textit{Write Operation} and \textit{Busy} parameters are checked:
fp@369:   \begin{itemize}
fp@369:   \item If the slave is still busy with writing E$^2$PROM data, the
fp@369:     timer is checked. If it timed out, the operation is aborted
fp@369:     ($\rightarrow$~\textit{ERROR}), if not, the check datagram is
fp@369:     issued again. $\rightarrow$~\textit{WRITE\_CHECK2}
fp@369:   \item If the slave is ready with writing data, the write cycle is
fp@369:     completed. $\rightarrow$~\textit{END}
fp@369:   \end{itemize}
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Mailbox Protocol Implementations}
fp@369: \index{Mailbox}
fp@369: 
fp@369: The EtherCAT master implements the EoE and the CoE mailbox
fp@369: protocols. See the below section for details.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Ethernet-over-EtherCAT (EoE)}
fp@369: \label{sec:eoeimp}
fp@369: \index{EoE}
fp@369: 
fp@369: The EtherCAT master implements the Ethernet-over-EtherCAT mailbox
fp@369: protocol to enable the tunneling of Ethernet frames to special slaves,
fp@369: that can either have physical Ethernet ports to forward the frames to,
fp@369: or have an own IP stack to receive the frames.
fp@369: 
fp@369: \paragraph{Virtual Network Interfaces}
fp@369: 
fp@369: The master creates a virtual EoE network interface for every
fp@369: EoE-capable slave. These interfaces are called \textit{eoeX}, where X
fp@369: is a number provided by the kernel on interface registration. Frames
fp@369: sent to these interfaces are forwarded to the associated slaves by the
fp@369: master. Frames, that are received by the slaves, are fetched by the
fp@369: master and forwarded to the virtual interfaces.
fp@369: 
fp@369: This bears the following advantages:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item Flexibility: The user can decide, how the EoE-capable slaves are
fp@369:   interconnected with the rest of the world.
fp@369: \item Standard tools can be used to monitor the EoE activity and to
fp@369:   configure the EoE interfaces.
fp@369: \item The Linux kernel's layer-2-bridging implementation (according to
fp@369:   the IEEE 802.1D MAC Bridging standard) can be used natively to
fp@369:   bridge Ethernet traffic between EoE-capable slaves.
fp@369: \item The Linux kernel's network stack can be used to route packets
fp@369:   between EoE-capable slaves and to track security issues, just like
fp@369:   having physical network interfaces.
fp@369: \end{itemize}
fp@369: 
fp@369: \paragraph{EoE Handlers}
fp@369: 
fp@369: The virtual EoE interfaces and the related functionality is encapsuled
fp@369: in the \textit{ec\_eoe\_t} class (see section~\ref{sec:class-eoe}).
fp@369: So the master does not create the network interfaces directly: This is
fp@369: done inside the constructor of the \textit{ec\_eoe\_t} class. An
fp@369: object of this class is called ``EoE handler'' below. An EoE handler
fp@369: additionaly contains a frame queue. Each time, the kernel passes a new
fp@369: socket buffer for sending via the interface's
fp@369: \textit{hard\_start\_xmit()} callback, the socket buffer is queued for
fp@369: transmittion by the EoE state machine (see below). If the queue gets
fp@369: filled up, the passing of new socket buffers is suspended with a call
fp@369: to \textit{netif\_stop\_queue()}.
fp@369: 
fp@369: \paragraph{Static Handler Creation}
fp@369: 
fp@369: The master creates a pool of EoE handlers at startup, that are coupled
fp@369: to EoE-capable slaves on demand. The lifetime of the corresponding
fp@369: network interfaces is equal to the lifetime of the master module.
fp@369: This approach is opposed to creating the virtual network interfaces on
fp@369: demand (i.~e. on running across a new EoE-capable slave). The latter
fp@369: approach was considered as difficult, because of serveral reasons:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item The \textit{alloc\_netdev()} function can sleep and must be
fp@369:   called from a non-interrupt context. This reduces the flexibility of
fp@369:   choosing an appropriate method for cyclic EoE processing.
fp@369: \item Unregistering network interfaces requires them to be ``down'',
fp@369:   which can not be guaranteed upon sudden disappearing of an
fp@369:   EoE-capable slave.
fp@369: \item The connection to the EoE-capable slaves must be as continuous
fp@369:   as possible. Especially the transition from idle to operation mode
fp@369:   (and vice versa) causes the rebuilding of the internal data
fp@369:   structures. These transitions must be as transparent as possible for
fp@369:   the instances using the network interfaces.
fp@369: \end{itemize}
fp@369: 
fp@369: \paragraph{Number of Handlers}
fp@369: 
fp@369: The master module has a parameter \textit{ec\_eoeif\_count} to specify
fp@369: the number of EoE interfaces (and handlers) per master to create. This
fp@369: parameter can either be specified when manually loading the master
fp@369: module, or (when using the init script) by setting the
fp@374: \textit{EOE\_INTERFACES} variable in the sysconfig file (see
fp@369: section~\ref{sec:sysconfig}). Upon loading of the master module, the
fp@369: virtual interfaces become available:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{ifconfig -a}`
fp@369:   eoe0      Link encap:Ethernet  HWaddr 00:11:22:33:44:06
fp@369:             BROADCAST MULTICAST  MTU:1500  Metric:1
fp@369:             RX packets:0 errors:0 dropped:0 overruns:0 frame:0
fp@369:             TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
fp@369:             collisions:0 txqueuelen:1000
fp@369:             RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
fp@369: 
fp@369:   eoe1      Link encap:Ethernet  HWaddr 00:11:22:33:44:07
fp@369:             BROADCAST MULTICAST  MTU:1500  Metric:1
fp@369:             RX packets:0 errors:0 dropped:0 overruns:0 frame:0
fp@369:             TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
fp@369:             collisions:0 txqueuelen:1000
fp@369:             RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
fp@369:   ...
fp@369: \end{lstlisting}
fp@369: 
fp@369: \paragraph{Coupling of EoE Slaves}
fp@369: 
fp@369: During execution of the slave scan state machine (see
fp@369: section~\ref{sec:fsm-scan}), the master determines the supported
fp@369: mailbox protocols. This is done by examining the ``Supported Mailbox
fp@369: Protocols'' mask field at word address 0x001C of the SII\index{SII}.
fp@369: If bit 1 is set, the slave supports the EoE protocol. After slave
fp@369: scanning, the master runs through all slaves again and couples each
fp@369: EoE-capable slave to a free EoE handler. It can happen, that there are
fp@369: not enough EoE handlers to cover all EoE-capable slaves. In this case,
fp@369: the number of EoE handlers must be increased accordingly.
fp@369: 
fp@369: \paragraph{EoE State Machine}
fp@369: \index{FSM!EoE}
fp@369: 
fp@369: Every EoE handler owns an EoE state machine, that is used to send
fp@369: frames to the coupled slave and receive frames from the it via the EoE
fp@369: communication primitives. This state machine is showed in
fp@369: figure~\ref{fig:fsm-eoe}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.7\textwidth]{images/fsm-eoe}
fp@369:   \caption{Transition diagram of the EoE state machine}
fp@369:   \label{fig:fsm-eoe}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[RX\_START] The beginning state of the EoE state machine. A
fp@369:   mailbox check datagram is sent, to query the slave's mailbox for new
fp@369:   frames. $\rightarrow$~\textit{RX\_CHECK}
fp@369: 
fp@369: \item[RX\_CHECK] The mailbox check datagram is received. If the
fp@369:   slave's mailbox did not contain data, a transmit cycle is started.
fp@369:   $\rightarrow$~\textit{TX\_START}
fp@369: 
fp@369:   If there are new data in the mailbox, a datagram is sent to fetch
fp@369:   the new data. $\rightarrow$~\textit{RX\_FETCH}
fp@369: 
fp@369: \item[RX\_FETCH] The fetch datagram is received. If the mailbox data
fp@369:   do not contain a ``EoE Fragment request'' command, the data are
fp@369:   dropped and a transmit sequence is started.
fp@369:   $\rightarrow$~\textit{TX\_START}
fp@369: 
fp@369:   If the received Ethernet frame fragment is the first fragment, a new
fp@369:   socket buffer is allocated. In either case, the data are copied into
fp@369:   the correct position of the socket buffer.
fp@369: 
fp@369:   If the fragment is the last fragment, the socket buffer is forwarded
fp@369:   to the network stack and a transmit sequence is started.
fp@369:   $\rightarrow$~\textit{TX\_START}
fp@369: 
fp@369:   Otherwise, a new receive sequence is started to fetch the next
fp@369:   fragment. $\rightarrow$~\textit{RX\_\-START}
fp@369: 
fp@369: \item[TX\_START] The beginning state of a transmit sequence. It is
fp@369:   checked, if the transmittion queue contains a frame to send. If not,
fp@369:   a receive sequence is started. $\rightarrow$~\textit{RX\_START}
fp@369: 
fp@369:   If there is a frame to send, it is dequeued. If the queue was
fp@369:   inactive before (because it was full), the queue is woken up with a
fp@369:   call to \textit{netif\_wake\_queue()}. The first fragment of the
fp@369:   frame is sent. $\rightarrow$~\textit{TX\_SENT}
fp@369: 
fp@369: \item[TX\_SENT] It is checked, if the first fragment was sent
fp@369:   successfully. If the current frame consists of further fragments,
fp@369:   the next one is sent. $\rightarrow$~\textit{TX\_SENT}
fp@369: 
fp@369:   If the last fragment was sent, a new receive sequence is started.
