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-%------------------------------------------------------------------------------
-%
-%  IgH EtherCAT Master Documentation
-%
-%  $Id$
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-
-\documentclass[a4paper,12pt,BCOR6mm,bibtotoc,idxtotoc]{scrbook}
-
-\usepackage[latin1]{inputenc}
-\usepackage[automark,headsepline]{scrpage2}
-\usepackage{graphicx}
-\usepackage{makeidx}
-\usepackage[refpage]{nomencl}
-\usepackage{listings}
-\usepackage{svn}
-\usepackage{textcomp}
-\usepackage{url}
-\usepackage{hyperref}
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-  <5><6><7><8><9><10><10.95><12><14.4><17.28><20.74><24.88>cmttb10
-}{}
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-\lstset{basicstyle=\ttfamily\small,numberstyle=\tiny,aboveskip=4mm,
-  belowskip=2mm,gobble=2,escapechar=`}
-\renewcommand\lstlistlistingname{List of Listings}
-
-\renewcommand\nomname{Glossary}
-
-\newcommand{\IgH}{\raisebox{-0.7667ex}
-  {\includegraphics[height=2.2ex]{images/ighsign}}}
-
-\SVN $Date$
-\SVN $Revision$
-
-\makeindex
-\makeglossary
-
-%------------------------------------------------------------------------------
-
-\begin{document}
-
-\pagenumbering{roman}
-\pagestyle{empty}
-
-\begin{titlepage}
-  \begin{center}
-    \rule{\textwidth}{1.5mm}
-
-    {\Huge\bf IgH \includegraphics[height=2.4ex]{images/ethercat}
-      Master 1.1\\[1ex]
-      Documentation}
-
-    \vspace{1ex}
-    \rule{\textwidth}{1.5mm}
-
-    \vspace{\fill}
-    {\Large Florian Pose, \url{fp@igh-essen.com}\\[1ex]
-      Ingenieurgemeinschaft \IgH}
-
-    \vspace{\fill}
-    {\Large Essen, \SVNDate\\[1ex]
-      Revision \SVNRevision}
-  \end{center}
-\end{titlepage}
-
-%------------------------------------------------------------------------------
-
-\tableofcontents
-\listoftables
-\listoffigures
-\lstlistoflistings
-
-%------------------------------------------------------------------------------
-
-\newpage
-\pagestyle{scrheadings}
-
-\section*{Conventions}
-\addcontentsline{toc}{section}{Conventions}
-\markleft{Conventions}
-
-The following typographic conventions are used:
-
-\begin{itemize}
-\item \textit{Italic face} is used for newly introduced terms, file
-  names, parameter names and in-text source code elements.
-\item \texttt{Typewriter face} is used for code examples and
-  command line output.
-\item \texttt{\textbf{Bold typewriter face}} is used for user input in
-  command lines.
-\end{itemize}
-
-Data values and addresses are specified as hexadecimal values with the
-prefix 0x. Example: 0x88A4. Unless otherwise noted, address values are
-specified as byte addresses.
-
-Concerning bit operations, the phrase ``setting a bit'', stands for
-setting the bit to $1$, ``clearing a bit'' means setting it to $0$,
-respectively.
-
-Function names are always printed with parentheses, but without
-parameters. So, if a function \textit{ecrt\_request\_master()} has
-empty parentheses, this does not mean, that it has no parameters.
-
-If shell commands have to be entered, this is marked by a prompt:
-
-\begin{lstlisting}[gobble=2]
-  host>
-\end{lstlisting}
-
-Further, if a shell command has to be entered as the superuser, the
-prompt ends with a mesh:
-
-\begin{lstlisting}[gobble=2]
-  host#
-\end{lstlisting}
-
-%------------------------------------------------------------------------------
-
-\chapter{The IgH EtherCAT Master}
-\label{chapter:master}
-\pagenumbering{arabic}
-
-This section will first introduce the master's general features and
-the concepts used for master development and will then explain the
-master's general architecture and offer details of the different
-modules. In addition, it will cover state machine definitions, mailbox
-protocol implementation and the user space interface. The last section
-will deal with timing aspects.
-
-%------------------------------------------------------------------------------
-
-\section{Feature Summary}
-\label{sec:summary}
-\index{Master!Features}
-
-The list below gives a short summary of the features of the
-implemented EtherCAT master.
-
-\begin{itemize}
-\item The master runs as a kernel module for Linux 2.6.
-\item It comes with EtherCAT-capable network driver for RealTek
-  RTL8139 (and compatible) network interface cards.
-  \begin{itemize}
-  \item The Ethernet hardware is operated without interrupts.
-  \item Drivers for additional Ethernet hardware can easily be
-    implemented due to a common device interface provided by the
-    master.
-  \end{itemize}
-\item The master module supports multiple EtherCAT masters on one
-  machine.
-\item The master code supports any Linux realtime extension through
-  its independent architecture.
-  \begin{itemize}
-  \item RTAI\nomenclature{RTAI}{RealTime Application Interface},
-    ADEOS\nomenclature{ADEOS}{Adaptive Domain Environment for
-      Operating Systems}, etc.
-  \item It runs well even without realtime extensions.
-  \end{itemize}
-\item Common ``realtime interface'' for modules, that want to use
-  EtherCAT functionality.
-  \begin{itemize}
-  \item Synchronous and asynchronous sending and receiving of frames
-    is supported.
-  \item Avoidance of unnecessary copy operations for process data.
-  \end{itemize}
-\item \textit{Domains} are introduced, to allow grouping of process
-  data objects.
-  \begin{itemize}
-  \item Handling of multiple domains with different sampling rates.
-  \item Automatic calculation of process data mapping, FMMU and sync manager
-    configuration within each domain.
-  \end{itemize}
-\item Communication through serveral finite state machines.
-  \begin{itemize}
-  \item Bus monitoring possible during realtime operation.
-  \item Automatic reconfiguration of slaves on bus power failure
-    during realtime operation.
-  \item Controlling of single slaves during realtime operation.
-  \end{itemize}
-\item Master idle mode.
-  \begin{itemize}
-  \item Automatic scanning of slaves upon topology changes.
-  \item Bus visualisation and EoE processing without a realtime module
-    connected.
-  \end{itemize}
-\item Implementation of the CANopen-over-EtherCAT (CoE) protocol.
-  \begin{itemize}
-  \item Configuration of CoE-capable slaves via SDO interface.
-  \end{itemize}
-\item Implementation of the Ethernet-over-EtherCAT (EoE) protocol.
-  \begin{itemize}
-  \item Each master creates virtual network devices that are
-    automatically coupled to EoE-cap\-able slaves found.
-  \item This implementation natively supports either a switched or a
-    routed EoE network architecture.
-  \end{itemize}
-\item User space interface via the System Filesystem
-  (Sysfs)\nomenclature{Sysfs}{System Filesystem}.
-  \begin{itemize}
-  \item User space tool for bus visualisation.
-  \item Slave E$^2$PROM image reading and writing.
-  \end{itemize}
-\item Seamless system integration though LSB\nomenclature{LSB}{Linux
-    Standard Base} compliance.
-  \begin{itemize}
-  \item Master and network device configuration via Sysconfig files.
-  \item Linux Standard Base compatible init script for master control.
-  \end{itemize}
-\item Virtual read-only network interface for monitoring and debugging
-  purposes.
-\end{itemize}
-
-%------------------------------------------------------------------------------
-
-\section{License}
-\label{sec:license}
-
-The master code is released under the terms and conditions of the GNU
-General Public License\index{GPL} \cite{gpl} (version 2). Other
-developers, that want to use EtherCAT with Linux systems, are invited
-to use the master code or even participate on development.
-
-%------------------------------------------------------------------------------
-
-\section{General Master Architecture}
-\label{sec:masterarch}
-\index{Master!Architecture}
-
-The EtherCAT master is integrated into the Linux 2.6 kernel. This was
-an early design decision, which has been made for serveral reasons:
-
-\begin{itemize}
-\item Kernel code has significantly better realtime characteristics,
-  i.~e. less jitter than user space code. It was foreseeable, that a
-  fieldbus master has a lot of cyclic work to do. Cyclic work is
-  usually triggered by timer interrupts inside the kernel. The
-  execution delay of a function that processes timer interrupts is
-  less, when it resides in kernel space, because there is no need of
-  time-consuming context switches to a user space process.
-\item It was also foreseeable, that the master code has to directly
-  communicate with the Ethernet hardware. This has to be done in the
-  kernel anyway (through network device drivers), which is one more
-  reason for the master code being in kernel space.
-\end{itemize}
-
-A general overview of the master architecture can be seen in
-figure~\ref{fig:masterarch}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/masterarch}
-  \caption{Master architecture}
-  \label{fig:masterarch}
-\end{figure}
-
-\paragraph{Master Module}
-\index{Master module}
-
-The EtherCAT master mainly consists of the master module, containing
-one or more EtherCAT masters (section~\ref{sec:mastermod}), the
-``Device Interface'' (section~\ref{sec:ecdev}) and the ``Realtime
-Interface'' (section~\ref{sec:ecrt}).
-
-\paragraph{Device Modules}
-\index{Device modules}
-
-Furthermore there are EtherCAT-capable network device driver
-modules\index{Device modules}, that connect to the EtherCAT master via
-the device interface. These modified network drivers can handle both
-network devices used for EtherCAT operation and ``normal'' Ethernet
-devices. The common case is, that the master module offers a single
-EtherCAT master: An EtherCAT-capable network device driver module
-connects one network device to this master, that is now able to send
-and receive EtherCAT frames, while all other network devices handled
-by the network driver get connected to the kernel's network stack as
-usual.
-
-\paragraph{Realtime Modules}
-
-A ``realtime module''\index{Realtime module} is a kernel module, that
-uses the EtherCAT master for cyclic exchange of process data with
-EtherCAT slaves. Realtime modules are not part of the EtherCAT master
-code\footnote{Although there are serveral examples provided in the
-  \textit{examples} directory, see chapter~\ref{chapter:usage} for
-  more information}, so anybody wanting to use the master has to write
-one. A realtime module can ``request'' a master through the realtime
-interface. If this succeeds, the module has the control over the
-master. It can now configure slaves and set up a process data image
-(see section~\ref{sec:processdata}) for cyclic exchange. This cyclic
-code has to be provided by the realtime module, so it is in hands of
-the developer, which mechanism to use for this. Moreover he has to
-decide, whether or not using a Linux realtime extension.
-
-\paragraph{Why ``Realtime'' Module?}
-
-The name shall not imply, that a linux realtime extension is
-mandatory: The master runs well even without realtime extensions, as
-section~\ref{sec:mini} shows. However, the code using the master is
-time-critical, because process data IO has to be done in cyclic work.
-Some EtherCAT slaves support watchdog units, that stop driving the
-outputs when process data was not exchanged for some time. So the
-names ``realtime interface'' and ``realtime module'' are quite
-appropriate.
-
-%------------------------------------------------------------------------------
-
-\subsection{Handling of Process Data}
-\label{sec:processdata}
-
-\paragraph{Process Data Image}
-\index{Process data}
-
-The slaves offer their inputs and outputs by presenting the master
-so-called ``Process Data Objects'' (PDOs\index{PDO}). The available
-PDOs can be determined by reading out the slave's TXPDO and RXPDO
-E$^2$PROM categories. The realtime module can register the PDOs for
-data exchange during cyclic operation. The sum of all registered PDOs
-defines the ``process data image'', which is exchanged via the
-``Logical ReadWrite'' datagrams introduced
-in~\cite[section~5.4.2.4]{dlspec}.
-
-\paragraph{Process Data Domains}
-\index{Domain}
-
-The process data image can be easily managed by creating co-called
-``domains'', which group PDOs and allocate the datagrams needed to
-exchange them. Domains are mandatory for process data exchange, so
-there has to be at least one. They were introduced for the following
-reasons:
-
-\begin{itemize}
-\item The maximum size of a ``Logical ReadWrite'' datagram is limited
-  due to the limited size of an Ethernet frame: The maximum data size
-  is the Ethernet data field size minus the EtherCAT frame header,
-  EtherCAT datagram header and EtherCAT datagram footer: $1500 - 2 -
-  12 - 2 = 1484$ octets. If the size of the process data image exceeds
-  this limit, multiple frames have to be sent, and the image has to be
-  partitioned for the use of multiple datagrams. A domain manages this
-  automatically.
-\item Not every PDO has to be exchanged with the same frequency: The
-  values of PDOs can vary slowly over time (for example temperature
-  values), so exchanging them with a high frequency would just waste
-  bus bandwidth. For this reason, multiple domains can be created, to
-  group different PDOs and so allow separate exchange.
-\end{itemize}
-
-There is no upper limit for the number of domains, but each domain
-occupies one FMMU in each slave involved, so the maximum number of
-domains is also limited by the slaves' capabilities.
-
-\paragraph{FMMU Configuration}
-\index{FMMU!Configuration}
-
-A realtime module can register PDOs for process data exchange. Every
-PDO is part of a memory area in the slave's physical memory, that is
-protected by a sync manager \cite[section~6.7]{dlspec} for
-synchronized access. In order to make a sync manager react on a
-datagram accessing its memory, it is necessary to access the last byte
-covered by the sync manager. Otherwise the sync manager will not react
-on the datagram and no data will be exchanged. That is why the whole
-synchronized memory area has to be included into the process data
-image: For example, if a certain PDO of a slave is registered for
-exchange with a certain domain, one FMMU will be configured to map the
-complete sync-manager-protected memory, the PDO resides in. If a
-second PDO of the same slave is registered for process data exchange
-within the same domain, and this PDO resides in the same
-sync-manager-protected memory as the first PDO, the FMMU configuration
-is not touched, because the appropriate memory is already part of the
-domain's process data image.  If the second PDO belongs to another
-sync-manager-protected area, this complete area is also included into
-the domains process data image. See figure~\ref{fig:fmmus} for an
-overview, how FMMU's are configured to map physical memory to logical
-process data images.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=\textwidth]{images/fmmus}
-  \caption{FMMU configuration for serveral domains}
-  \label{fig:fmmus}
-\end{figure}
-
-\paragraph{Process Data Pointers}
-
-The figure also demonstrates the way, the realtime module can access the
-exchanged process data: At PDO registration, the realtime module has
-to provide the address of a process data pointer. Upon calculation of
-the domain image and allocation of process data memory, this pointer
-is redirected to the appropriate location inside the domain's process
-data memory and can later be easily dereferenced by the module code.
-
-%------------------------------------------------------------------------------
-
-\subsection{Operation Modes}
-\index{Master modes}
-
-The EtherCAT master has serveral modes of operation:
-
-\begin{description}
-\item[Orphaned Mode] This mode takes effect, when the master has no
-  EtherCAT-capable network device connected. No bus communication is
-  possible, so this mode is not of further interest.
-\item[Idle Mode]\index{Idle mode} takes effect when the master is
-  unused (i.~e. there is no realtime module, that reserved the
-  master). In this case, the master has the ability to scan the bus by
-  itsself and generously allow bus access from user space.  This mode
-  is meant for maintenance and visualisation.
-\item[Operation Mode]\index{Operation mode} The master is reserved for
-  exclusive access by a realtime module. In this mode, the master is
-  adjusted for availability and monitoring. Access from user space is
-  very restrictive and mostly limited to reading direction.
-
-\end{description}
-
-Figure~\ref{fig:modes} shows the three modes and the possible mode
-transitions.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/modes}
-  \caption{Master modes and transitions}
-  \label{fig:modes}
-\end{figure}
-
-\subsubsection{Idle Mode}
-\index{Idle mode}
-
-The master enters idle mode upon connection of a device module (see
-section~\ref{sec:device}) or releasing by a realtime module. The
-master owns a kernel workqueue and a suitable work structure, which is
-used to cyclically process the ``Idle state machine'' (see
-section~\ref{sec:fsm-idle}). This state machine automatically scans
-the bus for slaves (and re-scans upon topology changes), configures
-slaves for idle operation and executes pending operations from the
-user space interface (for example E$^2$PROM writing). On device
-disconnection or realtime request, the idle mode is stopped by
-cancelling the work and flushing the workqueue.
-
-\subsubsection{Operation Mode}
-\index{Operation mode}
-
-Operation mode is entered when a realtime module requests the master.
-The idle mode is stopped and the bus is scanned by getting the number
-of slaves and executing the ``Slave scan state machine'' (see
-section~\ref{sec:fsm-scan}) for each slave. The master is now ready to
-create domains and accept PDO registrations and slave configurations.
-After that, cyclic communication can be done by the realtime module.
-
-\paragraph{Master Phases}
-
-Every realtime module should use the master in three phases:
-
-\begin{enumerate}
-\item \textit{Startup} - The master is requested and the bus is
-  validated. Domains are created and PDOs are registered. Slave
-  configurations are applied.
-\item \textit{Operation} - Cyclic code is run, process data is
-  exchanged and the master state machine is executed.
-\item \textit{Shutdown} - Cyclic code is stopped and the master
-  is released.
-\end{enumerate}
-
-%------------------------------------------------------------------------------
-
-\section{Device Modules}
-\label{sec:device}
-\index{Device modules}
-
-Device modules are network device driver modules that handle Ethernet
-devices, which the master can use to connect to an EtherCAT bus.
-
-Section~\ref{sec:networkdrivers} offers an overview of general Linux
-network driver modules, while section~\ref{sec:requirements} will show
-the requirements to an EtherCAT-enabled network driver. Finally,
-sections~\ref{sec:seldev} to~\ref{sec:patching} show how to fulfill
-these requirements and implement such a driver module.
-
-%------------------------------------------------------------------------------
-
-\subsection{Network Driver Basics}
-\label{sec:networkdrivers}
-\index{Network drivers}
-
-EtherCAT relies on Ethernet hardware and the master needs a physical
-Ethernet device to communicate with the bus. Therefore it is necessary
-to understand how Linux handles network devices and their drivers,
-respectively.
-
-\paragraph{Tasks of a Network Driver}
-
-Network device drivers handle the lower two layers of the OSI model,
-that is the physical layer and the data-link layer. A network device
-itself natively handles the physical layer issues: It represents the
-hardware to connect to the medium and to send and receive data in the
-way, the physical layer protocol describes. The network device driver
-is responsible for getting data from the kernel's networking stack and
-forwarding it to the hardware, that does the physical transmission.
-If data is received by the hardware respectively, the driver is
-notified (usually by means of an interrupt) and has to read the data
-from the hardware memory and forward it to the network stack. There
-are a few more tasks, a network device driver has to handle, including
-queue control, statistics and device dependent features.
-
-\paragraph{Driver Startup}
-
-Usually, a driver searches for compatible devices on module loading.
-For PCI drivers, this is done by scanning the PCI bus and checking for
-known device IDs. If a device is found, data structures are allocated
-and the device is taken into operation.
-
-\paragraph{Interrupt Operation}
-\index{Interrupt}
-
-A network device usually provides a hardware interrupt that is used to
-notify the driver of received frames and success of transmittion, or
-errors, respectively. The driver has to register an interrupt service
-routine (ISR\index{ISR}\nomenclature{ISR}{Interrupt Service Routine}),
-that is executed each time, the hardware signals such an event. If the
-interrupt was thrown by the own device (multiple devices can share one
-hardware interrupt), the reason for the interrupt has to be determined
-by reading the device's interrupt register. For example, if the flag
-for received frames is set, frame data has to be copied from hardware
-to kernel memory and passed to the network stack.
-
-\paragraph{The net\_device structure}
-\index{net\_device}
-
-The driver registers a \textit{net\_device} structure for each device
-to communicate with the network stack and to create a ``network
-interface''. In case of an Ethernet driver, this interface appears as
-\textit{ethX}, where X is a number assigned by the kernel on
-registration. The \textit{net\_device} structure receives events
-(either from user space or from the network stack) via serveral
-callbacks, which have to be set before registration. Not every
-callback is mandatory, but for reasonable operation the ones below are
-needed in any case:
-
-\begin{description}
-\item[int (*open)(struct net\_device *)] This function is called when
-  network communication has to be started, for example after a command
-  \textit{ifconfig ethX up} from user space. Frame reception has to be
-  enabled by the driver.
-\item[int (*stop)(struct net\_device *)] The purpose of this callback
-  is to ``close'' the device, i.~e. make the hardware stop receiving
-  frames.
-\item[int (*hard\_start\_xmit)(struct sk\_buff *, struct net\_device
-  *)] This function is cal\-led for each frame that has to be
-  transmitted.  The network stack passes the frame as a pointer to an
-  \textit{sk\_buff} structure (``socket buffer''\index{Socket buffer},
-  see below), which has to be freed after sending.
-\item[struct net\_device\_stats *(*get\_stats)(struct net\_device *)]
-  This call has to return a pointer to the device's
-  \textit{net\_device\_stats} structure, which permanently has to be
-  filled with frame statistics. This means, that everytime a frame is
-  received, sent, or an error happened, the appropriate counter in
-  this structure has to be increased.
-\end{description}
-
-The actual registration is done with the \textit{register\_netdev()}
-call, unregistering is done with \textit{unregister\_netdev()}.
-
-\paragraph{The netif Interface}
-\index{netif}
-
-All other communication in the direction interface $\to$ network stack
-is done via the \textit{netif\_*} calls. For example, on successful
-device opening, the network stack has to be notified, that it can now
-pass frames to the interface. This is done by calling
-\textit{netif\_start\_queue()}. After this call, the
-\textit{hard\_start\_xmit()} callback can be called by the network
-stack. Furthermore a network driver usually manages a frame
-transmission queue. If this gets filled up, the network stack has to
-be told to stop passing further frames for a while. This happens with
-a call to \textit{netif\_stop\_queue()}. If some frames have been
-sent, and there is enough space again to queue new frames, this can be
-notified with \textit{netif\_wake\_queue()}. Another important call is
-\textit{netif\_receive\_skb()}\footnote{This function is part of the
-  NAPI (``New API''), that replaces the ``old'' kernel 2.4 technique
-  for interfacing to the network stack (with \textit{netif\_rx()}).
-  NAPI is a technique to improve network performance on Linux. Read
-  more in
-  http://www.cyberus.ca/\textasciitilde{}hadi/usenix-paper.tgz}: It
-passes a frame to the network stack, that was just received by the
-device.  Frame data has to be packed into a so-called ``socket
-buffer'' for that (see below).
-
-\paragraph{Socket Buffers}
-\index{Socket buffer}
-
-Socket buffers are the basic data type for the whole network stack.
-They serve as containers for network data and are able to quickly add
-data headers and footers, or strip them off again. Therefore a socket
-buffer consists of an allocated buffer and serveral pointers that mark
-beginning of the buffer (\textit{head}), beginning of data
-(\textit{data}), end of data (\textit{tail}) and end of buffer
-(\textit{end}). In addition, a socket buffer holds network header
-information and (in case of received data) a pointer to the
-\textit{net\_device}, it was received on. There exist functions that
-create a socket buffer (\textit{dev\_alloc\_skb()}), add data either
-from front (\textit{skb\_push()}) or back (\textit{skb\_put()}),
-remove data from front (\textit{skb\_pull()}) or back
-(\textit{skb\_trim()}), or delete the buffer (\textit{kfree\_skb()}).
-A socket buffer is passed from layer to layer, and is freed by the
-layer that uses it the last time. In case of sending, freeing has to
-be done by the network driver.
-
-%------------------------------------------------------------------------------
-
-\subsection{EtherCAT Network Drivers}
-\label{sec:requirements}
-
-There are a few requirements for Ethernet network devices to function
-as EtherCAT devices, when connected to an EtherCAT bus.
-
-\paragraph{Dedicated Interfaces}
-
-For performance and realtime purposes, the EtherCAT master needs
-direct and exclusive access to the Ethernet hardware. This implies
-that the network device must not be connected to the kernel's network
-stack as usual, because the kernel would try to use it as an ordinary
-Ethernet device.
-
-\paragraph{Interrupt-less Operation}
-\index{Interrupt}
-
-EtherCAT frames travel through the logical EtherCAT ring and are then
-sent back to the master. Communication is highly deterministic: A
-frame is sent and will be received again after a constant time.
-Therefore, there is no need to notify the driver about frame
-reception: The master can instead query the hardware for received
-frames.
-
-Figure~\ref{fig:interrupt} shows two workflows for cyclic frame
-transmittion and reception with and without interrupts.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.8\textwidth]{images/interrupt}
-  \caption{Interrupt Operation versus Interrupt-less Operation}
-  \label{fig:interrupt}
-\end{figure}
-
-In the left workflow ``Interrupt Operation'', the data from the last
-cycle is first processed and a new frame is assembled with new
-datagrams, which is then sent.  The cyclic work is done for now.
-Later, when the frame is received again by the hardware, an interrupt
-is triggered and the ISR is executed. The ISR will fetch the frame
-data from the hardware and initiate the frame dissection: The
-datagrams will be processed, so that the data is ready for processing
-in the next cycle.
-
-In the right workflow ``Interrupt-less Operation'', there is no
-hardware interrupt enabled.  Instead, the hardware will be polled by
-the master by executing the ISR. If the frame has been received in the
-meantime, it will be dissected. The situation is now the same as at
-the beginning of the left workflow: The received data is processed and
-a new frame is assembled and sent. There is nothing to do for the rest
-of the cycle.
-
-The interrupt-less operation is desirable, because there is simply no
-need for an interrupt. Moreover hardware interrupts are not conducive
-in improving the driver's realtime behaviour: Their undeterministic
-incidences contribute to increasing the jitter. Besides, if a realtime
-extension (like RTAI) is used, some additional effort would have to be
-made to priorize interrupts.
-
-\paragraph{Ethernet and EtherCAT Devices}
-
-Another issue lies in the way Linux handles devices of the same type.
-For example, a PCI\nomenclature{PCI}{Peripheral Component
-  Interconnect, Computer Bus} driver scans the PCI bus for devices it
-can handle. Then it registers itself as the responsible driver for all
-of the devices found. The problem is, that an unmodified driver can
-not be told to ignore a device because it will be used for EtherCAT
-later. There must be a way to handle multiple devices of the same
-type, where one is reserved for EtherCAT, while the other is treated
-as an ordinary Ethernet device.
-
-For all this reasons, the author has decided that the only acceptable
-solution is to modify standard Ethernet drivers in a way that they
-keep their normal functionality, but gain the ability to treat one or
-more of the devices as EtherCAT-capable.
-
-Below are the advantages of this solution:
-
-\begin{itemize}
-\item No need to tell the standard drivers to ignore certain devices.
-\item One networking driver for EtherCAT and non-EtherCAT devices.
-\item No need to implement a network driver from scratch and running
-  into issues, the former developers already solved.
-\end{itemize}
-
-The chosen approach has the following disadvantages:
-
-\begin{itemize}
-\item The modified driver gets more complicated, as it must handle
-  EtherCAT and non-EtherCAT devices.
-\item Many additional case differentiations in the driver code.
-\item Changes and bugfixes on the standard drivers have to be ported
-  to the Ether\-CAT-capable versions from time to time.
-\end{itemize}
-
-%------------------------------------------------------------------------------
-
-\subsection{Device Selection}
-\label{sec:seldev}
-
-After loading the master module, at least one EtherCAT-capable network
-driver module has to be loaded, that connects one of its devices to
-the master. To specify an EtherCAT device and the master to connect
-to, all EtherCAT-capable network driver modules should provide two
-module parameters:
-
-\begin{description}
-\item[ec\_device\_index] PCI device index of the device that is
-  connected to the EtherCAT bus. If this parameter is left away, all
-  devices found are treated as ordinary Ethernet devices. Default:
-  $-1$
-\item[ec\_master\_index] Index of the master to connect to. Default:
-  $0$
-\end{description}
-
-The following command loads the EtherCAT-capable RTL8139 device
-driver, telling it to handle the second device as an EtherCAT device
-and connecting it to the first master:
-
-\begin{lstlisting}
-  host# `\textbf{modprobe ec\_8139too ec\_device\_index=1}`
-\end{lstlisting}
-
-Usually, this command does not have to be entered manually, but is
-called by the EtherCAT init script. See section~\ref{sec:init} for
-more information.
-
-%------------------------------------------------------------------------------
-
-\subsection{The Device Interface}
-\label{sec:ecdev}
-\index{Device interface}
-
-An anticipation to the section about the master module
-(section~\ref{sec:mastermod}) has to be made in order to understand
-the way, a network device driver module can connect a device to a
-specific EtherCAT master.
-
-The master module provides a ``device interface'' for network device
-drivers. To use this interface, a network device driver module must
-include the header
-\textit{devices/ecdev.h}\nomenclature{ecdev}{EtherCAT Device}, coming
-with the EtherCAT master code. This header offers a function interface
-for EtherCAT devices which is explained below. All functions of the
-device interface are named with the prefix \textit{ecdev}.
-
-\paragraph{Device Registration}
-
-A network device driver can connect a physical device to an EtherCAT
-master with the \textit{ecdev\_register()} function.
-
-\begin{lstlisting}[language=C]
-  ec_device_t *ecdev_register(unsigned int master_index,
-                              struct net_device *net_dev,
-                              ec_isr_t isr,
-                              struct module *module);
-\end{lstlisting}
-
-The first parameter \textit{master\_index} must be the index of the
-EtherCAT master to connect to (see section~\ref{sec:mastermod}),
-followed by \textit{net\_dev}, the pointer to the corresponding
-net\_device structure, which represents the network device to connect.
-The third parameter \textit{isr} must be a pointer to the interrupt
-service routine (ISR\index{ISR}) handling the device. The master will
-later execute the ISR in order to receive frames and to update the
-device status. The last parameter \textit{module} must be the pointer
-to the device driver module, which is usually accessible via the macro
-\textit{THIS\_MODULE} (see next paragraph). On success, the function
-returns a pointer to an \textit{ec\_device\_t} object, which has to be
-specified when calling further functions of the device interface.
-Therefore the device module has to store this pointer for future use.
-In error case, the \textit{ecdev\_register()} returns \textit{NULL},
-which means that the device could not be registered.  The reason for
-this is printed to \textit{syslog}\index{syslog}. In this case, the
-device module is supposed to abort the module initialisation and let
-the \textit{insmod} command fail.
-
-\paragraph{Implicit Dependencies}
-
-The reason for the module pointer has to be specified at device
-registration is a non-trivial one: The master has to know about the
-module, because there will be an implicit dependency between the
-device module and a later connected realtime module: When a realtime
-module connects to the master, the use count of the master module will
-be increased, so that the master module can not be unloaded for the
-time of the connection. This is reasonable, and so automatically done
-by the kernel. The kernel knows about this dependency, because the
-realtime module uses kernel symbols provided by the master module.
-Moreover it is mandatory, that the device module can be unloaded
-neither, because it is implicitely used by the realtime module, too.
-Unloading it would lead to a fatal situation, because the master would
-have no device to send and receive frames for the realtime module.
-This dependency can not be detected automatically, because the
-realtime module does not use any symbols of the device module.
-Therefore the master explicitly increments the use counter of the
-connected device module upon connection of a realtime module and
-decrements it, if the realtime module disconnects. In this manner, it
-is impossible to unload a device module while the master is in use.
-This is done with the kernel function pair \textit{try\_module\_get()}
-\index{try\_module\_get@\textit{try\_module\_get()}} and
-\textit{module\_put()} \index{module\_put@\textit{module\_put()}}. The
-first one increases the use count of a module and only fails, if the
-module is currenly being unloaded. The last one decreases the use
-count again and never fails. Both functions take a pointer to the
-module as their argument, which the device module therefore has to
-specify upon device registration.
-
-\paragraph{Device Unregistering}
-
-The unregistration of a device is usually done in the device module's
-cleanup function, by calling the \textit{ecdev\_unregister()} function
-and specifying the master index and a pointer to the device object
-again.
-
-\begin{lstlisting}[language=C]
-  void ecdev_unregister(unsigned int master_index,
-                        ec_device_t *device);
-\end{lstlisting}
-
-This function can fail too (if the master index is invalid, or the
-given device was not registered), but due to the fact, that this
-failure can not be dealt with appropriately, because the device module
-is unloading anyway, the failure code would not be of any interest. So
-the function has a void return value.
-
-\paragraph{Starting the Master}
-
-When a device has been initialized completely and is ready to send and
-receive frames, the master has to be notified about this by calling
-the \textit{ecdev\_start()} function.