fp@369:   $\rightarrow$~\textit{RX\_START}
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{EoE Processing}
fp@369: 
fp@369: To execute the EoE state machine of every active EoE handler, there
fp@369: must be a cyclic process. The easiest thing would be to execute the
fp@369: EoE state machines synchronously to the operation state machine (see
fp@369: section~\ref{sec:fsm-op}) with every realtime cycle. This approach has
fp@369: the following disadvantages:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item Only one EoE fragment can be sent or received every few cycles.
fp@369:   This causes the data rate to be very low, because the EoE state
fp@369:   machines are not executed in the time between the realtime
fp@369:   cycles. Moreover, the data rate would be dependent on the frequency
fp@369:   of the realtime process.
fp@369: \item The receiving and forwarding of frames to the kernel requires
fp@369:   the dynamic allocation of frames. Some realtime extensions do not
fp@369:   support calling memory allocation functions in realtime context, so
fp@369:   the EoE state machine may not be executed with each realtime cycle.
fp@369: \end{itemize}
fp@369: 
fp@369: To overcome these problems, an own cyclic process is needed to
fp@369: asynchronously execute the EoE state machines. For that, the master
fp@369: owns a kernel timer, that is executed each timer interrupt. This
fp@369: guarantees a constant bandwidth, but poses the new problem of
fp@369: concurrent access to the master. The locking mechanisms needed for
fp@369: this are introduced in section~\ref{sec:concurr}.
fp@369: Section~\ref{sec:concurrency} gives practical implementation examples.
fp@369: 
fp@369: \paragraph{Idle Mode}
fp@369: 
fp@369: EoE data must also be exchanged idle mode, to guarantee the continuous
fp@369: availability of the connection to the EoE-capable slaves. Although
fp@369: there is no realtime module connected in this case, the master is
fp@369: still accessed by the idle state machine (see
fp@369: section~\ref{sec:fsm-idle}), that is executed by the master's
fp@369: workqueue. With the EoE timer running in addition, there is still
fp@369: concurrency, that has to be protected by a lock. Therefore the master
fp@369: owns an internal spinlock that is used protect master access during
fp@369: idle mode.
fp@369: 
fp@369: \paragraph{Automatic Configuration}
fp@369: 
fp@369: By default, slaves are left in \textit{INIT} state during idle mode.
fp@369: If an EoE interface is set to running state (i.~e. with the
fp@369: \textit{ifconfig up} command), the requested slave state of the
fp@369: related slave is automatically set to \textit{OP}, whereupon the idle
fp@369: state machine will attempt to configure the slave and put it into
fp@369: operation.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{CANopen-over-EtherCAT (CoE)}
fp@369: \label{sec:coeimp}
fp@369: \index{CoE}
fp@369: 
fp@369: The CANopen-over-EtherCAT protocol \cite[section~5.6]{alspec} is used
fp@369: to configure slaves on application level. Each CoE-capable slave
fp@369: provides a list of SDOs for this reason.
fp@369: 
fp@369: \paragraph{SDO Configuration}
fp@369: 
fp@369: The SDO configurations have to be provided by the realtime module.
fp@369: This is done via the \textit{ecrt\_slave\_conf\_sdo*()} methods (see
fp@369: section~\ref{sec:ecrt-slave}), that are part of the realtime
fp@369: interface. The slave stores the SDO configurations in a linked list,
fp@369: but does not apply them at once.
fp@369: 
fp@369: \paragraph{SDO Download State Machine}
fp@369: 
fp@369: The best time to apply SDO configurations is during the slave's
fp@369: \textit{PREOP} state, because mailbox communication is already
fp@369: possible and slave's application will start with updating input data
fp@369: in the succeeding \textit{SAVEOP} state. Therefore the SDO
fp@369: configuration has to be part of the slave configuration state machine
fp@369: (see section~\ref{sec:fsm-conf}): It is implemented via an SDO
fp@369: download state machine, that is executed just before entering the
fp@369: slave's \textit{SAVEOP} state. In this way, it is guaranteed that the
fp@369: SDO configurations are applied each time, the slave is reconfigured.
fp@369: 
fp@369: The transition diagram of the SDO Download state machine can be seen
fp@369: in figure~\ref{fig:fsm-coedown}.
fp@369: 
fp@369: \begin{figure}[htbp]
fp@369:   \centering
fp@369:   \includegraphics[width=.9\textwidth]{images/fsm-coedown}
fp@369:   \caption{Transition diagram of the CoE download state machine}
fp@369:   \label{fig:fsm-coedown}
fp@369: \end{figure}
fp@369: 
fp@369: \begin{description}
fp@369: \item[START] The beginning state of the CoE download state
fp@369:   machine. The ``SDO Download Normal Request'' mailbox command is
fp@369:   sent. $\rightarrow$~\textit{REQUEST}
fp@369: 
fp@369: \item[REQUEST] It is checked, if the CoE download request has been
fp@369:   received by the slave. After that, a mailbox check command is issued
fp@369:   and a timer is started. $\rightarrow$~\textit{CHECK}
fp@369: 
fp@369: \item[CHECK] If no mailbox data is available, the timer is checked.
fp@369:   \begin{itemize}
fp@369:   \item If it timed out, the SDO download is aborted.
fp@369:     $\rightarrow$~\textit{ERROR}
fp@369:   \item Otherwise, the mailbox is queried again.
fp@369:     $\rightarrow$~\textit{CHECK}
fp@369:   \end{itemize}
fp@369: 
fp@369:   If the mailbox contains new data, the response is fetched.
fp@369:   $\rightarrow$~\textit{RESPONSE}
fp@369: 
fp@369: \item[RESPONSE] If the mailbox response could not be fetched, the data
fp@369:   is invalid, the wrong protocol was received, or a ``Abort SDO
fp@369:   Transfer Request'' was received, the SDO download is aborted.
fp@369:   $\rightarrow$~\textit{ERROR}
fp@369: 
fp@369:   If a ``SDO Download Normal Response'' acknowledgement was received,
fp@369:   the SDO download was successful. $\rightarrow$~\textit{END}
fp@369: 
fp@369: \item[END] The SDO download was successful.
fp@369: 
fp@369: \item[ERROR] The SDO download was aborted due to an error.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{User Space}
fp@369: \label{sec:user}
fp@369: \index{User space}
fp@369: 
fp@369: For the master runs as a kernel module, accessing it is natively
fp@369: limited to analyzing syslog messages and controlling using modutils.
fp@369: 
fp@369: It is necessary to implement further interfaces, that make it easier
fp@369: to access the master from user space and allow a finer influence. It
fp@369: should be possible to view and to change special parameters at runtime.
fp@369: 
fp@369: Bus visualization is a second point: For development and debugging
fp@369: purposes it would be nice, if one could show the connected slaves with
fp@369: a single command.
fp@369: 
fp@369: Another aspect is automatic startup and configuration. If the master
fp@369: is to be integrated into a running system, it must be able to
fp@369: automatically start with a persistent configuration.
fp@369: 
fp@369: A last thing is monitoring EtherCAT communication. For debugging
fp@369: purposes, there had to be a way to analyze EtherCAT datagrams. The
fp@369: best way would be with a popular network analyzer, like Wireshark
fp@369: \cite{wireshark} (the former Ethereal) or others.
fp@369: 
fp@369: This section covers all those points and introduces the interfaces and
fp@369: tools to make all that possible.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{The Sysfs Interface}
fp@369: \label{sec:sysfs}
fp@369: 
fp@369: The system filesystem (Sysfs\index{Sysfs}) was introduced with Linux
fp@369: kernel 2.5 and is a well-defined interface for drivers to export
fp@369: information to user space. It serves also as an relief for the process
fp@369: filesystem (Procfs), where over the years much non-process information
fp@369: was concentrated.
fp@369: 
fp@369: Sysfs exports information about devices, classes and busses via a
fp@369: virtual filesystem, usually mounted to \textit{/sys}. The EtherCAT
fp@369: master slightly differs from this concept, because the only physical
fp@369: device is the network adapter it uses for bus communication, which is
fp@369: already represented in Sysfs. For the EtherCAT bus is no system bus
fp@369: like PCI (with device and driver structures), it would not make any
fp@369: sense to represent it as bus structure in Sysfs.
fp@369: 
fp@369: Therefore, the EtherCAT master is represented as a new directory
fp@369: directly unter the Sysfs root. Every master gets its own Sysfs entry
fp@369: named \textit{ethercatX}, where X is the index of the master. Two
fp@369: masters would result in the directories \textit{/sys/ethercat0} and
fp@369: \textit{/sys/ethercat1}, respectively.
fp@369: 
fp@369: The Sysfs base class in the kernel code is the \textit{kobject}
fp@369: structure. Each object structure, that is to be represented in Sysfs,
fp@369: has to contain such a structure, because due to the concurrent access
fp@369: (through ``normal'' kernel code and Sysfs code) the object deletion
fp@369: gets a little more complicated: The object may not be freed until no
fp@369: instance uses it any more. Therefore, each kobject maintains a
fp@369: reference counter. If the reference counter gets zero, the object is
fp@369: finally freed. A kobject can be registered to appear as a directory in
fp@369: Sysfs with a call to \textit{kobject\_add()}. Each kobject type can
fp@369: define attributes, that appear as files in the kobject's
fp@369: directory. Callback functions have to be provided for reading (and
fp@369: perhaps writing) access.