-
-\begin{lstlisting}[language=C]
-  int ecdev_start(unsigned int master_index);
-\end{lstlisting}
-
-The master will then enter ``Idle Mode'' and start scanning the bus
-(and possibly handling EoE slaves). Moreover it will make the bus
-accessible via Sysfs interface and react to user interactions. The
-function takes one parameter \textit{master\_index}, which has to be
-the same as at the call to \textit{ecdev\_register()}. The return
-value will be non-zero if the starting process failed. In this case
-the device module is supposed to abort the init sequence and make the
-init function return an error code.
-
-\paragraph{Stopping the Master}
-
-Before a device can be unregistered, the master has to be stopped by
-calling the \textit{ecdev\_stop()} function. It will stop processing
-messages of EoE slaves and leave ``Idle Mode''. The only parameter is
-\textit{master\_index}. This function can not fail.
-
-\begin{lstlisting}[language=C]
-  void ecdev_stop(unsigned int master_index);
-\end{lstlisting}
-
-A subsequent call to \textit{ecdev\_unregister()} will now unregister
-the device savely.
-
-\paragraph{Receiving Frames}
-
-The interrupt service routine handling device events usually has a
-section where new frames are fetched from the hardware and forwarded
-to the kernel network stack via \textit{netif\_receive\_skb()}. For an
-EtherCAT-capable device, this has to be replaced by calling the
-\textit{ecdev\_receive()} function to forward the received data to the
-connected EtherCAT master instead.
-
-\begin{lstlisting}[language=C]
-  void ecdev_receive(ec_device_t *device,
-                     const void *data,
-                     size_t size);
-\end{lstlisting}
-
-This function takes 3 arguments, a pointer to the device object
-(\textit{device}), a pointer to the received data, and the size of the
-received data. The data range has to include the Ethernet headers
-starting with the destination address and reach up to the last octet
-of EtherCAT data, excluding the FCS. Most network devices handle the
-FCS in hardware, so it is not seen by the driver code and therefore
-doesn't have to be cut off manually.
-
-\paragraph{Handling the Link Status}
-
-Information about the link status (i.~e. if there is a carrier signal
-detected on the physical port) is also important to the master. This
-information is usually gathered by the ISR and should be forwarded to
-the master by calling the \textit{ecdev\_link\_state()} function. The
-master then can react on this and warn the realtime module of a lost
-link.
-
-\begin{lstlisting}[language=C]
-  void ecdev_link_state(ec_device_t *device,
-                        uint8_t new_state);
-\end{lstlisting}
-
-The parameter \textit{device} has to be a pointer to the device object
-returned by \textit{ecdev\_\-register()}. With the second parameter
-\textit{new\_state}, the new link state is passed: 1, if the link went
-up, and 0, if it went down.
-
-%------------------------------------------------------------------------------
-
-\subsection{Patching Network Drivers}
-\label{sec:patching}
-\index{Network drivers}
-
-This section will demonstrate, how to make a standard Ethernet driver
-EtherCAT-capable. The below code examples are taken out of the
-modified RealTek RTL8139 driver coming with the EtherCAT master
-(\textit{devices/8139too.c}). The driver was originally developed by
-Donald Becker, and is currently maintained by Jeff Garzik.
-
-Unfortunately, there is no standard procedure to enable an Ethernet
-driver for use with the EtherCAT master, but there are a few common
-techniques, that are described in this section.
-
-\begin{enumerate}
-\item A first simple rule is, that \textit{netif\_*()}-calls must be
-  strictly avoided for all EtherCAT devices. As mentioned before,
-  EtherCAT devices have no connection to the network stack, and
-  therefore must not call its interface functions.
-\item Another important thing is, that EtherCAT devices should be
-  operated without interrupts. So any calls of registering interrupt
-  handlers and enabling interrupts at hardware level must be avoided,
-  too.
-\item The master does not use a new socket buffer for each send
-  operation: Instead there is a fix one allocated on master
-  initialization. This socket buffer is filled with an EtherCAT frame
-  with every send operation and passed to the
-  \textit{hard\_start\_xmit()} callback. For that it is necessary,
-  that the socket buffer is not be freed by the network driver as
-  usual.
-\end{enumerate}
-
-As mentioned before, the driver will handle both EtherCAT and ordinary
-Ethernet devices. This implies, that for each device-dependent
-operation, it has to be checked if an EtherCAT device is involved, or
-just an Ethernet device. For means of simplicity, this example driver
-will only handle one EtherCAT device. This makes the case
-differentiations easier.
-
-\paragraph{Global Variables}
-
-First of all, there have to be additional global variables declared,
-as shown in the listing:
-
-\begin{lstlisting}[language=C,numbers=left]
-  static int ec_device_index = -1;
-  static int ec_device_master_index = 0;
-  static ec_device_t *rtl_ec_dev;
-  struct net_device *rtl_ec_net_dev = NULL;
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1} -- \textcircled{\tiny 2}] To
-  comply to the requirements for parameters of EtherCAT device modules
-  described in section~\ref{sec:seldev}, there have to be additional
-  parameter variables: \textit{ec\_\-device\_\-index} holds the index
-  of the EtherCAT device and defaults to $-1$ (no EtherCAT device),
-  while \textit{ec\_device\_master\_index} stores index of the master,
-  the single device will be connected to. Default: $0$
-\item[\normalfont\textcircled{\tiny 3}] \textit{rtl\_ec\_dev} will be
-  the pointer to the later registered RealTek EtherCAT device, which
-  can be used as a parameter for device methods.
-\item[\normalfont\textcircled{\tiny 4}] \textit{rtl\_ec\_net\_dev} is
-  a pointer to the \textit{net\_device} structure of the dedicated
-  device and is set while scanning the PCI bus and finding the device
-  with the specified index. This is done inside the
-  \textit{pci\_module\_init()} function executed as the first thing on
-  module loading.
-\end{description}
-
-\paragraph{Module Initialization}
-
-Below is the (shortened) coding of the device driver's module init
-function:
-
-\begin{lstlisting}[language=C,numbers=left]
-  static int __init rtl8139_init_module(void)
-  {
-          if (pci_module_init(&rtl8139_pci_driver) < 0) {
-                  printk(KERN_ERR "Failed to init PCI mod.\n");
-                  goto out_return;
-          }
-
-          if (rtl_ec_net_dev) {
-                  printk(KERN_INFO "Registering"
-                         " EtherCAT device...\n");
-                  if (!(rtl_ec_dev =
-                          ecdev_register(ec_device_master_index,
-                                         rtl_ec_net_dev,
-                                         rtl8139_interrupt,
-                                         THIS_MODULE))) {
-                          printk(KERN_ERR "Failed to reg."
-                                          " EtherCAT device!\n");
-                          goto out_unreg_pci;
-                  }
-
-                  printk(KERN_INFO "Starting EtherCAT"
-                         " device...\n");
-                  if (ecdev_start(ec_device_master_index)) {
-                          printk(KERN_ERR "Failed to start"
-                                 " EtherCAT device!\n");
-                          goto out_unreg_ec;
-                  }
-          } else {
-                  printk(KERN_WARNING "No EtherCAT device"
-                         " registered!\n");
-          }
-
-          return 0;
-
-      out_unreg_ec:
-          ecdev_unregister(ec_device_master_index, rtl_ec_dev);
-      out_unreg_pci:
-          pci_unregister_driver(&rtl8139_pci_driver);
-      out_return:
-          return -1;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] This call initializes all
-  RTL8139-compatible devices found on the pci bus. If a device with
-  index \textit{ec\_device\_index} is found, a pointer to its
-  \textit{net\_device} structure is stored in
-  \textit{rtl\_ec\_net\_dev} for later use (see next listings).
-\item[\normalfont\textcircled{\tiny 8}] If the specified device was
-  found, \textit{rtl\_ec\_net\_dev} is non-zero.
-\item[\normalfont\textcircled{\tiny 11}] The device is connected to
-  the specified master with a call to \textit{ecdev\_register()}. If
-  this fails, module loading is aborted.
-\item[\normalfont\textcircled{\tiny 23}] The device registration was
-  successful and the master is started. This can fail, which aborts
-  module loading.
-\item[\normalfont\textcircled{\tiny 29}] If no EtherCAT device was
-  found, a warning is output.
-\end{description}
-
-\paragraph{Device Searching}
-
-During the PCI initialization phase, a variable \textit{board\_idx} is
-increased for each RTL8139-compatible device found. The code below is
-executed for each device:
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (board_idx == ec_device_index) {
-          rtl_ec_net_dev = dev;
-          strcpy(dev->name, "ec0");
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1}] The device with the specified
-  index will be the EtherCAT device.
-\end{description}
-
-\paragraph{Avoiding Device Registration}
-
-Later in the PCI initialization phase, the net\_devices get
-registered. This has to be avoided for EtherCAT devices and so this is
-a typical example for an EtherCAT case differentiation:
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (dev != rtl_ec_net_dev) {
-          i = register_netdev(dev);
-          if (i) goto err_out;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1}] If the current net\_device is
-  not the EtherCAT device, it is registered at the network stack.
-\end{description}
-
-\paragraph{Avoiding Interrupt Registration}
-
-In the next two listings, there is an interrupt requested and the
-device's interrupts are enabled. This also has to be encapsulated by
-if-clauses, because interrupt operation is not wanted for EtherCAT
-devices.
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (dev != rtl_ec_net_dev) {
-          retval = request_irq(dev->irq, rtl8139_interrupt,
-                               SA_SHIRQ, dev->name, dev);
-          if (retval) return retval;
-  }
-\end{lstlisting}
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (dev != rtl_ec_net_dev) {
-          /* Enable all known interrupts by setting
-             the interrupt mask. */
-          RTL_W16(IntrMask, rtl8139_intr_mask);
-  }
-\end{lstlisting}
-
-\paragraph{Frame Sending}
-
-The listing below shows an exerpt of the function representing the
-\textit{hard\_start\_xmit()} callback of the net\_device.
-
-\begin{lstlisting}[language=C,numbers=left]
-  /* Note: the chip doesn't have auto-pad! */
-  if (likely(len < TX_BUF_SIZE)) {
-          if (len < ETH_ZLEN)
-                  memset(tp->tx_buf[entry], 0, ETH_ZLEN);
-          skb_copy_and_csum_dev(skb, tp->tx_buf[entry]);
-          if (dev != rtl_ec_net_dev) {
-                  dev_kfree_skb(skb);
-          }
-  } else {
-          if (dev != rtl_ec_net_dev) {
-                  dev_kfree_skb(skb);
-          }
-          tp->stats.tx_dropped++;
-          return 0;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 6} + \textcircled{\tiny 10}] The
-  master uses a fixed socket buffer for transmission, which is reused
-  and may not be freed.
-\end{description}
-
-\paragraph{Frame Receiving}
-
-During ordinary frame reception, a socket buffer is created and filled
-with the received data. This is not necessary for an EtherCAT device:
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (dev != rtl_ec_net_dev) {
-          /* Malloc up new buffer, compatible with net-2e. */
-          /* Omit the four octet CRC from the length. */
-
-          skb = dev_alloc_skb (pkt_size + 2);
-          if (likely(skb)) {
-                  skb->dev = dev;
-                  skb_reserve(skb, 2); /* 16 byte align
-                                          the IP fields. */
-                  eth_copy_and_sum(skb, &rx_ring[ring_off + 4],
-                                   pkt_size, 0);
-                  skb_put(skb, pkt_size);
-                  skb->protocol = eth_type_trans(skb, dev);
-
-                  dev->last_rx = jiffies;
-                  tp->stats.rx_bytes += pkt_size;
-                  tp->stats.rx_packets++;
-
-                  netif_receive_skb (skb);
-          } else {
-                  if (net_ratelimit())
-                          printk(KERN_WARNING
-                                 "%s: Memory squeeze, dropping"
-                                 " packet.\n", dev->name);
-                  tp->stats.rx_dropped++;
-          }
-  } else {
-          ecdev_receive(rtl_ec_dev,
-                        &rx_ring[ring_offset + 4], pkt_size);
-          dev->last_rx = jiffies;
-          tp->stats.rx_bytes += pkt_size;
-          tp->stats.rx_packets++;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 28}] If the device is an EtherCAT
-  device, no socket buffer is allocated. Instead a pointer to the data
-  (which is still in the device's receive ring) is passed to the
-  EtherCAT master. Unnecessary copy operations are avoided.
-\item[\normalfont\textcircled{\tiny 30} -- \textcircled{\tiny 32}] The
-  device's statistics are updated as usual.
-\end{description}
-
-\paragraph{Link State}
-
-The link state (i.~e. if there is a carrier signal detected on the
-receive port) is determined during execution of the ISR. The listing
-below shows the different processing for Ethernet and EtherCAT
-devices:
-
-\begin{lstlisting}[language=C,numbers=left]
-  if (dev != rtl_ec_net_dev) {
-          if (tp->phys[0] >= 0) {
-                  mii_check_media(&tp->mii, netif_msg_link(tp),
-                                  init_media);
-          }
-  } else {
-          void __iomem *ioaddr = tp->mmio_addr;
-          uint16_t link = RTL_R16(BasicModeStatus)
-                          & BMSR_LSTATUS;
-          ecdev_link_state(rtl_ec_dev, link ? 1 : 0);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] The ``media check'' is done
-  via the media independent interface (MII\nomenclature{MII}{Media
-    Independent Interface}), a standard interface for Fast Ethernet
-  devices.
-\item[\normalfont\textcircled{\tiny 7} -- \textcircled{\tiny 10}] For
-  EtherCAT devices, the link state is fetched manually from the
-  appropriate device register, and passed to the EtherCAT master by
-  calling \textit{ecdev\_\-link\_\-state()}.
-\end{description}
-
-\paragraph{Module Cleanup}
-
-Below is the module's cleanup function:
-
-\begin{lstlisting}[language=C,numbers=left]
-  static void __exit rtl8139_cleanup_module (void)
-  {
-          printk(KERN_INFO "Cleaning up RTL8139-EtherCAT"
-                 " module...\n");
-
-          if (rtl_ec_net_dev) {
-                  printk(KERN_INFO "Stopping device...\n");
-                  ecdev_stop(ec_device_master_index);
-                  printk(KERN_INFO "Unregistering device...\n");
-                  ecdev_unregister(ec_device_master_index,
-                                   rtl_ec_dev);
-                  rtl_ec_dev = NULL;
-          }
-
-          pci_unregister_driver(&rtl8139_pci_driver);
-
-          printk(KERN_INFO "RTL8139-EtherCAT module"
-                 " cleaned up.\n");
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 6}] Stopping and unregistration is
-  only done, if a device was registered before.
-\item[\normalfont\textcircled{\tiny 8}] The master is first stopped,
-  so it does not access the device any more.
-\item[\normalfont\textcircled{\tiny 10}] After this, the device is
-  unregistered. The master is now ``ophaned''.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{The Master Module}
-\label{sec:mastermod}
-\index{Master module}
-
-The EtherCAT master is designed to run as a kernel module. Moreover
-the master kernel module \textit{ec\_master} can handle multiple
-masters at the same time: The number of masters has to be passed to
-the module with the parameter \textit{ec\_master\_count}, that
-defaults to $1$. A certain master can later be addressed by its index.
-For example, if the master module has been loaded with the command
-
-\begin{lstlisting}
-  host# `\textbf{modprobe ec\_master ec\_master\_count=2}`
-\end{lstlisting}
-
-the two masters can be addressed by their indices 0 and 1 respectively
-(see figure~\ref{fig:masters}). This master index mandatory for
-certain functions of the master interfaces.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.5\textwidth]{images/masters}
-  \caption{Multiple masters in one module}
-  \label{fig:masters}
-\end{figure}
-
-\paragraph{Master Log Messages}
-
-The master module gives information about it's state and events via
-the syslog interface. The module loading command above should result
-in the following syslog messages:
-
-\begin{lstlisting}
-  EtherCAT: Master driver, 1.1 (stable) - rev. 513,
-            compiled by fp at Aug  09 2006 09:43:50
-  EtherCAT: Initializing 2 EtherCAT master(s)...
-  EtherCAT: Initializing master 0.
-  EtherCAT: Initializing master 1.
-  EtherCAT: Master driver initialized.