fp@369: 
fp@369: \subsubsection{Master Attributes}
fp@369: \label{sec:sysfs-master}
fp@369: 
fp@369: Below is a typical listing of the masters Sysfs directory (that is a
fp@369: file system representation of the master's kobject):
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{ls /sys/ethercat0}`
fp@369:   debug_level          slave000  slave003  slave006
fp@369:   eeprom_write_enable  slave001  slave004  slave007
fp@369:   info                 slave002  slave005  slave008
fp@369: \end{lstlisting}
fp@369: 
fp@369: The following attributes exist in the master directory:
fp@369: 
fp@369: \begin{description}
fp@369: \item[debug\_level] (read/write) This attribute contains the master's
fp@369:   debug level, which controls, how much information is printed into
fp@369:   syslog. The values 0 (no additional debug messages), 1 (a few
fp@369:   additional debug messages) and 2 (all additional debug messages) are
fp@369:   defined. Writing is done with command like
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     host# `\textbf{echo 1 > /sys/ethercat0/debug\_level}`
fp@369:   \end{lstlisting}
fp@369: 
fp@369:   and is receipted with a syslog message by the master:
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     EtherCAT: Master debug level set to 1.
fp@369:   \end{lstlisting}
fp@369: 
fp@369: \item[enable\_eeprom\_writing] (read/write) See
fp@369:   section~\ref{sec:eepromaccess} for how to use this attribute.
fp@369: 
fp@369: \item[info] (read only) This attribute contains information about the
fp@369:   master. Example contents are below:
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     host> `\textbf{cat /sys/ethercat0/info}`
fp@369: 
fp@369:     Mode: IDLE
fp@369:     Slaves: 9
fp@369: 
fp@369:     Timing (min/avg/max) [us]:
fp@369:       Idle cycle: 4 / 4.38 / 34
fp@369:       EoE cycle: 9 / 11.91 / 23
fp@369: 
fp@369:     EoE statistics (RX/TX) [bps]:
fp@369:       eoe0: 0 / 3184
fp@369:   \end{lstlisting}
fp@369: 
fp@369:   The mode can be \textit{ORPHANED}, \textit{IDLE} or
fp@369:   \textit{OPERATION}. The other parameters are self-explanatory.
fp@369: 
fp@369: \end{description}
fp@369: 
fp@369: \subsubsection{Domain Attributes}
fp@369: \label{sec:sysfs-domain}
fp@369: 
fp@369: In operation mode, each created domain is represented as a directory
fp@369: \textit{domainX}, where X is the domain index. Below is a listing of
fp@369: the domain directory contents:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{ls /sys/ethercat0/domain0}`
fp@369:   image_size
fp@369: \end{lstlisting}
fp@369: 
fp@369: The domain directories currently only export the domain's image size.
fp@369: It is planned to export the whole process data mapping for debugging
fp@369: purposes.
fp@369: 
fp@369: \subsubsection{Slave Attributes}
fp@369: \label{sec:sysfs-slave}
fp@369: 
fp@369: Each slave on the bus is represented in its own directory
fp@369: \textit{slaveXXX}, where XXX is the slave's 3-digit ring position in
fp@369: the EtherCAT bus. Below is a listing of a slave directory:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{ls /sys/ethercat0/slave003}`
fp@369:   eeprom  info  state
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[eeprom] (read/write) See section~\ref{sec:eepromaccess} for how
fp@369:   to use this attribute.
fp@369: 
fp@369: \item[info] (read only) This attribute contains a bunch of information
fp@369:   about the slave. Below is an example output:
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     host> `\textbf{cat /sys/ethercat0/slave003/info}`
fp@369: 
fp@369:     Name: EL4132 2K. Ana. Ausgang +/-10V
fp@369:     Vendor ID: 0x00000002
fp@369:     Product code: 0x10243052
fp@369: 
fp@369:     State: INIT
fp@369:     Ring position: 3
fp@369:     Advanced position: 1:3
fp@369: 
fp@369:     Data link status:
fp@369:       Port 0 (EBUS) Link down, Loop open, Signal detected
fp@369:       Port 1 (EBUS) Link down, Loop open, Signal detected
fp@369:       Port 2 (EBUS) Link down, Loop closed, No signal
fp@369:       Port 3 (EBUS) Link down, Loop closed, No signal
fp@369: 
fp@369:     Mailboxes:
fp@369:       RX mailbox: 0x1800/246, TX mailbox: 0x18F6/246
fp@369:       Supported protocols: CoE, FoE
fp@369: 
fp@369:     SII data:
fp@369:       Group: AnaOut
fp@369:       Image: TERM_AO
fp@369:       Order#: EL4132
fp@369: 
fp@369:     Sync-Managers:
fp@369:       0: 0x1800, length 246, control 0x26, enable
fp@369:       1: 0x18F6, length 246, control 0x22, enable
fp@369:       2: 0x1000, length 0, control 0x24, enable
fp@369:       3: 0x1100, length 0, control 0x20, enable
fp@369: 
fp@369:     PDOs:
fp@369:       RXPDO "Channel 1" (0x1600), Sync-Manager 2
fp@369:         "Output" 0x6411:1, 16 bit
fp@369:       RXPDO "Channel 2" (0x1601), Sync-Manager 2
fp@369:         "Output" 0x6411:2, 16 bit
fp@369:   \end{lstlisting}
fp@369: 
fp@369:   This is nearly all of the SII category information needed to
fp@369:   configure the slave, supplemented with state and addressing
fp@369:   information.
fp@369: 
fp@369: \item[state] (read/write) This attribute contains the slave's state.
fp@369:   It can be read or written:
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     host# `\textbf{cat /sys/ethercat0/slave003/state}`
fp@369:     OP
fp@369:     host# `\textbf{echo SAVEOP > /sys/ethercat0/slave003/state}`
fp@369:   \end{lstlisting}
fp@369: 
fp@369:   This command should also be receipted with a syslog message:
fp@369: 
fp@369:   \begin{lstlisting}[gobble=4]
fp@369:     EtherCAT: Accepted new state SAVEOP for slave 3.
fp@369:     EtherCAT: Changing state of slave 3 from OP to SAVEOP.
fp@369:     EtherCAT: Slave states: INIT, SAVEOP, OP.
fp@369:   \end{lstlisting}
fp@369: 
fp@369:   After the new requested state was accepted from user space, the
fp@369:   operation state machine (see section~\ref{sec:fsm-op}) or the idle
fp@369:   state machine (section~\ref{sec:fsm-idle}) notices, that the
fp@369:   requested slave state differs from the current one, and therefore
fp@369:   executes the slave configuration state machine, until the slave has
fp@369:   reached the requested state.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsubsection{E$^2$PROM Access}
fp@369: \label{sec:eepromaccess}
fp@369: \index{E$^2$PROM!Access}
fp@369: 
fp@369: It is possible to directly read or write the complete E$^2$PROM
fp@369: contents of the slaves. This was introduced for the reasons below:
fp@369: 
fp@369: \begin{itemize}
fp@369: \item The format of the E$^2$PROM data is still in development and
fp@369:   categories can be added in the future. With read and write access,
fp@369:   the complete memory contents can be easily backed up and restored.
fp@369: \item Some E$^2$PROM data fields have to be altered (like the alias
fp@369:   address). A quick writing must be possible for that.
fp@369: \item Through read access, analyzing category data is possible from
fp@369:   user space.
fp@369: \end{itemize}
fp@369: 
fp@369: Reading out E$^2$PROM data is as easy as reading other
fp@369: attributes. Though the data are in binary format, analyzation is
fp@369: easier with a tool like \textit{hexdump}:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{cat /sys/ethercat0/slave003/eeprom | hexdump}`
fp@369:   0000000 0103 0000 0000 0000 0000 0000 0000 008c
fp@369:   0000010 0002 0000 3052 07f0 0000 0000 0000 0000
fp@369:   0000020 0000 0000 0000 0000 0000 0000 0000 0000
fp@369:   ...
fp@369: \end{lstlisting}
fp@369: 
fp@369: Backing up E$^2$PROM contents gets as easy as copying a file:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{cp /sys/ethercat0/slave003/eeprom slave003.eep}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: Writing access is only possible as \textit{root}. Moreover writing has
fp@369: to be explicitly enabled and is only allowed in idle mode. This is a
fp@369: safety measure, because without the correct memory contents, a slave
fp@369: is unusable. Writing E$^2$PROM contents in operation mode is not
fp@369: provided yet.
fp@369: 
fp@369: E$^2$PROM writing is enabled with the command below:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{echo 1 > /sys/ethercat0/eeprom\_write\_enable}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: The success can be seen in the syslog messages again:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   EtherCAT: Slave EEPROM writing enabled.
fp@369: \end{lstlisting}
fp@369: 
fp@369: Now, it is possible to write E$^2$PROM contents to a slave. The master
fp@369: will accept data through the \textit{eeprom} file and will perform a
fp@369: short validation of the contents, before starting the write operation.
fp@369: This validation checks the complete size and the category headers.
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{cat slave003.eep > /sys/ethercat0/slave003/eeprom}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: The write operation can take a few seconds.