-\end{lstlisting}
-
-The master provides information about it's version number, subversion
-revision number and compile information, like the date of compilation
-and the user, who compiled. All messages are prefixed either with
-\texttt{EtherCAT:}, \texttt{EtherCAT WARNING:} or \texttt{EtherCAT
-  ERROR:}, which makes searching the logs easier.
-
-%------------------------------------------------------------------------------
-
-\subsection{Class Reference}
-\label{sec:classes}
-
-This section is not intended to be a complete reference of master
-classes and functions\footnote{The comprehensive master reference can
-  be obtained at http://etherlab.org/download/download-en.html}, but
-will give a general survey of the master's classes, and how they
-interact.
-
-Figure~\ref{fig:uml-all} shows an UML class diagram of the master
-classes.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=\textwidth]{images/uml-all}
-  \caption{UML class diagram with associations}
-  \label{fig:uml-all}
-\end{figure}
-
-The following subsections introduce serveral classes with their
-attributes and methods.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Master Class}
-\label{sec:class-master}
-\index{Master!Class}
-
-Figure~\ref{fig:uml-master} shows an UML class diagram of the master
-class. There is a short explanation of the attributes and methods
-below.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.8\textwidth]{images/uml-master}
-  \caption{Master UML class diagram}
-  \label{fig:uml-master}
-\end{figure}
-
-\paragraph{Master Attributes}
-
-\begin{description}
-\item[list] is a listhead structure that is needed to manage the list
-  of masters in the master module (see section~\ref{sec:mastermod}).
-\item[reserved] is a flag, that marks the master as reserved for a
-  realtime module, so that a call to \textit{ecrt\_request\_master()}
-  fails, if another module is already using the master.
-\item[index] contains the number of the master. The first master will
-  get index 0, the second index 1, and so on.
-\item[kobj] In order to make the master object available via Sysfs
-  (see section~\ref{sec:sysfs}), this structure is needed inside the
-  master object (see section~\ref{sec:sysfs}).
-\item[slaves] is the list of slaves. It consists of objects of the
-  \textit{ec\_slave\_t} class (see section~\ref{sec:class-slave}).
-\item[slave\_count] is the number of slaves in the list.
-\item[device] points to the network device that is used by the master
-  to send and receive frames (see section~\ref{sec:class-device}). It
-  is \textit{NULL}, if no device is connected.
-\item[datagram\_queue] is a list of datagrams (see
-  section~\ref{sec:class-datagram}) that have to be sent by the
-  master, or have already been sent and wait to be received again.
-  Upon reception or error, the datagrams are dequeued.
-\item[datagram\_index] contains the index value for the next datagram.
-  The master stores this incrementing index into every datagram, to
-  make it easier to assign a received datagram to the one sent before.
-\item[domains] contains the list of domains created by the realtime
-  module (section~\ref{sec:class-domain}).
-\item[debug\_level] controls, how much debugging output is printed by
-  the master: 0 means no debugging output, 1 means to output certain
-  executing marks and actions, and 2 means to output frame contents in
-  addition. This value can be changed at runtime via the Sysfs
-  interface (see section~\ref{sec:sysfs}).
-\item[stats] is a statistics object that contains certain counters
-  (like the number of missed frames).  These statistics are output on
-  demand, but at most once a second.
-\item[workqueue] is the kernel workqueue used for idle mode.
-\item[idle\_work] is the work object, that is queued.
-\item[fsm] The attribute \textit{fsm} represents the master's finite
-  state machine, that does all the slave processing. See
-  sections~\ref{sec:class-fsm} and~\ref{sec:fsm} for further details.
-\item[mode] contains the current master mode, if it is orphaned, idle,
-  or in operation mode.
-\item[eoe\_timer] is the kernel timer used for EoE\index{EoE}
-  processing.
-\item[eoe\_running] marks the state of EoE processing.
-\item[eoe\_handlers] is the list of EoE handlers (see
-  section~\ref{sec:class-eoe}).
-\item[internal\_lock] is a spinlock used in idle mode, that controls
-  the concurrency of the idle and EoE processes.
-\item[request\_cb] The ``request lock'' callback function, the master
-  has to provide for foreign instances, which want to access the
-  master (see section~\ref{sec:concurr}).
-\item[release\_cb] The callback function that will release the master
-  lock.
-\item[cb\_data] This value will be passed as an argument to each
-  callback.
-\item[eeprom\_write\_enable] flag can be written via Sysfs to enable
-  the general writing of E$^2$PROM contents.
-\end{description}
-
-\paragraph{Public Master Methods}
-
-\begin{description}
-\item[ec\_master\_init()] is the master's constructor. It initializes
-  all attributes, creates the workqueue, creates EoE handlers and the
-  state machine object, and adds the kernel object to the Sysfs
-  hierarchy.
-\item[ec\_master\_clear()] is the destructor and undoes all these
-  actions.
-\item[ec\_master\_reset()] clears the master, but initializes it
-  again. This is needed, when a realtime module disconnects: Slaves
-  and other attributes are cleared and are later rebuilt by the idle
-  process.
-\item[ec\_master\_idle\_start/stop()] These methods enable or disable
-  the idle process.
-\item[ec\_master\_eoe\_start/stop()] These methods do the same for the
-  EoE timer.
-\item[ec\_master\_receive\_datagrams()] This method is called by the
-  device, which uses it to pass received frames to the master.  The
-  frame is dissected and the contained datagrams are assigned to the
-  datagram objects in the datagram queue, which are dequeued on
-  reception or error.
-\item[ec\_master\_queue\_datagram()] This method is used to queue a
-  new datagram for sending and receiving.
-\item[ec\_master\_output\_stats()] This method is cyclically called to
-  output a summary of the \textit{stats} attribute at most once a
-  second.
-\item[ec\_master\_clear\_slaves()] clears the list of slaves. This is
-  needed on connection/disconnection of a realtime module or at a
-  topology change in idle mode, when all slaves objects are rebuilt.
-\end{description}
-
-\paragraph{Private Master Methods}
-
-A few of a master's methods are private, meaning, that they can only
-be called from other master methods:
-
-\begin{description}
-\item[ec\_master\_send\_datagrams()] searches the datagram queue for
-  unsent datagrams, allocates frames to send them, does the actual
-  sending and marks the datagrams as sent.
-\item[ec\_master\_idle\_run()] is the work function for the idle mode.
-  It executes the idle state machine, described in
-  section~\ref{sec:fsm-idle}.
-\item[ec\_master\_eoe\_run()] is called by the EoE timer and is
-  responsible for communicating with EoE-capable slaves. See
-  section~\ref{sec:eoeimp} for more information.
-\end{description}
-
-\paragraph{Master Methods (Realtime Interface)}
-
-The master methods belonging to the Eth\-er\-CAT realtime
-interface\index{ecrt@\textit{ecrt}}\nomenclature{ecrt}{EtherCAT
-  Realtime Interface} begin with the prefix \textit{ecrt} instead of
-\textit{ec}. The functions of the realtime interface are explained in
-section~\ref{sec:ecrt-master}.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Slave Class}
-\label{sec:class-slave}
-\index{Slave!Class}
-
-Figure~\ref{fig:uml-slave} shows an UML class diagram of the slave
-class. There is a short explanation of the attributes and methods
-below.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.8\textwidth]{images/uml-slave}
-  \caption{Slave UML class diagram}
-  \label{fig:uml-slave}
-\end{figure}
-
-\paragraph{Slave Attributes}
-
-\begin{description}
-\item[list] The master holds a slave list, therefore the slave class
-  must contain this structure used as an anchor for the linked
-  list.
-\item[kobj] This pointer serves as base object for the slave's Sysfs
-  representation.
-\item[master] is the pointer to the master owning this slave object.
-\item[ring\_position] is the logical position in the logical ring
-  topology.
-\item[station\_address] is the configured station address. This is
-  always the ring position~+~$1$).
-\item[coupler\_index] is the index of the last bus coupler.
-\item[coupler\_subindex] is the slave's position, counted from the
-  last bus coupler. See section~\ref{sec:addr} for more information.
-\item[base\_*] These attributes contain base information about the
-  slave, that are read from the ``DL Information'' attribute.
-\item[dl\_*] These fields store information of the ``DL Status''
-  attribute, for example states of the the communication ports.
-\item[sii\_*] These attributes contain values from the ``Slave
-  Information Interface'' \cite[section~6.4]{dlspec}, mostly identity
-  and mailbox information, but also the list of sync manager
-  configurations and PDOs.
-\item[registered] This flag is set, if one or more PDOs of the slave
-  have been registered for process data exchange. Otherwise a warning
-  is output, because the slave is unused.
-\item[fmmus] Is an array of FMMU configurations, that have to be
-  applied to the slave.
-\item[fmmu\_count] contains number of FMMUs used.
-\item[eeprom\_*] These fields contain E$^2$PROM contents and the
-  extracted category information \cite[section~5.4]{alspec}.
-\item[new\_eeprom\_data] If this pointer is not \textit{NULL}, it
-  points to new E$^2$PROM contents, that have to be written to the
-  slave.
-\item[new\_eeprom\_size] This field represents the size of the new
-  E$^2$PROM data.
-\item[requested\_state] is the requested slave state.
-\item[current\_state] is the current slave state.
-\item[error\_flag] is used by the operation and idle state machines
-  to indicate, that a state transisition has failed and should not be
-  tried again until an external event happens.
-\item[online] This flag contains the online state of the slave (i.~e.
-  if it currently responds to the masters commands). Changes of the
-  online state are always reported.
-\item[varsize\_fields] is only suitable for slaves that provide PDOs
-  of variable size (like slaves that manage a sub-fieldbus) and
-  contains information about what size this fields actually should
-  have.
-\end{description}
-
-\paragraph{Public Slave Methods}
-
-\begin{description}
-\item[ec\_slave\_init()] The slave's constructor.
-\item[ec\_slave\_clear()] The slave's destructor.
-\item[ec\_prepare\_fmmu()] prepares an FMMU configuration. The FMMU is
-  configured for a certain sync manager and domain.
-\item[ec\_fetch\_*()] Serveral methods to extract information of the
-  E$^2$PROM category contents.
-\item[ec\_slave\_locate\_string()] extracts a string out of a STRING
-  category and allocates string memory.
-\item[ec\_slave\_calc\_sync\_size()] calculates the size of sync
-  manager contents, because they can be variable due to variable-sized
-  PDOs.
-\item[ec\_slave\_info()] This method prints all slave information into
-  a buffer for Sysfs reading.
-\item[ec\_slave\_mbox\_*()] These functions prepare datagrams for
-  mailbox communication, or process mailbox responses, respectively.
-\end{description}
-
-\paragraph{Private Slave Methods}
-
-\begin{description}
-\item[ec\_slave\_write\_eeprom()] This function accepts E$^2$PROM data
-  from user space, does a quick validation of the contents and
-  schedules them for writing through the idle state machine.
-\end{description}
-
-\paragraph{Slave Methods (Realtime Interface)}
-
-\begin{description}
-\item[ecrt\_slave\_conf\_sdo*()] These methods accept SDO
-  configurations, that are applied on slave activation (i.~e.
-  everytime the slave is configured). The methods differ only in the
-  data size of the SDO (8, 16 or 32 bit).
-\item[ecrt\_slave\_pdo\_size()] This method specifies the size of a
-  variable-sized PDO.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Device Class}
-\label{sec:class-device}
-\index{Device!Class}
-
-The device class is responsible for communicating with the connected
-EtherCAT-enabled network driver. Figure~\ref{fig:uml-device} shows its
-UML class diagram.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.3\textwidth]{images/uml-device}
-  \caption{Device UML class diagram}
-  \label{fig:uml-device}
-\end{figure}
-
-\paragraph{Device Attributes}
-
-\begin{description}
-\item[master] A pointer to the master, which owns the device object.
-\item[dev] This is the pointer to the \textit{net\_device} structure
-  of the connected network device driver.
-\item[open] This flag stores, if the network device is ``opened'' and
-  ready for transmitting and receiving frames.
-\item[tx\_skb] The transmittion socket buffer. Instead of allocating a
-  new socket buffer for each frame, the same socket buffer is recycled
-  and used for every frame.
-\item[isr] The pointer to the network device's interrupt service
-  routine. \textit{ec\_isr\_t} is a type definition in the device
-  interface, which looks like below:
-  \begin{lstlisting}[gobble=4,language=C]
-    typedef irqreturn_t (*ec_isr_t)(int, void *,
-                                    struct pt_regs *);
-  \end{lstlisting}
-\item[module] A pointer to the network driver module, to increase and
-  decrease the use counter (see paragraph ``Implicit Dependencies'' in
-  section~\ref{sec:ecdev}).
-\item[link\_state] The current link state. It can be 0 ``down'' or 1
-  ``up''.
-\item[dbg] Every device objects contains a debugging interface (see
-  sectios~\ref{sec:class-debug} and~\ref{sec:debug}).
-\end{description}
-
-\paragraph{Public Device Methods}
-
-\begin{description}
-\item[ec\_device\_init()] The device constructor.
-\item[ec\_device\_clear()] The device destructor.
-\item[ec\_device\_open()] ``Opens'' the device for transmittion and
-  reception of frames. This is equivalent to the \textit{ifconfig up}
-  command for ordinary Ethernet devices.
-\item[ec\_device\_close()] Stops frame transmittion and reception.
-  This is equivalent to the \textit{ifconfig down} command for
-  ordinary Ethernet devices.
-\item[ec\_device\_call\_isr()] Calls the interrupt service routine of
-  the device.
-\item[ec\_device\_tx\_data()] Returns a pointer into the memory of the
-  transmittion socket buffer \textit{tx\_skb}. This is used by the
-  master to assemble a new EtherCAT frame.
-\item[ec\_device\_send()] Sends an assembled frame by passing it to
-  the device's \textit{hard\_\-start\_\-xmit()} callback.
-\end{description}
-
-\paragraph{Device Methods (Device Interface)}
-
-The device methods belonging to the device interface are explained in
-section~\ref{sec:ecdev}.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Datagram Class}
-\label{sec:class-datagram}
-\index{Datagram!Class}
-
-So send and receive a datagram, an object of the
-\textit{ec\_datagram\_t} class is needed. It can be initialized with a
-datagram type \cite[section~5.4]{dlspec} and length (optionally filled
-with data) and appended to the master's datagram queue.
-Figure~\ref{fig:uml-datagram} shows its UML class diagram.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.3\textwidth]{images/uml-datagram}
-  \caption{Datagram UML class diagram}
-  \label{fig:uml-datagram}
-\end{figure}
-
-\paragraph{Datagram Attributes}
-
-\begin{description}
-\item[list] This attribute is needed to make a list of datagrams, as
-  used in the domain class (see section~\ref{sec:class-domain}).
-\item[queue] This attribute is the anchor to the master's datagram
-  queue, which is implemented as a linked list.
-\item[type] The datagram type. \textit{ec\_\-datagram\_\-type\_\-t} is
-  an enumeration, which can have the values
-  \textit{EC\_\-DATAGRAM\_\-APRD}, \textit{EC\_\-DATAGRAM\_\-APWR},
-  \textit{EC\_\-DATAGRAM\_\-NPRD}, \textit{EC\_\-DATAGRAM\_\-NPWR},
-  \textit{EC\_\-DATAGRAM\_\-BRD}, \textit{EC\_\-DATAGRAM\_\-BWR} or
-  \textit{EC\_\-DATAGRAM\_\-LRW}.
-\item[address] The slave address. For all addressing schemes take 4
-  bytes, \textit{ec\_address\_t} is a union type:
-  \begin{lstlisting}[gobble=4,language=C]
-    typedef union {
-            struct {
-                    uint16_t slave; /**< configured or
-                                         autoincrement
-                                         address */
-                    uint16_t mem; /**< physical memory
-                                       address */
-            } physical; /**< physical address */
-            uint32_t logical; /**< logical address */
-    } ec_address_t;
-  \end{lstlisting}
-\item[data] The actual data of the datagram. These are either filled
-  in before sending (at writing access) or are inserted by the
-  adressed slave(s) (at reading access). In any case, the data memory
-  must be dynamically allocated. Besides, this can be done before
-  cyclic processing with the \textit{ec\_datagram\_prealloc()} method
-  (see below).