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   EtherCAT: EEPROM writing scheduled for slave 3, 88 words.
fp@369:   EtherCAT: Writing EEPROM of slave 3...
fp@369:   EtherCAT: Finished writing EEPROM of slave 3.
fp@369: \end{lstlisting}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{User Space Tools}
fp@369: \index{User space!Tools}
fp@369: 
fp@369: There is a user space tool called \textit{lsec}\index{lsec} (``List
fp@369: EtherCAT'') to visualize the EtherCAT bus. Running it usually results
fp@369: in an output like this:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{lsec}`
fp@369:   EtherCAT bus listing for master 0:
fp@369:      0  1:0  OP      EK1100 Ethernet Kopplerklemme (2A E-Bus)
fp@369:      1  1:1  INIT    EL4132 2K. Ana. Ausgang +/-10V
fp@369:      2  1:2  INIT    EL4132 2K. Ana. Ausgang +/-10V
fp@369:      3  1:3  SAVEOP  EL4132 2K. Ana. Ausgang +/-10V
fp@369:      4  1:4  INIT    EL5101 Incremental Encoder Interface
fp@369:      5  1:5  INIT    EL1014 4K. Dig. Eingang 24V, 10s
fp@369:      6  1:6  OP      EL6601 1 Port Switch (Ethernet, CoE)
fp@369:      7  1:7  INIT    EL5101 Incremental Encoder Interface
fp@369:      8  1:8  INIT    EL5001 1K. SSI Encoder
fp@369: \end{lstlisting}
fp@369: 
fp@369: Every slave is displayed as one text row. The first column shows its
fp@369: ring position, the second displays the ``advanced position address''
fp@369: (see section~\ref{sec:addr}) and the third column displays the current
fp@369: slave state. The last column is the slave's name, as it appears in the
fp@369: ``general'' E$^2$PROM category.
fp@369: 
fp@369: The lsec program is a Perl script, that evaluates the Sysfs
fp@369: \textit{info} attributes of the slaves (see
fp@369: section~\ref{sec:sysfs-slave}). This is done for master $0$ by
fp@369: default, but the master index can be specified via command line:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host> `\textbf{lsec -h}`
fp@369:   Usage: ec_list [OPTIONS]
fp@369:           -m <IDX>    Query master <IDX>.
fp@369:           -h          Show this help.
fp@369: \end{lstlisting}
fp@369: 
fp@369: This script has proved as useful for troubleshooting: If it displays
fp@369: slaves, the master is up and running, and the bus connection is
fp@369: present, too. It is also useful when building up a bus: It can verify
fp@369: the list of slaves and help to create a process data image (see
fp@369: chapter~\ref{chapter:usage}).
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{System Integration}
fp@369: \label{sec:system}
fp@369: 
fp@369: To integrate the EtherCAT master into a running system, it has to be
fp@369: guaranteed, that it is started on system startup. In addition, there has
fp@369: to be a persistent configuration, that is also applied on startup.
fp@369: 
fp@369: \subsubsection{The EtherCAT Init Script}
fp@369: \label{sec:init}
fp@369: \index{Init script}
fp@369: 
fp@369: The EtherCAT master provides an ``init script'', that conforms to the
fp@369: requirements of the ``Linux Standard Base'' (LSB\index{LSB},
fp@374: \cite{lsb}). The script is installed to \textit{etc/init.d/ethercat}
fp@374: below the installation prefix and has to be copied to the appropriate
fp@374: location (see section~\ref{sec:make}), before the master can be
fp@374: inserted as a service. The different Linux distributions offer
fp@374: different ways to mark the service for starting and stopping in
fp@374: certain runlevels (for example, SUSE Linux provides the
fp@374: \textit{insserv} command).
fp@369: 
fp@369: To provide service dependencies (i.~e. which services have to be
fp@369: started before) right inside the init script code, LSB defines a
fp@369: special comment block. System tools can extract this information to
fp@369: insert the EtherCAT init script at the correct place in the startup
fp@369: sequence:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   ### BEGIN INIT INFO
fp@369:   # Provides:          ethercat
fp@369:   # Required-Start:    $local_fs $syslog $network
fp@369:   # Should-Start:      $time
fp@369:   # Required-Stop:     $local_fs $syslog $network
fp@369:   # Should-Stop:       $time
fp@369:   # Default-Start:     3 5
fp@369:   # Default-Stop:      0 1 2 6
fp@369:   # Short-Description: EtherCAT master modules
fp@369:   # Description:
fp@369:   ### END INIT INFO
fp@369: \end{lstlisting}
fp@369: 
fp@369: The init script can also be used for manually starting and stopping
fp@369: the EtherCAT master. It has to be executed with one of the parameters
fp@369: \textit{start}, \textit{stop}, \textit{restart} or \textit{status}.
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{/etc/init.d/ethercat restart}`
fp@369:   Shutting down EtherCAT master                done
fp@369:   Starting EtherCAT master                     done
fp@369: \end{lstlisting}
fp@369: 
fp@369: \subsubsection{The EtherCAT Sysconfig File}
fp@369: \label{sec:sysconfig}
fp@369: \index{Sysconfig file}
fp@369: 
fp@369: For persistent configuration, the init script uses a sysconfig file
fp@374: installed to \textit{etc/sysconfig/ethercat} (below the installation
fp@374: prefix), that is mandatory for the init script. The sysconfig file
fp@374: contains all configuration variables needed to operate a master:
fp@369: 
fp@369: \begin{description}
fp@369: \item[DEVICE\_INDEX] This variable must contain the PCI index of the
fp@369:   EtherCAT device.  Setting this is mandatory for the EtherCAT init
fp@369:   script. Default: $-1$
fp@369: \item[EOE\_INTERFACES] The number of virtual Ethernet-over-EtherCAT
fp@369:   interfaces, every master creates on startup. See
fp@369:   section~\ref{sec:eoeimp}. Default: $0$
fp@369: \item[EOE\_BRIDGE] If this variable is set, all EoE interfaces will be
fp@369:   added to a network bridge according to IEEE 802.1D after master
fp@369:   startup. The variable must contain the name of the bridge. To use
fp@369:   this functionality, the kernel must be configured with the
fp@369:   \textit{CONFIG\_BRIDGE} option and the \textit{bridge-utils} package
fp@369:   must be installed (i.~e. the \textit{brctl} command is needed).
fp@369: \item[EOE\_IP\_ADDRESS] The IP address of the EoE bridge. Setting this
fp@369:   together with \textit{EOE\_IP\_NETMASK} will let the local host
fp@369:   communicate with devices on the EoE bridge.
fp@369: \item[EOE\_IP\_NETMASK] IP netmask of the EoE bridge.
fp@369: \item[EOE\_EXTRA\_INTERFACES] The list of extra interfaces to include
fp@369:   in the EoE brid\-ge. Set this to interconnect the EoE bridge with
fp@369:   other local interfaces. If \textit{EOE\_\-BRIDGE} is empty or
fp@369:   undefined, setting this variable has no effect. Important: The IP
fp@369:   address of the listed interfaces will be cleared. Setting
fp@369:   \textit{EOE\_\-IP\_\-ADDRESS} and \textit{EOE\_IP\_NETMASK} will
fp@369:   re-enable them for IP traffic.
fp@369: \item[EOE\_GATEWAY] The IP address of the default gateway. If this
fp@369:   variable is set, the gateway will be renewed after bridge
fp@369:   installation. This is necessary, if the default gateway's interface
fp@369:   is one of the \textit{EOE\_EXTRA\_INTERFACES}.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Monitoring and Debugging}
fp@369: \label{sec:debug}
fp@369: \index{Monitoring}
fp@369: 
fp@369: For debugging purposes, every EtherCAT master registeres a read-only
fp@369: network interface \textit{ecX}, where X is a number, provided by the
fp@369: kernel on device registration. While it is ``up'', the master forwards
fp@369: every frame sent and received to this interface.
fp@369: 
fp@369: This makes it possible to connect an network monitor (like Wireshark
fp@369: or tcpdump) to the debug interface and monitor the EtherCAT frames.
fp@369: 
fp@369: It has to be considered, that can be frame rate can be very high. The
fp@369: idle state machine usually runs every kernel timer interrupt (up to
fp@369: $1$~kHz) and with a connected realtime module, the rate can be even
fp@369: higher.
fp@369: 
fp@369: \paragraph{Attention:} The socket buffers needed for the operation of
fp@369: the debugging interface have to be allocated dynamically. Some Linux
fp@369: realtime extensions do not allow this in realtime context!
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Timing Aspects}
fp@369: \label{sec:timing}
fp@369: 
fp@369: Although EtherCAT's timing is highly deterministic and therefore
fp@369: timing issues are rare, there are a few aspects that can (and should
fp@369: be) dealt with.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Realtime Interface Profiling}
fp@369: \label{sec:timing-profile}
fp@369: \index{Realtime!Profiling}
fp@369: 
fp@369: One of the most important timing aspects are the runtimes of the
fp@369: realtime interface functions, that are called in cyclic context. These
fp@369: functions make up an important part of the overall timing of the
fp@369: realtime module. To measure the timing of the functions, the following
fp@369: code was used:
fp@369: 
fp@369: \begin{lstlisting}[gobble=2,language=C]
fp@369:   c0 = get_cycles();
fp@369:   ecrt_master_receive(master);
fp@369:   c1 = get_cycles();
fp@369:   ecrt_domain_process(domain1);
fp@369:   c2 = get_cycles();
fp@369:   ecrt_master_run(master);
fp@369:   c3 = get_cycles();
fp@369:   ecrt_master_send(master);
fp@369:   c4 = get_cycles();
fp@369: \end{lstlisting}
fp@369: 
fp@369: Between each call of an interface function, the CPU timestamp counter
fp@369: is read. The counter differences are converted to microseconds with
fp@369: help of the \textit{cpu\_khz} variable, that contains the number of
fp@369: increments per millisecond.
fp@369: 
fp@369: For the actual measuring, a system with a $2.0$~GHz CPU was used, that
fp@369: ran the above code in an RTAI thread with a cycle time of $100$
fp@369: \textmu s.  The measuring was repeated $n = 100$ times and the results
fp@369: were averaged. These can be seen in table~\ref{tab:profile}.
fp@369: 
fp@369: \begin{table}[htpb]
fp@369:   \centering
fp@369:   \caption{Profiling of a Realtime Cycle on a $2.0$~GHz Processor}
fp@369:   \label{tab:profile}
fp@369:   \vspace{2mm}
fp@369:   \begin{tabular}{l|r|r}
fp@369:     Element & Mean Duration [\textmu s] & Standard Deviancy [\textmu s] \\
fp@369:     \hline
fp@369:     \textit{ecrt\_master\_receive()} & 8.04 & 0.48\\
fp@369:     \textit{ecrt\_domain\_process()} & 0.14 & 0.03\\
fp@369:     \textit{ecrt\_master\_run()} & 0.29 & 0.12\\
fp@369:     \textit{ecrt\_master\_send()} & 2.18 & 0.17\\ \hline
fp@369:     Complete Cycle & 10.65 & 0.69\\ \hline
fp@369:   \end{tabular}
fp@369: \end{table}
fp@369: 
fp@369: It is obvious, that the the functions accessing hardware make up the
fp@369: lion's share. The \textit{ec\_master\_receive()} executes the ISR of
fp@369: the Ethernet device, analyzes datagrams and copies their contents into
fp@369: the memory of the datagram objects. The \textit{ec\_master\_send()}
fp@369: assembles a frame out of different datagrams and copies it to the
fp@369: hardware buffers. Interestingly, this makes up only a quarter of the
fp@369: receiving time.
fp@369: 
fp@369: The functions that only operate on the masters internal data
fp@369: structures are very fast ($\Delta t < 1$~\textmu s). Interestingly the
fp@369: runtime of \textit{ec\_domain\_process()} has a small standard
fp@369: deviancy relative to the mean value, while this ratio is about twice
fp@369: as big for \textit{ec\_master\_run()}: This probably results from the
fp@369: latter function having to execute code depending on the current state
fp@369: and the different state functions are more or less complex.
fp@369: 
fp@369: For a realtime cycle makes up about $10$~\textmu s, the theoretical
fp@369: frequency can be up to $100$~kHz. For two reasons, this frequency
fp@369: keeps being theoretical:
fp@369: 
fp@369: \begin{enumerate}
fp@369: \item The processor must still be able to run the operating system
fp@369:   between the realtime cycles.
fp@369: \item The EtherCAT frame must be sent and received, before the next
fp@369:   realtime cycle begins. The determination of the bus cycle time is
fp@369:   difficult and covered in section~\ref{sec:timing-bus}.
fp@369: \end{enumerate}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \subsection{Bus Cycle Measuring}
fp@369: \label{sec:timing-bus}
fp@369: \index{Bus cycle}
fp@369: 
fp@369: For measuring the time, a frame is ``on the wire'', two timestamps
fp@369: must be be taken:
fp@369: 
fp@369: \begin{enumerate}
fp@369: \item The time, the Ethernet hardware begins with physically sending
fp@369:   the frame.
fp@369: \item The time, the frame is completely received by the Ethernet
fp@369:   hardware.
fp@369: \end{enumerate}
fp@369: 
fp@369: Both times are difficult to determine. The first reason is, that the
fp@369: interrupts are disabled and the master is not notified, when a frame
fp@369: is sent or received (polling would distort the results). The second
fp@369: reason is, that even with interrupts enabled, the time from the event
fp@369: to the notification is unknown. Therefore the only way to confidently
fp@369: determine the bus cycle time is an electrical measuring.
fp@369: 
fp@369: Anyway, the bus cycle time is an important factor when designing
fp@369: realtime code, because it limits the maximum frequency for the cyclic
fp@369: part of the realtime module. In practice, these timing parameters are
fp@369: highly dependent on the hardware and often a trial and error method
fp@369: must be used to determine the limits of the system.
fp@369: 
fp@369: The central question is: What happens, if the cycle frequency is too
fp@369: high? The answer is, that the EtherCAT frames that have been sent at
fp@369: the end of the cycle are not yet received, when the next cycle starts.
fp@369: First this is noticed by \textit{ecrt\_domain\_process()}, because the
fp@369: working counter of the process data datagrams were not increased. The
fp@369: function will notify the user via syslog\footnote{To limit syslog
fp@369:   output, a mechanism has been implementet, that outputs a summarized
fp@369:   notification at maximum once a second.}. In this case, the process
fp@369: data keeps being the same as in the last cycle, because it is not
fp@369: erased by the domain. When the domain datagrams are queued again, the
fp@369: master notices, that they are already queued (and marked as sent). The
fp@369: master will mark them as unsent again and output a warning, that
fp@369: datagrams were ``skipped''.
fp@369: 
fp@369: On the mentioned $2.0$~GHz system, the possible cycle frequency can be
fp@369: up to $25$~kHz without skipped frames. This value can surely be
fp@369: increased by choosing faster hardware. Especially the RealTek network
fp@369: hardware could be replaced by a faster one. Besides, implementing a
fp@369: dedicated ISR for EtherCAT devices would also contribute to increasing
fp@369: the latency. These are two points on the author's to-do list.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \chapter{Using the EtherCAT Master}
fp@369: \label{chapter:usage}
fp@369: \index{Master!Usage}
fp@369: 
fp@369: This chapter will give practical examples of how to use the EtherCAT
fp@369: master via the realtime interface by writing a realtime module.
fp@369: 
fp@369: Section~\ref{sec:make} shows how to compile and install the master,
fp@369: while the sections~\ref{sec:mini} to~\ref{sec:concurrency} give
fp@369: examples for different realtime modules.
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Compiling and Installing}
fp@369: \label{sec:make}
fp@369: \index{Master!Compilation}
fp@369: 
fp@369: The current EtherCAT master code is available at~\cite{etherlab}.
fp@369: After downloading the \textit{tar.bz2} file, it has to be unpacked
fp@369: with the command below (or similar):
fp@369: 
fp@369: \begin{lstlisting}
fp@374:   host> `\textbf{tar xjf ethercat-1.1-rXXX.tar.bz2}`
fp@374:   host> `\textbf{cd ethercat-1.1-rXXX/}`
fp@374: \end{lstlisting}
fp@374: 
fp@374: The tarball was created with GNU Autotools, so the build process
fp@374: follows the usual commands:
fp@369: 
fp@369: \begin{lstlisting}
fp@374:   host> `\textbf{./configure}`
fp@374:   host> `\textbf{make}`
fp@374: \end{lstlisting}
fp@374: 
fp@374: The default installation prefix is \textit{/opt/etherlab}. It can be
fp@374: changed with the \texttt{--prefix} argument.
fp@374: 
fp@374: Linux kernel sources are needed for compilation\footnote{If a realtime
fp@374:   extension shall to be used, the kernel should be patched before
fp@374:   compiling the EtherCAT master.}. To compile the EtherCAT master
fp@374: modules for a different kernel than the running kernel, the target
fp@374: kernel version can be specified with the \texttt{--with-linux}
fp@374: argument. Example:
fp@369: 
fp@369: \begin{lstlisting}
fp@374:   host> `\textbf{./configure --with-linux="2.6.17-ipipe"}`
fp@369:   host> `\textbf{make}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: The following commands have to be entered as \textit{root}: To install
fp@374: the kernel modules, headers, the init script, the sysconfig file and
fp@374: the user space tools, the below command has to be executed:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{make install}`
fp@369: \end{lstlisting}
fp@369: 
fp@374: If the EtherCAT master shall be run as a service (recommended), the
fp@374: init script and the sysconfig file have to be copied to the
fp@374: appropriate locations. The below example is suitable for SUSE Linux.
fp@374: It may vary for other distributions.
fp@374: 
fp@374: \begin{lstlisting}
fp@374:   host# `\textbf{cd /opt/etherlab}`
fp@374:   host# `\textbf{cp etc/sysconfig/ethercat /etc/sysconfig/}`
fp@374:   host# `\textbf{cp etc/init.d/ethercat /etc/init.d/}`
fp@374:   host# `\textbf{insserv ethercat}`
fp@374: \end{lstlisting}
fp@374: 
fp@374: Now the sysconfig file has to be customized. For the contents of the
fp@374: file, see section~\ref{sec:sysconfig}. To give a short summary: The
fp@374: most important thing is to adjust the \textit{DEVICE\_INDEX} variable.
fp@374: It has to be set to the index of the compatible network device to use
fp@369: with EtherCAT, where the order of devices is dependent on their
fp@369: position in the PCI bus. If this is not known, the index can be
fp@369: determinded with trial and error, but it has to be considered that a
fp@369: wrong value can cause a loss of network connection.
fp@369: 
fp@369: After the basic configuration is done, the master can be started with
fp@369: the below command:
fp@369: 
fp@369: \begin{lstlisting}
fp@369:   host# `\textbf{/etc/init.d/ethercat start}`
fp@369: \end{lstlisting}
fp@369: 
fp@369: The operation of the master can be observed by looking at the
fp@374: syslog\index{syslog} messages, which should look like the ones below.
fp@374: If EtherCAT slaves are connected to the master's EtherCAT device, the
fp@374: activity indicators should begin to flash.
fp@369: 
fp@369: \begin{lstlisting}[numbers=left]
fp@369:   EtherCAT: Master driver, 1.1 (stable) - rev. 513,
fp@369:       compiled by fp at Aug 09 2006 10:23:20
fp@369:   EtherCAT: Initializing 1 EtherCAT master(s)...
fp@369:   EtherCAT: Initializing master 0.
fp@369:   EtherCAT: Master driver initialized.
fp@369:   ec_8139too Fast Ethernet driver 0.9.27 Revision 513,
fp@369:       compiled by fp at Aug 09 2006 10:23:20
fp@369:   ec_device_index is 0
fp@369:   ACPI: PCI Interrupt 0000:01:00.0[A] -> Link [LNKC]
fp@369:       -> GSI 11 (level, low) -> IRQ 11
fp@369:   ec0: RealTek RTL8139 at 0xd047c000, 00:c0:26:00:c6:aa, IRQ 11
fp@369:   ec0:  Identified 8139 chip type 'RTL-8100B/8139D'
fp@369:   Registering EtherCAT device...
fp@369:   Starting EtherCAT device...
fp@369:   EtherCAT: Link state changed to UP.
fp@369:   EtherCAT: Starting Idle mode.
fp@369:   EtherCAT: 11 slaves responding.
fp@369:   EtherCAT: Slave states: INIT, OP.
fp@369:   EtherCAT: Scanning bus.
fp@369:   EtherCAT: Bus scanning completed.
fp@369:   EtherCAT: No EoE handlers coupled.