-\item[mem\_size] The size of the allocated memory, \textit{data}
-  points to.
-\item[data\_size] The size of the actual data in the \textit{data}
-  memory.
-\item[index] The sequential EtherCAT datagram index. This value is set
-  by the master on sending, to easier assign a received datagram to a
-  queued datagram object.
-\item[working\_counter] The working counter of the datagram. This is
-  set to zero on sending and filled with the real value of the working
-  counter on datagram reception.
-\item[state] The state of the datagram.
-  \textit{ec\_\-datagram\_\-state\_\-t} is an enumeration and can be
-  \textit{EC\_\-DATA\-GRAM\_\-INIT},
-  \textit{EC\_\-DATA\-GRAM\_\-QUEU\-ED},
-  \textit{EC\_\-DATA\-GR\-AM\_\-SEN\-T},
-  \textit{EC\_\-DATA\-GRAM\_\-REC\-EIVED},
-  \textit{EC\_\-DATA\-GRAM\_\-TIMED\_\-OUT} or
-  \textit{EC\_\-DA\-TA\-GRAM\_\-ERR\-OR}.
-\item[t\_sent] This attribute is set to the timestamp, when the
-  datagram was sent, to later detect a timeout.
-\end{description}
-
-\paragraph{Public Datagram Methods}
-
-\begin{description}
-\item[ec\_datagram\_init()] The datagram's constructor.
-\item[ec\_datagram\_clear()] The datagram's destructor.
-\item[ec\_datagram\_prealloc()] Allocates memory for the datagram
-  data. This is especially needed, if the datagram structure will
-  later be used in a context, where no dynamic memory allocation is
-  allowed.
-\item[ec\_datagram\_nprd()] Initializes a ``Node-Addressed Physical
-  Read'' datagram \cite[section~5.4.1.2]{dlspec}.
-\item[ec\_datagram\_npwr()] Initializes a ``Node-Addressed Physical
-  Write'' datagram \cite[section~5.4.2.2]{dlspec}.
-\item[ec\_datagram\_aprd()] Initializes a ``Auto-Increment Physical
-  Read'' datagram \cite[section~5.4.1.1]{dlspec}.
-\item[ec\_datagram\_apwr()] Initializes a ``Auto-Increment Physical
-  Write'' datagram \cite[section~5.4.2.1]{dlspec}.
-\item[ec\_datagram\_brd()] Initializes a ``Broadcast Read'' datagram
-  \cite[section~5.4.1.3]{dlspec}.
-\item[ec\_datagram\_bwr()] Initializes a ``Broadcast Write'' datagram
-  \cite[section~5.4.2.3]{dlspec}.
-\item[ec\_datagram\_lrw()] Initializes a ``Logical ReadWrite''
-  datagram \cite[section~5.4.3.4]{dlspec}.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Domain Class}
-\label{sec:class-domain}
-\index{Domain!Class}
-
-The domain class encapsules PDO registration and management of the
-process data image and its exchange. The UML class diagram can be seen
-in figure~\ref{fig:uml-domain}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.4\textwidth]{images/uml-domain}
-  \caption{Domain UML class diagram}
-  \label{fig:uml-domain}
-\end{figure}
-
-\paragraph{Domain Attributes}
-
-\begin{description}
-\item[kobj] This \textit{kobject} structure is needed for the Sysfs
-  representation of the domain.
-\item[list] The master manages a list of domains, so this list anchor
-  is needed.
-\item[index] The domain's index. The first domain will get index 0,
-  the second index 1, and so on.
-\item[master] A pointer to the master owning the domain.
-\item[data\_size] The size of the domain's process data image.
-\item[datagram] A linked list with the datagram objects, the domain
-  needs for process data exchange (see
-  section~\ref{sec:class-datagram}).
-\item[base\_address] This attribute stores the logical offset, to
-  which the domain's process data are mapped.
-\item[response\_count] The sum of the datagrams' working counters at
-  the last process data exchange. Changes are always reported.
-\item[data\_regs] The (linked) list of PDO registrations. The realtime
-  module requests the exchange of certain PDOs and supplies the
-  address of process data pointers, that will later point to the
-  respective locations in the process data image. These ``data
-  registrations'' are saved in the \textit{data\_regs} list.
-\item[working\_counter\_changes] This field stores the number of
-  working counter changes since the last notification. This helps to
-  reduce syslog output in case of frequent changes.
-\item[t\_last] The timestamp of the last working counter change
-  notification.
-\end{description}
-
-\paragraph{Public Domain Methods}
-
-\begin{description}
-\item[ec\_domain\_init()] The domain's constructor.
-\item[ec\_domain\_clear()] The domain's destructor.
-\item[ec\_domain\_alloc()] Allocates the process data image and the
-  respective datagrams based on the process data registrations.
-\item[ec\_domain\_queue()] Queues the domain's datagrams for exchange
-  via the master.
-\end{description}
-
-\paragraph{Private Domain Methods}
-
-\begin{description}
-\item[ec\_domain\_reg\_pdo\_entry()] This method is used to do a PDO
-  registration. It finds the appropriate sync manager covering the PDO
-  data, calculates its offset in the sync-manager-protected memory and
-  prepares the FMMU configurations for the related slave. Then the PDO
-  registration is appended to the list.
-\item[ec\_domain\_clear\_data\_regs()] Clearing all process data
-  registrations is needed in serveral places and therefore has been
-  sourced out to an own method.
-\item[ec\_domain\_add\_datagram()] This methods allocates a datagram
-  and appends it to the list. This is done during domain allocation.
-\end{description}
-
-\paragraph{Domain Methods (Realtime Interface)}
-
-The domain methods belonging to the realtime interface are introduced
-in section~\ref{sec:ecrt-domain}.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Finite State Machine Class}
-\label{sec:class-fsm}
-\index{FSM!Class}
-
-This class encapsules all state machines, except the EoE state
-machine. Its UML class diagram can be seen in
-figure~\ref{fig:uml-fsm}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/uml-fsm}
-  \caption{Finite State Machine UML class diagram}
-  \label{fig:uml-fsm}
-\end{figure}
-
-\paragraph{FSM Attributes}
-
-\begin{description}
-\item[master] A pointer to the master owning the FSM object.
-\item[slave] Serveral sub state machines are executed for single
-  slaves. This pointer stores the current slave for these FSMs.
-\item[datagram] The FSM class has its own datagram, which is used in
-  every state and sub-state.
-\item[master\_state] This function pointer stores the current state
-  function for one of the master's state machines.
-\item[master\_slaves\_responding] This attribute is used in the
-  operation state machine (see section~\ref{sec:fsm-op}) to store the
-  number of slaves, that responded to the last broadcast command.
-\item[master\_slave\_states] This attribute stores the slave states,
-  that were determined by the last broadcast command.
-\item[master\_validation] This flag is used by the operation state
-  machine and is non-zero, if a bus validation has to be done.
-\item[slave\_state] This function pointer stores the current state of
-  the slave scan state machine (see section~\ref{sec:fsm-scan}) or the
-  slave configuration state machine (see section~\ref{sec:fsm-conf}).
-\item[sii\_state] This function pointer stores the current state of
-  the SII state machine (see section~\ref{sec:fsm-sii}).
-\item[sii\_offset] This attribute is used by the SII state machine to
-  store the word address for the current read or write cycle.
-\item[sii\_mode] If this attribute is zero, the SII access is done
-  with ``auto-increment'' datagrams \cite[section~5.4]{dlspec}.
-  If it is non-zero, ``station-address'' datagrams are used.
-\item[sii\_value] This attribute stores the value to write, or the
-  read value, respectively.
-\item[sii\_start] A timestamp attribute, that stores the beginning
-  time of an SII operation to detect a timeout.
-\item[change\_state] This function pointer stores the current state of
-  the state change state machine.
-\item[change\_new] This attribute stores the requested state for the
-  state change state machine.
-\item[change\_start] A timestamp attribute to detect a timeout while
-  changing slave states.
-\item[coe\_state] This function pointer stores the current state of
-  the CoE state machines.
-\item[sdodata] This is an SDO data object that stores information
-  about the current SDO to write.
-\item[coe\_start] A timestamp attribute to detect timeouts during CoE
-  configuration.
-\end{description}
-
-\paragraph{Public FSM Methods}
-
-\begin{description}
-\item[ec\_fsm\_init()] Constructor of the FSM class.
-\item[ec\_fsm\_clear()] Destructor of the FSM class.
-\item[ec\_fsm\_reset()] Resets the whole FSM object. This is needed to
-  restart the master state machines.
-\item[ec\_fsm\_execute()] Executes one state of the current state
-  machine and then returns.
-\item[ec\_fsm\_startup()] Initializes the master startup state
-  machine, which determines the number of slaves and executes the
-  slave scan state machine for each slave.
-\item[ec\_fsm\_startup\_running()] Returns non-zero, if the startup
-  state machine did not terminate yet.
-\item[ec\_fsm\_startup\_success()] Returns non-zero, if the startup
-  state machine terminated with success.
-\item[ec\_fsm\_configuration()] Initializes the master configuration
-  state machine, which executes the slave configuration state machine
-  for each slave.
-\item[ec\_fsm\_configuration\_running()] Returns non-zero, if the
-  configuration state machine did not terminate yet.
-\item[ec\_fsm\_configuration\_success()] Returns non-zero, if the
-  configuration state machine terminated with success.
-\end{description}
-
-\paragraph{FSM State Methods}
-
-The rest of the methods showed in the UML class diagram are state
-methods of the state machines. These states are described in
-section~\ref{sec:fsm}.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The EoE Class}
-\label{sec:class-eoe}
-\index{EoE!Class}
-
-Objects of the \textit{ec\_eoe\_t} class are called EoE handlers. Each
-EoE handler represents a virtual network interface and can be coupled
-to a EoE-capable slave on demand. The UML class diagram can be seen in
-figure~\ref{fig:uml-eoe}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.4\textwidth]{images/uml-eoe}
-  \caption{EoE UML class diagram}
-  \label{fig:uml-eoe}
-\end{figure}
-
-\paragraph{EoE Attributes}
-
-\begin{description}
-\item[list] The master class maintains a list of EoE handlers.
-  Therefore this list anchor is needed.
-\item[slave] If an EoE handler is coupled to a slave, this pointer
-  points to the related slave object. Otherwise it is \textit{NULL}.
-\item[datagram] Every EoE handler owns a datagram object to exchange
-  data with the coupled slave via its state machine.
-\item[state] This function pointer points to the current state of the
-  EoE state machine (see section~\ref{sec:eoeimp}).
-\item[dev] A pointer to the \textit{net\_device} structure that
-  represents the network interface to the kernel.
-\item[stats] The statistics object for the network interface.
-\item[opened] This flag stores, if the network interface was opened.
-  No EoE processing will be done, if the device is not opened.
-\item[t\_last] This timestamp attribute stores the time of the last
-  bit rate measurement.
-\item[rx\_skb] A pointer to the current receive socket buffer. On
-  every first fragment of a received frame, a new receive socket
-  buffer is allocated. On every last fragment, this buffer will be
-  passed to the network stack.
-\item[rx\_skb\_offset] This attribute stores the offset for the next
-  fragment data in the receive socket buffer.
-\item[rx\_skb\_size] This attribute stores the current data size of
-  the receive socket buffer.
-\item[rx\_expected\_fragment] The expected number of the next
-  fragment. If a fragment with an invalid number is received, the
-  whole frame will be dropped.
-\item[rx\_counter] This is the sum of the octets received since the
-  last bit rate measurement.
-\item[rx\_rate] This attribute stores the receive bit rate in bps.
-\item[tx\_queue] Each EoE handler maintains a transmittion queue for
-  frames, that come in via the network interface. This queue is
-  implemented with a linked list and protected by a spinlock.
-\item[tx\_queue\_active] This flag stores, if the transmittion queue
-  is currently accepting frames from the network stack. If the queue
-  gets filled up, frame transmittion is suspended with a call to
-  \textit{netif\_stop\_queue()}. If the fill state decreases below the
-  half capacity, frame transmittion is restarted with
-  \textit{netif\_wake\_queue()}.
-\item[tx\_queued\_frames] The number of frames in the transmittion
-  queue.
-\item[tx\_queue\_lock] The spinlock used to protect the transmittion
-  queue. This is needed, because the queue is accessed both from
-  network stack context and from the master's EoE timer.
-\item[tx\_frame] The frame that is currently sent. The
-  \textit{ec\_eoe\_frame\_t} structure combines the socket buffer
-  structure with a list head to append it to the transmittion queue.
-\item[tx\_frame\_number] The EoE protocol demands to maintain a
-  sequencial frame number, that must be increased with every frame
-  sent.
-\item[tx\_fragment\_number] The sequencial number of the next fragment
-  to transmit.
-\item[tx\_offset] Current frame data offset for the next fragment to
-  transmit.
-\item[tx\_counter] The number of octets transferred since the last bit
-  rate measurement.
-\item[tx\_rate] The recent transmittion bit rate in bps.
-\end{description}
-
-\paragraph{Public EoE Methods}
-
-\begin{description}
-\item[ec\_eoe\_init()] The EoE handler's constructor. The network
-  interface is allocated and registered.
-\item[ec\_eoe\_clear()] The EoE handler's destructor. The network
-  interface is unregistered and all allocated memory is freed.
-\item[ec\_eoe\_run()] Executes the EoE state machine (see
-  section~\ref{sec:eoeimp}) for this handler.
-\item[ec\_eoe\_active()] Returns true, if the handler has a slave
-  coupled and the network interface is opened.
-\end{description}
-
-\paragraph{Private EoE Methods}
-
-\begin{description}
-\item[ec\_eoe\_flush()] Clears the transmittion queue and drops all
-  frames queued for sending.
-\item[ec\_eoe\_send()] Sends one fragment of the current frame.
-\end{description}
-
-
-\paragraph{EoE State Methods}
-
-The rest of the private methods are state functions for the EoE state
-machine, which is discussed in section~\ref{sec:eoeimp}.
-
-%------------------------------------------------------------------------------
-
-\subsubsection{The Debug Class}
-\label{sec:class-debug}
-
-The debug class maintains a virtual network interface. All frames that
-are sent and received by the master will be forwarded to this network
-interface, so that bus monitoring can be done with third party tools
-(see section~\ref{sec:debug}). Figure~\ref{fig:uml-debug} shows the
-UML class diagram.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.3\textwidth]{images/uml-debug}
-  \caption{Debug UML class diagram}
-  \label{fig:uml-debug}
-\end{figure}
-
-\paragraph{Debug Attributes}
-
-\begin{description}
-\item[dev] A pointer to the allocated \textit{net\_device} structure
-  that represents the network interface in the kernel.
-\item[stats] An object for interface statistics.
-\item[opened] Stores the state of the device. Frames will only be
-  forwarded, if the device was opened with the \textit{ifconfig up}
-  command (or something similar).
-\end{description}
-
-\paragraph{Public Debug Methods}
-
-\begin{description}
-\item[ec\_debug\_init()] The constructor.
-\item[ec\_debug\_clear()] The destructor.
-\item[ec\_debug\_send()] This method forwards a frame to the virtual
-  network interface. It dynamically allocates a new socket buffer and
-  passes it to the network stack.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The Realtime Interface}
-\label{sec:ecrt}
-\index{Realtime interface}
-
-The realtime interface provides functions and data structures for
-realtime modules to access and use an EtherCAT master.
-
-\subsubsection{Master Requesting and Releasing}
-
-Before a realtime module can access am EtherCAT master provided by the
-master module, it has to reserve one for exclusive use. After use, it
-has to release the requested master and make it available for other
-modules. This is done with the following functions:
-
-\begin{lstlisting}[language=C]
-  ec_master_t *ecrt_request_master(unsigned int master_index);
-  void ecrt_release_master(ec_master_t *master);
-\end{lstlisting}
-
-The \textit{ecrt\_request\_master()} function has to be the first
-function a module has to call, when using EtherCAT. The function takes
-the index of the master as its argument. The first master has index 0,
-the $n$th master has index $n - 1$. The number of existent masters has
-to be specified when loading the master module (see
-section~\ref{sec:mastermod}). The function tries to reserve the
-specified master and scans for slaves. It returns a pointer to the
-reserved master object upon success, or \textit{NULL} if an error
-occured.