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1}] The master module is loaded,
fp@369:   and one master is initialized.
fp@369: \item[\normalfont\textcircled{\tiny 6}] The EtherCAT-capable RTL8139
fp@369:   device driver is loaded. It connects its first network device to the
fp@369:   master.
fp@369: \item[\normalfont\textcircled{\tiny 16}] The master starts idle mode
fp@369:   and begins scanning the bus for slaves.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{A Minimal Example Module}
fp@369: \label{sec:mini}
fp@369: \index{Examples!Minimal}
fp@369: 
fp@369: This section will explain the usage of the EtherCAT master from a
fp@369: minimal kernel module. The complete module code is obtainable as a
fp@369: part of the EtherCAT master code release (see~\cite{etherlab}, file
fp@369: \textit{examples/mini/mini.c}).
fp@369: 
fp@369: The minimal example uses a kernel timer (software interrupt) to handle
fp@369: cyclic code. After the timer function is executed, it re-adds itself
fp@369: with a delay of one \textit{jiffy}\index{jiffies}, which results in a
fp@369: timer frequency of \textit{HZ}\nomenclature{HZ}{Kernel macro
fp@369:   containing the timer interrupt frequency}
fp@369: 
fp@369: The module-global variables, needed to operate the master can be seen
fp@369: in listing~\ref{lst:minivar}.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Minimal
fp@369:     variables},label=lst:minivar]
fp@369:   struct timer_list timer;
fp@369: 
fp@369:   ec_master_t *master = NULL;
fp@369:   ec_domain_t *domain1 = NULL;
fp@369: 
fp@369:   void *r_dig_in, *r_ana_out;
fp@369: 
fp@369:   ec_pdo_reg_t domain1_pdos[] = {
fp@369:           {"1", Beckhoff_EL1014_Inputs, &r_dig_in},
fp@369:           {"2", Beckhoff_EL4132_Ouput1, &r_ana_out},
fp@369:           {}
fp@369:   };
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1}] There is a timer object
fp@369:   declared, that is needed to tell the kernel to install a timer and
fp@369:   execute a certain function, if it runs out. This is done by a
fp@369:   variable of the \textit{timer\_list} structure.
fp@369: \item[\normalfont\textcircled{\tiny 3} -- \textcircled{\tiny 4}] There
fp@369:   is a pointer declared, that will later point to a requested EtherCAT
fp@369:   master.  Additionally there is a pointer to a domain object needed,
fp@369:   that will manage process data IO.
fp@369: \item[\normalfont\textcircled{\tiny 6}] The pointers \textit{r\_*}
fp@369:   will later point to the \underline{r}aw process data values inside
fp@369:   the domain memory. The addresses they point to will be set during a
fp@369:   call to \textit{ec\_\-master\_\-activate()}, that will create the
fp@369:   domain memory and configure the mapped process data image.
fp@369: \item[\normalfont\textcircled{\tiny 8} -- \textcircled{\tiny 12}] The
fp@369:   configuration of the mapping of certain PDOs in a domain can easily
fp@369:   be done with the help of an initialization array of the
fp@369:   \textit{ec\_pdo\_reg\_t} type, defined as part of the realtime
fp@369:   interface. Each record must contain the ASCII bus-address of the
fp@369:   slave (see section~\ref{sec:addr}), the slave's vendor ID and
fp@369:   product code, and the index and subindex of the PDO to map (these
fp@369:   four fields can be specified in junction, by using one of the
fp@369:   defines out of the \textit{include/ecdb.h} header). The last field
fp@369:   has to be the address of the process data pointer, so it can later
fp@369:   be redirected appropriately. Attention: The initialization array
fp@369:   must end with an empty record (\textit{\{\}})!
fp@369: \end{description}
fp@369: 
fp@369: The initialization of the minimal realtime module is done by the
fp@369: ``Minimal init function'' in listing~\ref{lst:miniinit}.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Minimal init
fp@369:     function},label={lst:miniinit}]
fp@369:   int __init init_mini_module(void)
fp@369:   {
fp@369:           if (!(master = ecrt_request_master(0))) {
fp@369:                   goto out_return;
fp@369:           }
fp@369: 
fp@369:           if (!(domain1 = ecrt_master_create_domain(master))) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           if (ecrt_domain_register_pdo_list(domain1,
fp@369:                                             domain1_pdos)) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           if (ecrt_master_activate(master)) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           ecrt_master_prepare(master);
fp@369: 
fp@369:           init_timer(&timer);
fp@369:           timer.function = run;
fp@369:           timer.expires = jiffies + 10;
fp@369:           add_timer(&timer);
fp@369: 
fp@369:           return 0;
fp@369: 
fp@369:         out_release_master:
fp@369:           ecrt_release_master(master);
fp@369:         out_return:
fp@369:           return -1;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] It is tried to request the
fp@369:   first EtherCAT master (index 0). On success, the
fp@369:   \textit{ecrt\_\-request\_\-master()} function returns a pointer to
fp@369:   the reserved master, that can be used as an object to following
fp@369:   functions calls. On failure, the function returns \textit{NULL}.
fp@369: \item[\normalfont\textcircled{\tiny 7}] In order to exchange process
fp@369:   data, a domain object has to be created. The
fp@369:   \textit{ecrt\_\-master\_\-create\_domain()} function also returns a
fp@369:   pointer to the created domain, or \textit{NULL} in error case.
fp@369: \item[\normalfont\textcircled{\tiny 11}] The registration of domain
fp@369:   PDOs with an initialization array results in a single function call.
fp@369:   Alternatively the data fields could be registered with individual
fp@369:   calls of \textit{ecrt\_domain\_register\_pdo()}.
fp@369: \item[\normalfont\textcircled{\tiny 16}] After the configuration of
fp@369:   process data mapping, the master can be activated for cyclic
fp@369:   operation. This will configure all slaves and bring them into
fp@369:   \textit{OP} state.
fp@369: \item[\normalfont\textcircled{\tiny 20}] This call is needed to avoid
fp@369:   a case differentiation in cyclic operation: The first operation in
fp@369:   cyclic mode is a receive call. Due to the fact, that there is
fp@369:   nothing to receive during the first cycle, there had to be an
fp@369:   \textit{if}-statement to avoid a warning. A call to
fp@369:   \textit{ec\_master\_prepare()} sends a first datagram containing a
fp@369:   process data exchange datagram, so that the first receive call will
fp@369:   not fail.
fp@369: \item[\normalfont\textcircled{\tiny 22} -- \textcircled{\tiny 25}] The
fp@369:   master is now ready for cyclic operation. The kernel timer that
fp@369:   cyclically executes the \textit{run()} function is initialized and
fp@369:   started.
fp@369: \end{description}
fp@369: 
fp@369: The coding of a cleanup function fo the minimal module can be seen in
fp@369: listing~\ref{lst:miniclean}.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Minimal cleanup
fp@369:     function},label={lst:miniclean}]
fp@369:   void __exit cleanup_mini_module(void)
fp@369:   {
fp@369:           del_timer_sync(&timer);
fp@369:           ecrt_master_deactivate(master);
fp@369:           ecrt_release_master(master);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] To cleanup the module, it it
fp@369:   necessary to stop the cyclic processing. This is done by a call to
fp@369:   \textit{del\_timer\_sync()} which safely removes a queued timer
fp@369:   object. It is assured, that no cyclic work will be done after this
fp@369:   call returns.
fp@369: \item[\normalfont\textcircled{\tiny 4}] This call deactivates the
fp@369:   master, which results in all slaves being brought to their
fp@369:   \textit{INIT} state again.
fp@369: \item[\normalfont\textcircled{\tiny 5}] This call releases the master,
fp@369:   removes any existing configuration and silently starts the idle
fp@369:   mode. The value of the master pointer is invalid after this call and
fp@369:   the module can be safely unloaded.
fp@369: \end{description}
fp@369: 
fp@369: The final part of the minimal module is that for the cyclic work. Its
fp@369: coding can be seen in listing~\ref{lst:minirun}.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Minimal cyclic
fp@369:     function},label={lst:minirun}]
fp@369:   void run(unsigned long data)
fp@369:   {
fp@369:           static uint8_t dig_in_0;
fp@369: 
fp@369:           ecrt_master_receive(master);
fp@369:           ecrt_domain_process(domain1);
fp@369: 
fp@369:           dig_in_0 = EC_READ_BIT(r_dig_in, 0);
fp@369:           EC_WRITE_S16(r_ana_out, dig_in_0 * 0x3FFF);
fp@369: 
fp@369:           ecrt_master_run(master);
fp@369:           ecrt_master_send(master);
fp@369: 
fp@369:           timer.expires += 1; // frequency = HZ
fp@369:           add_timer(&timer);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 5}] The cyclic processing starts
fp@369:   with receiving datagrams, that were sent in the last cycle. The
fp@369:   frames containing these datagrams have to be received by the network
fp@369:   interface card prior to this call.
fp@369: \item[\normalfont\textcircled{\tiny 6}] The process data of domain 1
fp@369:   has been automatically copied into domain memory while datagram
fp@369:   reception. This call checks the working counter for changes and
fp@369:   re-queues the domain's datagram for sending.
fp@369: \item[\normalfont\textcircled{\tiny 8}] This is an example for reading
fp@369:   out a bit-oriented process data value (i.~e. bit 0) via the
fp@369:   \textit{EC\_READ\_BIT()} macro. See section~\ref{sec:macros} for
fp@369:   more information about those macros.
fp@369: \item[\normalfont\textcircled{\tiny 9}] This line shows how to write a
fp@369:   signed, 16-bit process data value. In this case, the slave is able
fp@369:   to output voltages of $-10$~V to $+10$~V with a resolution of 16
fp@369:   bit.  This write command outputs either $0$~V or $+5$~V, depending
fp@369:   of the value of \textit{dig\_in\_0}.
fp@369: \item[\normalfont\textcircled{\tiny 11}] This call runs the master's
fp@369:   operation state machine (see section~\ref{sec:fsm-op}). A single
fp@369:   state is processed, and datagrams are queued. Mainly bus observation
fp@369:   is done: The bus state is determined and in case of slaves that lost
fp@369:   their configuration, reconfiguration is tried.
fp@369: \item[\normalfont\textcircled{\tiny 12}] This method sends all queued
fp@369:   datagrams, in this case the domain's datagram and one of the master
fp@369:   state machine. In best case, all datagrams fit into one frame.
fp@369: \item[\normalfont\textcircled{\tiny 14} -- \textcircled{\tiny 15}]
fp@369:   Kernel timers are implemented as ``one-shot'' timers, so they have
fp@369:   to be re-added after each execution. The time of the next execution
fp@369:   is specified in \textit{jiffies} and will happen at the time of the
fp@369:   next system timer interrupt. This results in the \textit{run()}
fp@369:   function being executed with a frequency of \textit{HZ}.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{An RTAI Example Module}
fp@369: \label{sec:rtai}
fp@369: \index{Examples!RTAI}
fp@369: 
fp@369: The whole code can be seen in the EtherCAT master code release
fp@369: (see~\cite{etherlab}, file \textit{examples/rtai/rtai\_sample.c}).
fp@369: 
fp@369: Listing~\ref{lst:rtaivar} shows the defines and global variables
fp@369: needed for a minimal RTAI module with EtherCAT processing.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI task
fp@369:     declaration},label={lst:rtaivar}]
fp@369:   #define FREQUENCY 10000
fp@369:   #define TIMERTICKS (1000000000 / FREQUENCY)
fp@369: 
fp@369:   RT_TASK task;
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1} -- \textcircled{\tiny 2}] RTAI
fp@369:   takes the cycle period as nanoseconds, so the easiest way is to
fp@369:   define a frequency and convert it to a cycle time in nanoseconds.
fp@369: \item[\normalfont\textcircled{\tiny 4}] The \textit{task} variable
fp@369:   later contains information about the running RTAI task.
fp@369: \end{description}
fp@369: 
fp@369: Listing~\ref{lst:rtaiinit} shows the module init function for the RTAI
fp@369: module. Most lines are the same as in listing~\ref{lst:miniinit},
fp@369: differences come up when starting the cyclic code.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI module init
fp@369:     function},label={lst:rtaiinit}]
fp@369:   int __init init_mod(void)
fp@369:   {
fp@369:           RTIME requested_ticks, tick_period, now;
fp@369: 
fp@369:           if (!(master = ecrt_request_master(0))) {
fp@369:                   goto out_return;
fp@369:           }
fp@369: 
fp@369:           if (!(domain1 = ecrt_master_create_domain(master))) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           if (ecrt_domain_register_pdo_list(domain1,
fp@369:                                             domain1_pdos)) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           if (ecrt_master_activate(master)) {
fp@369:                   goto out_release_master;
fp@369:           }
fp@369: 
fp@369:           ecrt_master_prepare(master);
fp@369: 
fp@369:           requested_ticks = nano2count(TIMERTICKS);
fp@369:           tick_period = start_rt_timer(requested_ticks);
fp@369: 
fp@369:           if (rt_task_init(&task, run, 0, 2000, 0, 1, NULL)) {
fp@369:                   goto out_stop_timer;
fp@369:           }
fp@369: 
fp@369:           now = rt_get_time();
fp@369:           if (rt_task_make_periodic(&task, now + tick_period,
fp@369:                                     tick_period)) {
fp@369:                   goto out_stop_task;
fp@369:           }
fp@369: 
fp@369:           return 0;
fp@369: 
fp@369:       out_stop_task:
fp@369:           rt_task_delete(&task);
fp@369:       out_stop_timer:
fp@369:           stop_rt_timer();
fp@369:       out_deactivate:
fp@369:           ecrt_master_deactivate(master);
fp@369:       out_release_master:
fp@369:           ecrt_release_master(master);
fp@369:       out_return:
fp@369:           return -1;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 24} -- \textcircled{\tiny 25}] The
fp@369:   nanoseconds are converted to RTAI timer ticks and an RTAI timer is
fp@369:   started.  \textit{tick\_period} will be the ``real'' number of ticks
fp@369:   used for the timer period (which can be different to the requested
fp@369:   one).
fp@369: \item[\normalfont\textcircled{\tiny 27}] The RTAI task is initialized
fp@369:   by specifying the cyclic function, the parameter to hand over, the
fp@369:   stack size, priority, a flag that tells, if the function will use
fp@369:   floating point operations and a signal handler.
fp@369: \item[\normalfont\textcircled{\tiny 32}] The task is made periodic by
fp@369:   specifying a start time and a period.
fp@369: \end{description}
fp@369: 
fp@369: The cleanup function of the RTAI module in listing~\ref{lst:rtaiclean}
fp@369: is nearly as simple as that of the minimal module.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI module
fp@369:     cleanup function},label={lst:rtaiclean}]
fp@369:   void __exit cleanup_mod(void)
fp@369:   {
fp@369:           rt_task_delete(&task);
fp@369:           stop_rt_timer();
fp@369:           ecrt_master_deactivate(master);
fp@369:           ecrt_release_master(master);
fp@369:           rt_sem_delete(&master_sem);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 2}] The RTAI task will be stopped
fp@369:   and deleted.
fp@369: \item[\normalfont\textcircled{\tiny 3}] After that, the RTAI timer can
fp@369:   be stopped.
fp@369: \end{description}
fp@369: 
fp@369: The rest is the same as for the minimal module.
fp@369: 
fp@369: Worth to mention is, that the cyclic function of the RTAI module
fp@369: (listing~\ref{lst:rtairun}) has a slightly different architecture. The
fp@369: function is not executed until returning for every cycle, but has an
fp@369: infinite loop in it, that is placed in a waiting state for the rest of
fp@369: each cycle.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI module cyclic
fp@369:     function},label={lst:rtairun}]
fp@369:   void run(long data)
fp@369:   {
fp@369:           while (1) {
fp@369:                   ecrt_master_receive(master);
fp@369:                   ecrt_domain_process(domain1);
fp@369: 
fp@369:                   k_pos = EC_READ_U32(r_ssi_input);
fp@369: 
fp@369:                   ecrt_master_run(master);
fp@369:                   ecrt_master_send(master);
fp@369: 
fp@369:                   rt_task_wait_period();
fp@369:           }
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] The \textit{while (1)} loop
fp@369:   executes for the lifetime of the RTAI task.
fp@369: \item[\normalfont\textcircled{\tiny 12}] The
fp@369:   \textit{rt\_task\_wait\_period()} function sets the process into a
fp@369:   sleeping state until the beginning of the next cycle. It also
fp@369:   checks, if the cyclic function has to be terminated.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \section{Concurrency Example}
fp@369: \label{sec:concurrency}
fp@369: \index{Examples!Concurrency}
fp@369: 
fp@369: As mentioned before, there can be concurrent access to the EtherCAT
fp@369: master. The realtime module and a EoE\index{EoE} process can compete
fp@369: for master access, for example. In this case, the module has to
fp@369: provide the locking mechanism, because it depends on the module's
fp@369: architecture which lock has to be used. The module makes this locking
fp@369: mechanism available to the master through the master's locking
fp@369: callbacks.
fp@369: 
fp@369: In case of RTAI, the lock can be an RTAI semaphore, as shown in
fp@369: listing~\ref{lst:convar}. A normal linux semaphore would not be
fp@369: appropriate, because it could not block the RTAI task due to RTAI
fp@369: running in a higher domain than the linux kernel (see~\cite{rtai}).