-
-The \textit{ecrt\_release\_master()} function releases a reserved
-master after use. It takes the pointer to the master object returned
-by \textit{ecrt\_request\_master()} as its argument and can never
-fail.
-
-\subsubsection{Master Methods}
-\label{sec:ecrt-master}
-
-\paragraph{Domain Creation}
-
-For process data exchange, at least one process data domain is needed
-(see section~\ref{sec:processdata}).
-
-\begin{lstlisting}[language=C]
-  ec_domain_t *ecrt_master_create_domain(ec_master_t *master);
-\end{lstlisting}
-
-The \textit{ecrt\_master\_create\_domain()} method creates a new
-process data domain and returns a pointer to the new domain object.
-This object can be used for registering process data objects and
-exchange process data in cyclic operation. On failure, the function
-returns \textit{NULL}.
-
-\paragraph{Slave Handlers}
-
-To access a certain slave, there is a method to get a slave handler:
-
-\begin{lstlisting}[language=C]
-  ec_slave_t *ecrt_master_get_slave(const ec_master_t *,
-                                    const char *);
-\end{lstlisting}
-
-The \textit{ecrt\_master\_get\_slave()} method returns a pointer to a
-certain slave object, specified by its ASCII address (see
-section~\ref{sec:addr}). If the address is invalid, \textit{NULL} is
-returned.
-
-\paragraph{Master Activation}
-
-When all domains are created, and all process data objects are
-registered, the master can be activated:
-
-\begin{lstlisting}[language=C]
-  int ecrt_master_activate(ec_master_t *master);
-  void ecrt_master_deactivate(ec_master_t *master);
-\end{lstlisting}
-
-By calling the \textit{ecrt\_master\_activate()} method, all slaves
-are configured according to the prior method calls and are brought
-into \textit{OP} state. In this case, the method has a return value of
-0. Otherwise (wrong configuration or bus failure) the method returns
-non-zero.
-
-The \textit{ecrt\_master\_deactivate()} method is the counterpart to
-the activate call: It brings all slaves back into \textit{INIT} state
-again. This method should be called prior to
-\textit{ecrt\_\-master\_\-release()}.
-
-\paragraph{Locking Callbacks}
-
-For concurrent master access, the realtime module has to provide a
-locking mechanism (see section~\ref{sec:concurr}):
-
-\begin{lstlisting}[language=C]
-  void ecrt_master_callbacks(ec_master_t *master,
-                             int (*request_cb)(void *),
-                             void (*release_cb)(void *),
-                             void *cb_data);
-\end{lstlisting}
-
-The ``request lock'' and ``release lock'' callbacks can be set with
-the \textit{ecrt\_master\_call\-backs()} method. It takes two function
-pointers and a data value as additional arguments. The arbitrary data
-value will be passed as argument on every callback. Asynchronous
-master access (like EoE processing) is only possible if these
-callbacks have been set.
-
-\paragraph{Preparation of Cyclic Data Exchange}
-
-Cyclic operation mostly consists of the three steps input, processing
-and output. In EtherCAT terms this would mean: Receive datagrams,
-evaluate process data and send datagrams. The first cycle differs from
-this principle, because no datagrams have been sent yet, so there is
-nothing to receive. To avoid having a case differantiation (in terms
-of an \textit{if} clause), the following method exists:
-
-\begin{lstlisting}[language=C]
-  void ecrt_master_prepare(ec_master_t *master);
-\end{lstlisting}
-
-As a last thing before cyclic operation, a call to the
-\textit{ecrt\_master\_prepare()} method should be issued. It makes all
-process data domains queue their datagrams and issues a send command,
-so that the first receive call in cyclic operation will not fail.
-
-\paragraph{Frame Sending and Receiving}
-
-To send all queued datagrams and to later receive the sent datagrams
-there are two methods:
-
-\begin{lstlisting}[language=C]
-  void ecrt_master_send(ec_master_t *master);
-  void ecrt_master_receive(ec_master_t *master);
-\end{lstlisting}
-
-The \textit{ecrt\_master\_send()} method takes all datagrams, that
-have been queued for transmission, packs them into frames, and passes
-them to the network device for sending.
-
-The \textit{ecrt\_master\_receive()} queries the network device for
-received frames (by calling the ISR\index{ISR}), extracts received
-datagrams and dispatches the results to the datagram objects in the
-queue. Received datagrams, and the ones that timed out, will be
-marked, and then dequeued.
-
-\paragraph{Running the Operation State Machine}
-
-The master's operation state machine (see section~\ref{sec:fsm-op})
-monitors the bus in cyclic operation and reconfigures slaves, if
-necessary. Therefore, the following method should be called
-cyclically:
-
-\begin{lstlisting}[language=C]
-  void ecrt_master_run(ec_master_t *master);
-\end{lstlisting}
-
-The \textit{ecrt\_master\_run()} method executes the master's
-operation state machine step by step. It returns after processing one
-state and queuing a datagram. Calling this function is not mandatory,
-but highly recommended.
-
-\paragraph{Master Monitoring}
-
-It is also highly recommended to evaluate the master's error state. In
-this way it is possible to notice lost network links, failed bus
-segments, and other issues:
-
-\begin{lstlisting}[language=C]
-  int ecrt_master_state(const ec_master_t *master);
-\end{lstlisting}
-
-The \textit{ecrt\_master\_state()} method returns the master's error
-state. The following states are defined as part of the realtime
-interface:
-
-\begin{description}
-\item[EC\_MASTER\_OK] means, that no error has occurred.
-\item[EC\_MASTER\_LINK\_ERROR] means, that the network link is
-  currently down.
-\item[EC\_MASTER\_BUS\_ERROR] means, that one or more slaves do not
-  respond.
-\end{description}
-
-\subsubsection{Domain Methods}
-\label{sec:ecrt-domain}
-
-\paragraph{PDO Registration}
-
-To access data of a slave's PDO in cyclic operation, it is necessary
-to make it part of a process data domain:
-
-\begin{lstlisting}[language=C]
-  ec_slave_t *ecrt_domain_register_pdo(ec_domain_t *domain,
-                                       const char *address,
-                                       uint32_t vendor_id,
-                                       uint32_t product_code,
-                                       const char *pdo_name
-                                       void **data_ptr);
-  int ecrt_domain_register_pdo_list(ec_domain_t *domain,
-                                    const ec_pdo_reg_t *pdos);
-\end{lstlisting}
-
-The \textit{ecrt\_domain\_register\_pdo()} method registers a certain
-PDO as part of the domain and takes the address of the process data
-pointer. This pointer will be set on master activation and then can be
-parameter to the \textit{EC\_READ\_*} and \textit{EC\_WRITE\_*} macros
-described below.
-
-A perhaps easier way to register multiple PDOs at the same time is to
-fill an array of \textit{ec\_pdo\_reg\_t} and hand it to the
-\textit{ecrt\_domain\_register\_pdo\_list()} method. Attention: This
-array has to be terminated by an empty structure (\textit{\{\}})!
-
-\paragraph{Evaluating Domain Data}
-
-To evaluate domain data, the following method has to be used:
-
-\begin{lstlisting}[language=C]
-  void ecrt_domain_process(ec_domain_t *domain);
-\end{lstlisting}
-
-The \textit{ecrt\_domain\_process()} method sets the domains state and
-requeues its datagram for sending.
-
-\paragraph{Domain State}
-
-Similar to the master state, a domain has an own error state:
-
-\begin{lstlisting}[language=C]
-  int ecrt_domain_state(const ec_domain_t *domain);
-\end{lstlisting}
-
-The \textit{ecrt\_domain\_state()} method returns the domain's error
-state. It is non-zero if \underline{not} all process data values could
-be exchanged, and zero otherwise.
-
-\subsubsection{Slave Methods}
-\label{sec:ecrt-slave}
-
-\paragraph{SDO Configuration}
-
-To configure slave SDOs, the function interface below can be used:
-
-\begin{lstlisting}[language=C]
-  int ecrt_slave_conf_sdo8(ec_slave_t *slave,
-                           uint16_t sdo_index,
-                           uint8_t sdo_subindex,
-                           uint8_t value);
-  int ecrt_slave_conf_sdo16(ec_slave_t *slave,
-                            uint16_t sdo_index,
-                            uint8_t sdo_subindex,
-                            uint16_t value);
-  int ecrt_slave_conf_sdo32(ec_slave_t *slave,
-                            uint16_t sdo_index,
-                            uint8_t sdo_subindex,
-                            uint32_t value);
-\end{lstlisting}
-
-The \textit{ecrt\_slave\_conf\_sdo*()} methods prepare the
-configuration of a certain SDO. The index and subindex of the SDO, and
-the value have to be specified. The configuration is done each time,
-the slave is reconfigured. The methods only differ in the SDO's data
-type. If the configuration could be prepared, zero is returned. If an
-error occured, non-zero is returned.
-
-\paragraph{Variable-sized PDOs}
-
-For specifying the size of variable-sized PDOs, the following method
-can be used:
-
-\begin{lstlisting}[language=C]
-  int ecrt_slave_pdo_size(ec_slave_t *slave,
-                          const char *pdo_name,
-                          size_t size);
-\end{lstlisting}
-
-The \textit{ecrt\_slave\_pdo\_size()} method takes the name of the PDO
-and the size. It returns zero on success, otherwise non-zero.
-
-\subsubsection{Process Data Access}
-\label{sec:macros}
-
-The endianess of the process data could differ from that of the CPU.
-Therefore, process data access has to be done by the macros below,
-that are also provided by the realtime interface:
-
-\begin{lstlisting}[language=C]
-  #define EC_READ_BIT(DATA, POS)
-  #define EC_WRITE_BIT(DATA, POS, VAL)
-
-  #define EC_READ_U8(DATA)
-  #define EC_READ_S8(DATA)
-  #define EC_READ_U16(DATA)
-  #define EC_READ_S16(DATA)
-  #define EC_READ_U32(DATA)
-  #define EC_READ_S32(DATA)
-
-  #define EC_WRITE_U8(DATA, VAL)
-  #define EC_WRITE_S8(DATA, VAL)
-  #define EC_WRITE_U16(DATA, VAL)
-  #define EC_WRITE_S16(DATA, VAL)
-  #define EC_WRITE_U32(DATA, VAL)
-  #define EC_WRITE_S32(DATA, VAL)
-\end{lstlisting}
-
-There are macros for bitwise access (\textit{EC\_READ\_BIT()},
-\textit{EC\_WRITE\_BIT()}), and bytewise access
-(\textit{EC\_READ\_*()}, \textit{EC\_WRITE\_*()}). The bytewise macros
-carry the data type in their name. Example: \textit{EC\_WRITE\_S16()}
-writes a 16 bit signed value to EtherCAT data. The \textit{DATA}
-parameter is supposed to be a process data pointer, as provided at PDO
-registration.
-
-The macros use the kernel's endianess conversion macros, that are
-preprocessed to empty macros in case of equal endianess. This is the
-definition for the \textit{EC\_\-READ\_\-U16()} macro:
-
-\begin{lstlisting}[language=C]
-  #define EC_READ_U16(DATA) \
-          ((uint16_t) le16_to_cpup((void *) (DATA)))
-\end{lstlisting}
-
-The \textit{le16\_to\_cpup()} macro converts a little-endian, 16 bit
-value to the CPU's architecture and takes a pointer to the input value
-as its argument. If the CPU's architecture is little-endian, too (for
-example on X86 and compatible), nothing has to be converted. In this
-case, the macro is replaced with an empty macro by the preprocessor
-and so there is no unneeded function call or case differentiation in
-the code.
-
-For keeping it portable, it is highly recommended to make use of these
-macros.
-
-%------------------------------------------------------------------------------
-
-\subsection{Slave Addressing}
-\label{sec:addr}
-\index{Slave!Addressing}
-
-The master offers the serveral slave addressing schemes (for PDO
-registration or configuration) via the realtime interface. For this
-reason, slave addresses are ASCII\nomenclature{ASCII}{American
-  Standard Code for Information Interchange}-coded and passed as a
-string. The addressing schemes are independent of the EtherCAT
-protocol and represent an additional feature of the master.
-
-Below, the allowed addressing schemes are described. The descriptions
-are followed by a regular expression formally defining the addressing
-scheme, and one or more examples.
-
-\begin{description}
-\item[Position Addressing] This is the normal addressing scheme, where
-  each slave is addressed by its ring position. The first slave has
-  address 0, and the $n$th slave has address $n - 1$. This addressing
-  scheme is useful for small busses that have a fixed number of slaves.\\
-  RegEx: \texttt{[0-9]+} --- Example: \texttt{"42"}
-\item[Advanced Position Addressing] Bus couplers segment the bus into
-  (physical) blocks. Though the logical ring positions keep being the
-  same, it is easier to address a slave with its block number and the
-  relative position inside the block. This addressing is done by
-  passing the (zero-based) index of the bus coupler (not the coupler's
-  ring position), followed by a colon and the relative position of the
-  actual slave starting at the bus coupler.\\
-  RegEx: \texttt{[0-9]+:[0-9]+} --- Examples: \texttt{"0:42"},
-  \texttt{"2:7"}
-\item[Alias Addressing] Each slave can have a ``secondary slave
-  address'' or ``alias address''\footnote{Information about how to set
-    the alias can be found in section~\ref{sec:eepromaccess}} stored
-  in its E$^2$PROM.  The alias is evaluated by the master and can be
-  used to address the slave, which is useful when a clearly defined
-  slave has to be addressed and the ring position is not known or can
-  change over time. This scheme is used by starting the address string
-  with a mesh (\#) followed by the alias address.  The latter can also
-  be provided as hexadecimal value, prefixed with \textit{0x}.\\
-  RegEx: \texttt{\#(0x[0-9A-F]+|[0-9]+)} --- Examples:
-  \texttt{"\#6622"}, \texttt{"\#0xBEEF"}
-\item[Advanced Alias Addressing] This is a mixture of the ``Alias
-  Addressing'' and ``Advanced Position Addressing'' schemes. A certain
-  slave is addressed by specifying its relative position after an
-  aliased slave. This is very useful, if a complete block of slaves
-  can vary its position in the bus. The bus coupler preceeding the
-  block should get an alias. The block slaves can then be addressed by
-  specifying this alias and their position inside the block. This
-  scheme is used by starting the address string with a mesh (\#)
-  followed by the alias address (which can be hexadecimal), then a
-  colon and the relative posision of the slave to
-  address.\\
-  RegEx: \texttt{\#(0x[0-9A-F]+|[0-9]+):[0-9]+} --- Examples:
-  \texttt{"\#0xBEEF:7"}, \texttt{"\#6:2"}
-\end{description}
-
-In anticipation of section~\ref{sec:ecrt}, the functions accepting
-these address strings are \textit{ecrt\_\-master\_\-get\_slave()},
-\textit{ecrt\_domain\_register\_pdo()} and
-\textit{ecrt\_domain\_register\_pdo\_list()} (the latter through the
-\textit{ec\_pdo\_reg\_t} structure).
-
-%------------------------------------------------------------------------------
-
-\subsection{Concurrent Master Access}
-\label{sec:concurr}
-\index{Concurrency}
-
-In some cases, one master is used by serveral instances, for example
-when a realtime module does cyclic process data exchange, and there
-are EoE-capable slaves that require to exchange Ethernet data with the
-kernel (see section~\ref{sec:eoeimp}). For this reason, the master is
-a shared resource, and access to it has to be sequenctialized. This is
-usually done by locking with semaphores, or other methods to protect
-critical sections.
-
-The master itself can not provide locking mechanisms, because it has
-no chance to know the appropriate kind of lock. Imagine, the realtime
-module uses RTAI functionality, then ordinary kernel semaphores would
-not be sufficient. For that, an important design decision was made:
-The realtime module that reserved a master must have the total
-control, therefore it has to take responsibility for providing the
-appropriate locking mechanisms. If another instance wants to access
-the master, it has to request the master lock by callbacks, that have
-to be set by the realtime module. Moreover the realtime module can
-deny access to the master if it consideres it to be awkward at the
-moment.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.6\textwidth]{images/master-locks}
-  \caption{Concurrent master access}
-  \label{fig:locks}
-\end{figure}
-
-Figure~\ref{fig:locks} exemplary shows, how two processes share one
-master: The realtime module's cyclic thread uses the master for
-process data exchange, while the master-internal EoE process uses it
-to communicate with EoE-capable slaves. Both have to aquire the master
-lock before access: The realtime thread can access the lock natively,
-while the EoE process has to use the master callbacks.