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI semaphore for
fp@369:     concurrent access},label={lst:convar}]
fp@369:   SEM master_sem;
fp@369: \end{lstlisting}
fp@369: 
fp@369: The module has to implement the two callbacks for requesting and
fp@369: releasing the master lock. An exemplary coding can be seen in
fp@369: listing~\ref{lst:conlock}.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI locking
fp@369:     callbacks for concurrent access},label={lst:conlock}]
fp@369:   int request_lock(void *data)
fp@369:   {
fp@369:           rt_sem_wait(&master_sem);
fp@369:           return 0;
fp@369:   }
fp@369: 
fp@369:   void release_lock(void *data)
fp@369:   {
fp@369:           rt_sem_signal(&master_sem);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 1}] The \textit{request\_lock()}
fp@369:   function has a data parameter. The master always passes the value,
fp@369:   that was specified when registering the callback function. This can
fp@369:   be used for handing the master pointer. Notice, that it has an
fp@369:   integer return value (see line 4).
fp@369: \item[\normalfont\textcircled{\tiny 3}] The call to
fp@369:   \textit{rt\_sem\_wait()} either returns at once, when the semaphore
fp@369:   was free, or blocks until the semaphore is freed again. In any case,
fp@369:   the semaphore finally is reserved for the process calling the
fp@369:   request function.
fp@369: \item[\normalfont\textcircled{\tiny 4}] When the lock was requested
fp@369:   successfully, the function should return 0. The module can prohibit
fp@369:   requesting the lock by returning non-zero (see paragraph ``Tuning
fp@369:   the jitter'' below).
fp@369: \item[\normalfont\textcircled{\tiny 7}] The \textit{release\_lock()}
fp@369:   function gets the same argument passed, but has a void return value,
fp@369:   because is always succeeds.
fp@369: \item[\normalfont\textcircled{\tiny 9}] The \textit{rt\_sem\_signal()}
fp@369:   function frees the semaphore, that was prior reserved with
fp@369:   \textit{rt\_sem\_wait()}.
fp@369: \end{description}
fp@369: 
fp@369: In the module's init function, the semaphore must be initialized, and
fp@369: the callbacks must be passed to the EtherCAT master:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Module init
fp@369:     function for concurrent access},label={lst:coninit}]
fp@369:   int __init init_mod(void)
fp@369:   {
fp@369:           RTIME tick_period, requested_ticks, now;
fp@369: 
fp@369:           rt_sem_init(&master_sem, 1);
fp@369: 
fp@369:           if (!(master = ecrt_request_master(0))) {
fp@369:                   goto out_return;
fp@369:           }
fp@369: 
fp@369:           ecrt_master_callbacks(master, request_lock,
fp@369:                                 release_lock, NULL);
fp@369:           // ...
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 5}] The call to
fp@369:   \textit{rt\_sem\_init()} initializes the semaphore and sets its
fp@369:   value to 1, meaning that only one process can reserve the semaphore
fp@369:   without blocking.
fp@369: \item[\normalfont\textcircled{\tiny 11}] The callbacks are passed to
fp@369:   the master with a call to \textit{ecrt\_master\_callbacks()}. The
fp@369:   last parameter is the argument, that the master should pass with
fp@369:   each call to a callback function. Here it is not used and set to
fp@369:   \textit{NULL}.
fp@369: \end{description}
fp@369: 
fp@369: For the cyclic function being only one competitor for master access,
fp@369: it has to request the lock like any other process. There is no need to
fp@369: use the callbacks (which are meant for processes of lower priority),
fp@369: so it can access the semaphore directly:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI cyclic
fp@369:     function for concurrent access},label={lst:conrun}]
fp@369:   void run(long data)
fp@369:   {
fp@369:           while (1) {
fp@369:                   rt_sem_wait(&master_sem);
fp@369: 
fp@369:                   ecrt_master_receive(master);
fp@369:                   ecrt_domain_process(domain1);
fp@369: 
fp@369:                   k_pos = EC_READ_U32(r_ssi_input);
fp@369: 
fp@369:                   ecrt_master_run(master);
fp@369:                   ecrt_master_send(master);
fp@369: 
fp@369:                   rt_sem_signal(&master_sem);
fp@369:                   rt_task_wait_period();
fp@369:           }
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 4}] Every access to the master has
fp@369:   to be preceeded by a call to \textit{rt\_sem\_wait()}, because
fp@369:   another instance might currently access the master.
fp@369: \item[\normalfont\textcircled{\tiny 14}] When cyclic processing
fp@369:   finished, the semaphore has to be freed again, so that other
fp@369:   processes have the possibility to access the master.
fp@369: \end{description}
fp@369: 
fp@369: A little change has to be made to the cleanup function in case of
fp@369: concurrent master access.
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={RTAI module
fp@369:     cleanup function for concurrent access},label={lst:conclean}]
fp@369:   void __exit cleanup_mod(void)
fp@369:   {
fp@369:           rt_task_delete(&task);
fp@369:           stop_rt_timer();
fp@369:           ecrt_master_deactivate(master);
fp@369:           ecrt_release_master(master);
fp@369:           rt_sem_delete(&master_sem);
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 7}] Upon module cleanup, the
fp@369:   semaphore has to be deleted, so that memory can be freed.
fp@369: \end{description}
fp@369: 
fp@369: \paragraph{Tuning the Jitter}
fp@369: \index{Jitter}
fp@369: 
fp@369: Concurrent access leads to higher jitter of the realtime process,
fp@369: because there are situations, in which the realtime process has to
fp@369: wait for a process of lower priority to finish accessing the master.
fp@369: In most cases this is acceptable, because a master access cycle
fp@369: (receive/process/send) only takes $10$~\textmu s to $20$~\textmu s on
fp@369: recent systems, what would be the maximum additional jitter. However
fp@369: some applications demand a minimum jitter. For this reason the master
fp@369: access can be prohibited by the realtime module: If the time, another
fp@369: process wants to access the master, is to close to the beginning of
fp@369: the next realtime cycle, the module can disallow, that the lock is
fp@369: taken. In this case, the request callback has to return $1$, meaning
fp@369: that the lock has not been taken. The foreign process must abort its
fp@369: master access and try again next time.
fp@369: 
fp@369: This measure helps to significantly reducing the jitter produced by
fp@369: concurrent master access. Below are exerpts of an example coding:
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Variables for
fp@369:     jitter reduction},label={lst:redvar}]
fp@369:   #define FREQUENCY 10000 // RTAI task frequency in Hz
fp@369:   // ...
fp@369:   cycles_t t_last_cycle = 0;
fp@369:   const cycles_t t_critical = cpu_khz * 1000 / FREQUENCY
fp@369:                               - cpu_khz * 30 / 1000;
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 3}] The variable
fp@369:   \textit{t\_last\_cycle} holds the timer ticks at the beginning of
fp@369:   the last realtime cycle.
fp@369: \item[\normalfont\textcircled{\tiny 4}] \textit{t\_critical} contains
fp@369:   the number of ticks, that may have passed since the beginning of the
fp@369:   last cycle, until there is no more foreign access possible. It is
fp@369:   calculated by substracting the ticks for $30$~\textmu s from the
fp@369:   ticks for a complete cycle.
fp@369: \end{description}
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Cyclic function
fp@369:     with reduced jitter},label={lst:redrun}]
fp@369:   void run(long data)
fp@369:   {
fp@369:           while (1) {
fp@369:                   t_last_cycle = get_cycles();
fp@369:                   rt_sem_wait(&master_sem);
fp@369:                   // ...
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 4}] The ticks of the beginning of
fp@369:   the current realtime cycle are taken before reserving the semaphore.
fp@369: \end{description}
fp@369: 
fp@369: \begin{lstlisting}[language=C,numbers=left,caption={Request callback
fp@369:     for reduced jitter},label={lst:redreq}]
fp@369:   int request_lock(void *data)
fp@369:   {
fp@369:           // too close to the next RT cycle: deny access.
fp@369:           if (get_cycles() - t_last_cycle > t_critical)
fp@369:                   return -1;
fp@369: 
fp@369:           // allow access
fp@369:           rt_sem_wait(&master_sem);
fp@369:           return 0;
fp@369:   }
fp@369: \end{lstlisting}
fp@369: 
fp@369: \begin{description}
fp@369: \item[\normalfont\textcircled{\tiny 4}] If the time of request is too
fp@369:   close to the next realtime cycle (here: \textless~$30$~\textmu s
fp@369:   before the estimated beginning), the locking is denied. The
fp@369:   requesting process must abort its cycle.
fp@369: \end{description}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \begin{thebibliography}{99}
fp@369: \bibitem{etherlab} Ingenieurgemeinschaft IgH: EtherLab -- Open Source
fp@369:   Toolkit for rapid realtime code generation under Linux with
fp@369:   Simulink/RTW and EtherCAT technology. URL: http://etherlab.org,
fp@369:   July~31, 2006.
fp@369: \bibitem{dlspec} IEC 61158-4-12: Data-link Protocol Specification.
fp@369:   International Electrotechnical Comission (IEC), 2005.
fp@369: \bibitem{alspec} IEC 61158-6-12: Application Layer Protocol
fp@369:   Specification. International Electrotechnical Comission (IEC), 2005.
fp@369: \bibitem{gpl} GNU General Public License, Version 2. URL:
fp@369:   http://www.gnu.org/licenses/gpl.txt. August~9, 2006.
fp@369: \bibitem{lsb} Linux Standard Base. URL:
fp@369:   http://www.freestandards.org/en/LSB. August~9, 2006.
fp@369: \bibitem{wireshark} Wireshark. URL: http://www.wireshark.org.
fp@369:   August~9, 2006.
fp@369: \bibitem{automata} {\it Hopcroft, J.~E. / Ullman, J.~D.}: Introduction
fp@369:   to Automata Theory, Languages and Computation. Adison-Wesley,
fp@369:   Reading, Mass.~1979.
fp@369: \bibitem{fsmmis} {\it Wagner, F. / Wolstenholme, P.}: State machine
fp@369:   misunderstandings. In: IEE journal ``Computing and Control
fp@369:   Engineering'', 2004.
fp@369: \bibitem{rtai} RTAI. The RealTime Application Interface for Linux from
fp@369:   DIAPM. URL: http://www.rtai.org, 2006.
fp@369: \end{thebibliography}
fp@369: 
fp@369: \printglossary
fp@369: \addcontentsline{toc}{chapter}{\nomname}
fp@369: \markleft{\nomname}
fp@369: 
fp@369: \printindex
fp@369: \markleft{Index}
fp@369: 
fp@369: %------------------------------------------------------------------------------
fp@369: 
fp@369: \end{document}
fp@369: 
fp@369: %------------------------------------------------------------------------------