-Section~\ref{sec:concurrency} gives an example, of how to implement
-this.
-
-%------------------------------------------------------------------------------
-
-\section{The Master's State Machines}
-\label{sec:fsm}
-\index{FSM}
-
-Many parts of the EtherCAT master are implemented as \textit{finite
-  state machines} (FSMs\nomenclature{FSM}{Finite State Machine}).
-Though this leads to a higher grade of complexity in some aspects, is
-opens many new possibilities.
-
-The below short code example exemplary shows how to read all slave
-states and moreover illustrates the restrictions of ``sequential''
-coding:
-
-\begin{lstlisting}[language=C,numbers=left]
-  ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram
-  if (ec_master_simple_io(master, datagram)) return -1;
-  slave_states = EC_READ_U8(datagram->data); // process datagram
-\end{lstlisting}
-
-The \textit{ec\_master\_simple\_io()} function provides a simple
-interface for synchronously sending a single datagram and receiving
-the result\footnote{For all communication issues have been meanwhile
-  sourced out into state machines, the function is deprecated and
-  stopped existing. Nevertheless it is adequate for showing it's own
-  restrictions.}. Internally, it queues the specified datagram,
-invokes the \textit{ec\_master\_send\_datagrams()} function to send a
-frame with the queued datagram and then waits actively for its
-reception.
-
-This sequential approach is very simple, reflecting in only three
-lines of code. The disadvantage is, that the master is blocked for the
-time it waits for datagram reception. There is no difficulty when only
-one instance is using the master, but if more instances want to
-(synchronously\footnote{At this time, synchronous master access will
-  be adequate to show the advantages of an FSM. The asynchronous
-  approach will be discussed in section~\ref{sec:eoeimp}}) use the
-master, it is inevitable to think about an alternative to the
-sequential model.
-
-Master access has to be sequentialized for more than one instance
-wanting to send and receive datagrams synchronously. With the present
-approach, this would result in having one phase of active waiting for
-each instance, which would be non-acceptable especially in realtime
-circumstances, because of the huge time overhead.
-
-A possible solution is, that all instances would be executed
-sequentially to queue their datagrams, then give the control to the
-next instance instead of waiting for the datagram reception. Finally,
-bus IO is done by a higher instance, which means that all queued
-datagrams are sent and received. The next step is to execute all
-instances again, which then process their received datagrams and issue
-new ones.
-
-This approach results in all instances having to retain their state,
-when giving the control back to the higher instance. It is quite
-obvious to use a \textit{finite state machine} model in this case.
-Section~\ref{sec:fsmtheory} will introduce some of the theory used,
-while the listings below show the basic approach by coding the example
-from above as a state machine:
-
-\begin{lstlisting}[language=C,numbers=left]
-  // state 1
-  ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram
-  ec_master_queue(master, datagram); // queue datagram
-  next_state = state_2;
-  // state processing finished
-\end{lstlisting}
-
-After all instances executed their current state and queued their
-datagrams, these are sent and received. Then the respective next
-states are executed:
-
-\begin{lstlisting}[language=C,numbers=left]
-  // state 2
-  if (datagram->state != EC_DGRAM_STATE_RECEIVED) {
-          next_state = state_error;
-          return; // state processing finished
-  }
-  slave_states = EC_READ_U8(datagram->data); // process datagram
-  // state processing finished.
-\end{lstlisting}
-
-See section~\ref{sec:statemodel} for an introduction to the
-state machine programming concept used in the master code.
-
-%------------------------------------------------------------------------------
-
-\subsection{State Machine Theory}
-\label{sec:fsmtheory}
-\index{FSM!Theory}
-
-A finite state machine \cite{automata} is a model of behavior with
-inputs and outputs, where the outputs not only depend on the inputs,
-but the history of inputs. The mathematical definition of a finite
-state machine (or finite automaton) is a six-tuple $(\Sigma, \Gamma,
-S, s_0, \delta, \omega)$, with
-
-\begin{itemize}
-\item the input alphabet $\Sigma$, with $\Sigma \neq
-  \emptyset$, containing all input symbols,
-\item the output alphabet $\Gamma$, with $\Gamma \neq
-  \emptyset$, containing all output symbols,
-\item the set of states $S$, with $S \neq \emptyset$,
-\item the set of initial states $s_0$ with $s_0 \subseteq S, s_0 \neq
-  \emptyset$
-\item the transition function $\delta: S \times \Sigma \rightarrow S
-  \times \Gamma$
-\item the output function $\omega$.
-\end{itemize}
-
-The state transition function $\delta$ is often specified by a
-\textit{state transition table}, or by a \textit{state transition
-  diagram}. The transition table offers a matrix view of the state
-machine behavior (see table~\ref{tab:statetrans}). The matrix rows
-correspond to the states ($S = \{s_0, s_1, s_2\}$) and the columns
-correspond to the input symbols ($\Gamma = \{a, b, \varepsilon\}$).
-The table contents in a certain row $i$ and column $j$ then represent
-the next state (and possibly the output) for the case, that a certain
-input symbol $\sigma_j$ is read in the state $s_i$.
-
-\begin{table}[htbp]
-  \caption{A typical state transition table}
-  \label{tab:statetrans}
-  \vspace{2mm}
-  \centering
-  \begin{tabular}{l|ccc}
-    & $a$ & $b$ & $\varepsilon$\\ \hline
-    $s_0$ & $s_1$ & $s_1$ & $s_2$\\
-    $s_1$ & $s_2$ & $s_1$ & $s_0$\\
-    $s_2$ & $s_0$ & $s_0$ & $s_0$\\ \hline
-  \end{tabular}
-\end{table}
-
-The state diagram for the same example looks like the one in
-figure~\ref{fig:statetrans}. The states are represented as circles or
-ellipses and the transitions are drawn as arrows between them. Close
-to a transition arrow can be the condition that must be fulfilled to
-allow the transition. The initial state is marked by a filled black
-circle with an arrow pointing to the respective state.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.5\textwidth]{images/statetrans}
-  \caption{A typical state transition diagram}
-  \label{fig:statetrans}
-\end{figure}
-
-\paragraph{Deterministic and non-deterministic state machines}
-
-A state machine can be deterministic, meaning that for one state and
-input, there is one (and only one) following state. In this case, the
-state machine has exactly one starting state. Non-deterministic state
-machines can have more than one transitions for a single state-input
-combination. There is a set of starting states in the latter case.
-
-\paragraph{Moore and Mealy machines}
-
-There is a distinction between so-called \textit{Moore machines}, and
-\textit{Mealy machines}. Mathematically spoken, the distinction lies
-in the output function $\omega$: If it only depends on the current
-state ($\omega: S \rightarrow \Gamma$), the machine corresponds to the
-``Moore Model''. Otherwise, if $\omega$ is a function of a state and
-the input alphabet ($\omega: S \times \Sigma \rightarrow \Gamma$) the
-state machine corresponds to the ``Mealy model''. Mealy machines are
-the more practical solution in most cases, because their design allows
-machines with a minimum number of states. In practice, a mixture of
-both models is often used.
-
-\paragraph{Misunderstandings about state machines}
-
-There is a phenomenon called ``state explosion'', that is oftenly
-taken as a counter-argument against general use of state machines in
-complex environments. It has to be mentioned, that this point is
-misleading~\cite{fsmmis}. State explosions happen usually as a result
-of a bad state machine design: Common mistakes are storing the present
-values of all inputs in a state, or not dividing a complex state
-machine into simpler sub state machines. The EtherCAT master uses
-serveral state machines, that are executed hierarchically and so serve
-as sub state machines. These are also described below.
-
-%------------------------------------------------------------------------------
-
-\subsection{The Master's State Model}
-\label{sec:statemodel}
-
-This section will introduce the techniques used in the master to
-implement state machines.
-
-\paragraph{State Machine Programming}
-
-There are certain ways to implement a state machine in \textit{C}
-code. An obvious way is to implement the different states and actions
-by one big case differentiation:
-
-\begin{lstlisting}[language=C,numbers=left]
-  enum {STATE_1, STATE_2, STATE_3};
-  int state = STATE_1;
-
-  void state_machine_run(void *priv_data) {
-          switch (state) {
-                  case STATE_1:
-                          action_1();
-                          state = STATE_2;
-                          break;
-                  case STATE_2:
-                          action_2()
-                          if (some_condition) state = STATE_1;
-                          else state = STATE_3;
-                          break;
-                  case STATE_3:
-                          action_3();
-                          state = STATE_1;
-                          break;
-          }
-  }
-\end{lstlisting}
-
-For small state machines, this is an option. The disadvantage is, that
-with an increasing number of states the code soon gets complex and an
-additional case differentiation is executed each run. Besides, lots of
-indentation is wasted.
-
-The method used in the master is to implement every state in an own
-function and to store the current state function with a function
-pointer:
-
-\begin{lstlisting}[language=C,numbers=left]
-  void (*state)(void *) = state1;
-
-  void state_machine_run(void *priv_data) {
-          state(priv_data);
-  }
-
-  void state1(void *priv_data) {
-          action_1();
-          state = state2;
-  }
-
-  void state2(void *priv_data) {
-          action_2();
-          if (some_condition) state = state1;
-          else state = state2;
-  }
-
-  void state3(void *priv_data) {
-          action_3();
-          state = state1;
-  }
-\end{lstlisting}
-
-In the master code, state pointers of all state machines\footnote{All
-  except for the EoE state machine, because multiple EoE slaves have
-  to be handled in parallel. For this reason each EoE handler object
-  has its own state pointer.} are gathered in a single object of the
-\textit{ec\_fsm\_t} class. This is advantageous, because there is
-always one instance of every state machine available and can be
-started on demand.
-
-\paragraph{Mealy and Moore}
-
-If a closer look is taken to the above listing, it can be seen that
-the actions executed (the ``outputs'' of the state machine) only
-depend on the current state. This accords to the ``Moore'' model
-introduced in section~\ref{sec:fsmtheory}. As mentioned, the ``Mealy''
-model offers a higher flexibility, which can be seen in the listing
-below:
-
-\begin{lstlisting}[language=C,numbers=left]
-  void state7(void *priv_data) {
-          if (some_condition) {
-                  action_7a();
-                  state = state1;
-          }
-          else {
-                  action_7b();
-                  state = state8;
-          }
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3} + \textcircled{\tiny 7}] The
-  state function executes the actions depending on the state
-  transition, that is about to be done.
-\end{description}
-
-The most flexible alternative is to execute certain actions depending
-on the state, followed by some actions dependent on the state
-transition:
-
-\begin{lstlisting}[language=C,numbers=left]
-  void state9(void *priv_data) {
-          action_9();
-          if (some_condition) {
-                  action_9a();
-                  state = state7;
-          }
-          else {
-                  action_9b();
-                  state = state10;
-          }
-  }
-\end{lstlisting}
-
-This model is oftenly used in the master. It combines the best aspects
-of both approaches.
-
-\paragraph{Using Sub State Machines}
-
-To avoid having too much states, certain functions of the EtherCAT
-master state machine have been sourced out into sub state machines.
-This helps to encapsule the related workflows and moreover avoids the
-``state explosion'' phenomenon described in
-section~\ref{sec:fsmtheory}. If the master would instead use one big
-state machine, the number of states would be a multiple of the actual
-number. This would increase the level of complexity to a
-non-manageable grade.
-
-\paragraph{Executing Sub State Machines}
-
-If a state machine starts to execute a sub state machine, it usually
-remains in one state until the sub state machine terminates. This is
-usually done like in the listing below, which is taken out of the
-slave configuration state machine code:
-
-\begin{lstlisting}[language=C,numbers=left]
-  void ec_fsm_slaveconf_saveop(ec_fsm_t *fsm)
-  {
-          fsm->change_state(fsm); // execute state change
-                                  // sub state machine
-
-          if (fsm->change_state == ec_fsm_error) {
-                  fsm->slave_state = ec_fsm_end;
-                  return;
-          }
-
-          if (fsm->change_state != ec_fsm_end) return;
-
-          // continue state processing
-          ...
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] \textit{change\_state} is the
-  state pointer of the state change state machine. The state function,
-  the pointer points on, is executed\ldots
-\item[\normalfont\textcircled{\tiny 6}] \ldots either until the state
-  machine terminates with the error state \ldots
-\item[\normalfont\textcircled{\tiny 11}] \ldots or until the state
-  machine terminates in the end state. Until then, the ``higher''
-  state machine remains in the current state and executes the sub
-  state machine again in the next cycle.
-\end{description}
-
-\paragraph{State Machine Descriptions}
-
-The below sections describe every state machine used in the EtherCAT
-master. The textual descriptions of the state machines contain
-references to the transitions in the corresponding state transition
-diagrams, that are marked with an arrow followed by the name of the
-successive state.  Transitions caused by trivial error cases (i.~e. no
-response from slave) are not described explicitly. These transitions
-are drawn as dashed arrows in the diagrams.
-
-%------------------------------------------------------------------------------
-
-\subsection{The Operation State Machine}
-\label{sec:fsm-op}
-\index{FSM!Operation}
-
-The Operation state machine is executed by calling the
-\textit{ecrt\_master\_run()} method in cyclic realtime code. Its
-purpose is to monitor the bus and to reconfigure slaves after a bus
-failure or power failure. Figure~\ref{fig:fsm-op} shows its transition
-diagram.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.8\textwidth]{images/fsm-op}
-  \caption{Transition diagram of the operation state machine}
-  \label{fig:fsm-op}
-\end{figure}
-
-\begin{description}
-\item[START] This is the beginning state of the operation state
-  machine. There is a datagram issued, that queries the ``AL Control
-  Response'' attribute \cite[section~5.3.2]{alspec} of all slaves via
-  broadcast. In this way, all slave states and the number of slaves
-  responding can be determined.  $\rightarrow$~\textit{BROADCAST}
-
-\item[BROADCAST] The broadcast datagram is evaluated. A change in the
-  number of responding slaves is treates as a topology change. If the
-  number of slaves is not as expected, the bus is marked as
-  ``tainted''. In this state, no slave reconfiguration is possible,
-  because the assignment of known slaves and those present on the bus
-  is ambiguous. If the number of slaves is considered as right, the
-  bus is marked for validation, because it turned from tainted to
-  normal state and it has to be checked, if all slaves are valid. Now,
-  the state of every single slave has to be determined. For that, a
-  (unicast) datagram is issued, that queries the first slave's ``AL
-  Control Response'' attribute. $\rightarrow$~\textit{READ STATES}
-
-\item[READ STATES] If the current slave did not respond to its
-  configured station address, it is marked as offline, and the next
-  slave is queried. $\rightarrow$~\textit{READ STATES}
-
-  If the slave responded, it is marked as online and its current state
-  is stored. The next slave is queried. $\rightarrow$~\textit{READ
-    STATES}
-
-  If all slaves have been queried, and the bus is marked for
-  validation, the validation is started by checking the first slaves
-  vendor ID. $\rightarrow$~\textit{VALIDATE VENDOR}
-
-  If no validation has to be done, it is checked, if all slaves are in
-  the state they are supposed to be. If not, the first of slave with
-  the wrong state is reconfigured and brought in the required state.
-  $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  If all slaves are in the correct state, the state machine is
-  restarted. $\rightarrow$~\textit{START}
-
-\item[CONFIGURE SLAVES] The slave configuration state machine is
-  executed until termination. $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  If there are still slaves in the wrong state after another check,
-  the first of these slaves is configured and brought into the correct
-  state again. $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  If all slaves are in the correct state, the state machine is
-  restarted. $\rightarrow$~\textit{START}
-
-\item[VALIDATE VENDOR] The SII state machine is executed until
-  termination. If the slave has the wrong vendor ID, the state machine
-  is restarted. $\rightarrow$~\textit{START}
-
-  If the slave has the correct vendor ID, its product ID is queried.
-  $\rightarrow$~\textit{VALIDATE PRODUCT}
-
-\item[VALIDATE PRODUCT] The SII state machine is executed until
-  termination. If the slave has the wrong product ID, the state
-  machine is restarted. $\rightarrow$~\textit{START}
-
-  If the slave has the correct product ID, the next slave's vendor ID
-  is queried. $\rightarrow$~\textit{VALIDATE VENDOR}
-
-  If all slaves have the correct vendor IDs and product codes, the
-  configured station addresses can be safely rewritten. This is done
-  for the first slave marked as offline.
-  $\rightarrow$~\textit{REWRITE ADDRESSES}
-
-\item[REWRITE ADDRESSES] If the station address was successfully
-  written, it is sear\-ched for the next slave marked as offline. If
-  there is one, its address is reconfigured, too.
-  $\rightarrow$~\textit{REWRITE ADDRESSES}
-
-  If there are no more slaves marked as offline, the state machine is
-  restarted. $\rightarrow$~\textit{START}
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The Idle State Machine}
-\label{sec:fsm-idle}
-\index{FSM!Idle}
-
-The Idle state machine is executed by a kernel workqueue, if no
-realtime module is connected. Its purpose is to make slave information
-available to user space, operate EoE-capable slaves, read and write
-E$^2$PROM contents and test slave functionality.
-Figure~\ref{fig:fsm-idle} shows its transition diagram.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.8\textwidth]{images/fsm-idle}
-  \caption{Transition diagram of the idle state machine}
-  \label{fig:fsm-idle}
-\end{figure}
-
-\begin{description}
-\item[START] The beginning state of the idle state machine. Similar to
-  the operation state machine, a broadcast datagram is issued, to
-  query all slave states and the number of slaves.
-  $\rightarrow$~\textit{BROADCAST}
-
-\item[BROADCAST] The number of responding slaves is evaluated. If it
-  has changed since the last time, this is treated as a topology
-  change and the internal list of slaves is cleared and rebuild
-  completely. The slave scan state machine is started for the first
-  slave. $\rightarrow$~\textit{SCAN FOR SLAVES}
-
-  If no topology change happened, every single slave state is fetched.
-  $\rightarrow$~\textit{READ STATES}
-
-\item[SCAN FOR SLAVES] The slave scan state machine is executed until
-  termination. $\rightarrow$~\textit{SCAN FOR SLAVES}
-
-  If there is another slave to scan, the slave scan state machine is
-  started again. $\rightarrow$~\textit{SCAN FOR SLAVES}
-
-  If all slave information has been fetched, slave addresses are
-  calculated and EoE processing is started. Then, the state machine is
-  restarted. $\rightarrow$~\textit{START}
-
-\item[READ STATES] If the slave did not respond to the query, it is
-  marked as offline. The next slave is queried.
-  $\rightarrow$~\textit{READ STATES}
-
-  If the slave responded, it is marked as online. And the next slave
-  is queried. $\rightarrow$~\textit{READ STATES}
-
-  If all slave states have been determined, it is checked, if any
-  slaves are not in the state they supposed to be. If this is true,
-  the slave configuration state machine is started for the first of
-  them. $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  If all slaves are in the correct state, it is checked, if any
-  E$^2$PROM write operations are pending. If this is true, the first
-  pending operation is executed by starting the SII state machine for
-  writing access. $\rightarrow$~\textit{WRITE EEPROM}
-
-  If all these conditions are false, there is nothing to do and the
-  state machine is restarted. $\rightarrow$~\textit{START}
-
-\item[CONFIGURE SLAVES] The slave configuration state machine is
-  executed until termination. $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  After this, it is checked, if another slave needs a state change. If
-  this is true, the slave state change state machine is started for
-  this slave. $\rightarrow$~\textit{CONFIGURE SLAVES}
-
-  If all slaves are in the correct state, it is determined, if any
-  E$^2$PROM write operations are pending. If this is true, the first
-  pending operation is executed by starting the SII state machine for
-  writing access. $\rightarrow$~\textit{WRITE EEPROM}
-
-  If all prior conditions are false, the state machine is restarted.
-  $\rightarrow$~\textit{START}
-
-\item[WRITE EEPROM] The SII state machine is executed until
-  termination. $\rightarrow$~\textit{WRITE EEPROM}
-
-  If the current word has been written successfully, and there are
-  still word to write, the SII state machine is started for the next
-  word. $\rightarrow$~\textit{WRITE EEPROM}
-
-  If all words have been written successfully, the new E$^2$PROM
-  contents are evaluated and the state machine is restarted.
-  $\rightarrow$~\textit{START}
-
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The Slave Scan State Machine}
-\label{sec:fsm-scan}
-\index{FSM!Slave Scan}
-
-The slave scan state machine, which can be seen in
-figure~\ref{fig:fsm-slavescan}, leads through the process of fetching
-all slave information.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.6\textwidth]{images/fsm-slavescan}
-  \caption{Transition diagram of the slave scan state machine}
-  \label{fig:fsm-slavescan}
-\end{figure}
-
-\begin{description}
-\item[START] In the beginning state of the slave scan state machine,
-  the station address is written to the slave, which is always the
-  ring position~+~$1$. In this way, the address 0x0000 (default
-  address) is not used, which makes it easy to detect unconfigured
-  slaves.  $\rightarrow$~\textit{ADDRESS}
-
-\item[ADDRESS] The writing of the station address is verified. After
-  that, the slave's ``AL Control Response'' attribute is queried.
-  $\rightarrow$~\textit{STATE}
-
-\item[STATE] The AL state is evaluated. A warning is output, if the
-  slave has still the \textit{Change} bit set. After that, the slave's
-  ``DL Information'' attribute is queried.
-  $\rightarrow$~\textit{BASE}
-
-\item[BASE] The queried base data are evaluated: Slave type, revision
-  and build number, and even more important, the number of supported
-  sync managers and FMMUs are stored. After that, the slave's data
-  link layer information is read from the ``DL Status'' attribute at
-  address 0x0110. $\rightarrow$~\textit{DATALINK}
-
-\item[DATALINK] In this state, the DL information is evaluated: This
-  information about the communication ports contains, if the link is
-  up, if the loop has been closed and if there is a carrier detected
-  on the RX side of each port.
-
-  Then, the state machine starts measuring the size of the slave's
-  E$^2$PROM contents. This is done by subsequently reading out each
-  category header, until the last category is reached (type 0xFFFF).
-  This procedure is started by querying the first category header at
-  word address 0x0040 via the SII state machine.
-  $\rightarrow$~\textit{EEPROM SIZE}
-
-\item[EEPROM SIZE] The SII state machine is executed until
-  termination. $\rightarrow$~\textit{EEPROM SIZE}
-
-  If the category type does not mark the end of the categories, the
-  position of the next category header is determined via the length of
-  the current category, and the SII state machine is started again.
-  $\rightarrow$~\textit{EEPROM SIZE}
-
-  If the size of the E$^2$PROM contents has been determined, memory is
-  allocated, to read all the contents. The SII state machine is
-  started to read the first word. $\rightarrow$~\textit{EEPROM DATA}
-
-\item[EEPROM DATA] The SII state machine is executed until
-  termination. $\rightarrow$~\textit{EEPROM DATA}
-
-  Two words have been read. If more than one word is needed, the two
-  words are written in the allocated memory. Otherwise only one word
-  (the last word) is copied. If more words are to read, the SII state
-  machine is started again to read the next two words.
-  $\rightarrow$~\textit{EEPROM DATA}
-
-  The complete E$^2$PROM contents have been read. The slave's identity
-  object and mailbox information are evaluated. Moreover the category
-  types STRINGS, GENERAL, SYNC and PDO are evaluated. The slave
-  scanning has been completed. $\rightarrow$~\textit{END}
-
-\item[END] Slave scanning has been finished.
-
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The Slave Configuration State Machine}
-\label{sec:fsm-conf}
-\index{FSM!Slave Configuration}
-
-The slave configuration state machine, which can be seen in
-figure~\ref{fig:fsm-slaveconf}, leads through the process of
-configuring a slave and bringing it to a certain state.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.6\textwidth]{images/fsm-slaveconf}
-  \caption{Transition diagram of the slave configuration state
-    machine}
-  \label{fig:fsm-slaveconf}
-\end{figure}
-
-\begin{description}
-\item[INIT] The state change state machine has been initialized to
-  bring the slave into the \textit{INIT} state. Now, the slave state
-  change state machine is executed until termination.
-  $\rightarrow$~\textit{INIT}
-
-  If the slave state change failed, the configuration has to be
-  aborted. $\rightarrow$~\textit{END}
-
-  The slave state change succeeded and the slave is now in
-  \textit{INIT} state. If this is the target state, the configuration
-  is finished. $\rightarrow$~\textit{END}
-
-  If the slave does not support any sync managers, the sync manager
-  configuration can be skipped. The state change state machine is
-  started to bring the slave into \textit{PREOP} state.
-  $\rightarrow$~\textit{PREOP}
-
-  Sync managers are configured conforming to the sync manager category
-  information provided in the slave's E$^2$PROM. The corresponding
-  datagram is issued. $\rightarrow$~\textit{SYNC}
-
-\item[SYNC] If the sync manager configuration datagram is accepted,
-  the sync manager configuration was successful. The slave may now
-  enter the \textit{PREOP} state, and the state change state machine
-  is started. $\rightarrow$~\textit{PREOP}
-
-\item[PREOP] The state change state machine is executed until
-  termination. $\rightarrow$~\textit{PREOP}
-
-  If the state change failed, the configuration has to be aborted.
-  $\rightarrow$~\textit{END}
-
-  If the \textit{PREOP} state was the target state, the configuration
-  is finished. $\rightarrow$~\textit{END}
-
-  If the slave supports no FMMUs, the FMMU configuration can be
-  skipped. If the slave has SDOs to configure, it is begun with
-  sending the first SDO. $\rightarrow$~\textit{SDO\_CONF}
-
-  If no SDO configurations are provided, the slave can now directly be
-  brought into the \textit{SAVEOP} state and the state change state
-  machine is started again. $\rightarrow$~\textit{SAVEOP}
-
-  Otherwise, all supported FMMUs are configured according to the PDOs
-  requested via the master's realtime interface. The appropriate
-  datagram is issued. $\rightarrow$~\textit{FMMU}
-
-\item[FMMU] The FMMU configuration datagram was accepted. If the slave
-  has SDOs to configure, it is begun with sending the first SDO.
-  $\rightarrow$~\textit{SDO\_CONF}
-
-  Otherwise, the slave can now be brought into the \textit{SAVEOP}
-  state. The state change state machine is started.
-  $\rightarrow$~\textit{SAVEOP}
-
-\item[SDO\_CONF] The CoE state machine is executed until termination.
-  $\rightarrow$~\textit{SDO\_CONF}
-
-  If another SDO has to be configured, a new SDO download sequence is
-  begun. $\rightarrow$~\textit{SDO\_CONF}
-
-  Otherwise, the slave can now be brought into the \textit{SAVEOP}
-  state. The state change state machine is started.
-  $\rightarrow$~\textit{SAVEOP}
-
-\item[SAVEOP] The state change state machine is executed until
-  termination. $\rightarrow$~\textit{SAVEOP}
-
-  If the state change failed, the configuration has to be aborted.
-  $\rightarrow$~\textit{END}
-
-  If the \textit{SAVEOP} state was the target state, the configuration
-  is finished. $\rightarrow$~\textit{END}
-
-  The slave can now directly be brought into the \textit{OP} state and
-  the state change state machine is started a last time.
-  $\rightarrow$~\textit{OP}
-
-\item[OP] The state change state machine is executed until
-  termination. $\rightarrow$~\textit{OP}
-
-  If the state change state machine terminates, the slave
-  configuration is finished, regardless of its success.
-  $\rightarrow$~\textit{END}
-
-\item[END] The termination state.
-
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The State Change State Machine}
-\label{sec:fsm-change}
-\index{FSM!State Change}
-
-The state change state machine, which can be seen in
-figure~\ref{fig:fsm-change}, leads through the process of changing a
-slave's state. This implements the states and transitions described in
-\cite[section~6.4.1]{alspec}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/fsm-change}
-  \caption{Transition diagram of the state change state machine}
-  \label{fig:fsm-change}
-\end{figure}
-
-\begin{description}
-\item[START] The beginning state, where a datagram with the state
-  change command is written to the slave's ``AL Control Request''
-  attribute. Nothing can fail. $\rightarrow$~\textit{CHECK}
-
-\item[CHECK] After the state change datagram has been sent, the ``AL
-  Control Response'' attribute is queried with a second datagram.
-  $\rightarrow$~\textit{STATUS}
-
-\item[STATUS] The read memory contents are evaluated: While the
-  parameter \textit{State} still contains the old slave state, the
-  slave is busy with reacting on the state change command. In this
-  case, the attribute has to be queried again.
-  $\rightarrow$~\textit{STATUS}
-
-  In case of success, the \textit{State} parameter contains the new
-  state and the \textit{Change} bit is cleared. The slave is in the
-  requested state.  $\rightarrow$~\textit{END}
-
-  If the slave can not process the state change, the \textit{Change}
-  bit is set: Now the master tries to get the reason for this by
-  querying the \textit{AL Status Code} parameter.
-  $\rightarrow$~\textit{CODE}
-
-\item[END] If the state machine ends in this state, the slaves's state
-  change has been successful.
-
-\item[CODE] The status code query has been sent. Reading the
-  \textit{AL Status Code} might fail, because not all slaves support
-  this parameter. Anyway, the master has to acknowledge the state
-  change error by writing the current slave state to the ``AL Control
-  Request'' attribute with the \textit{Acknowledge} bit set.
-  $\rightarrow$~\textit{ACK}
-
-\item[ACK] After that, the ``AL Control Response'' attribute is
-  queried for the state of the acknowledgement.
-  $\rightarrow$~\textit{CHECK ACK}
-
-\item[CHECK ACK] If the acknowledgement has been accepted by the
-  slave, the old state is kept. Still, the state change was
-  unsuccessful. $\rightarrow$~\textit{ERROR}
-
-  If the acknowledgement is ignored by the slave, a timeout happens.
-  In any case, the overall state change was unsuccessful.
-  $\rightarrow$~\textit{ERROR}
-
-  If there is still now response from the slave, but the timer did not
-  run out yet, the slave's ``AL Control Response'' attribute is
-  queried again.  $\rightarrow$~\textit{CHECK ACK}
-
-\item[ERROR] If the state machine ends in this state, the slave's
-  state change was unsuccessful.
-
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{The SII State Machine}
-\label{sec:fsm-sii}
-\index{FSM!SII}
-
-The SII\index{SII} state machine (shown in figure~\ref{fig:fsm-sii})
-implements the process of reading or writing E$^2$PROM data via the
-Slave Information Interface described in \cite[section~5.4]{alspec}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/fsm-sii}
-  \caption{Transition diagram of the SII state machine}
-  \label{fig:fsm-sii}
-\end{figure}
-
-\begin{description}
-\item[READ\_START] The beginning state for reading access, where the
-  read request and the requested address are written to the SII
-  attribute. Nothing can fail up to now.
-  $\rightarrow$~\textit{READ\_CHECK}
-
-\item[READ\_CHECK] When the SII read request has been sent
-  successfully, a timer is started. A check/fetch datagram is issued,
-  that reads out the SII attribute for state and data.
-  $\rightarrow$~\textit{READ\_FETCH}
-
-\item[READ\_FETCH] Upon reception of the check/fetch datagram, the
-  \textit{Read Operation} and \textit{Busy} parameters are checked:
-  \begin{itemize}
-  \item If the slave is still busy with fetching E$^2$PROM data into
-    the interface, the timer is checked. If it timed out, the reading
-    is aborted ($\rightarrow$~\textit{ERROR}), if not, the check/fetch
-    datagram is issued again. $\rightarrow$~\textit{READ\_FETCH}
-
-  \item If the slave is ready with reading data, these are copied from
-    the datagram and the read cycle is completed.
-    $\rightarrow$~\textit{END}
-  \end{itemize}
-\end{description}
-
-The write access states behave nearly the same:
-
-\begin{description}
-\item[WRITE\_START] The beginning state for writing access,
-  respectively. A write request, the target address and the data word
-  are written to the SII attribute. Nothing can fail.
-  $\rightarrow$~\textit{WRITE\_CHECK}
-
-\item[WRITE\_CHECK] When the SII write request has been sent
-  successfully, the timer is started. A check datagram is issued, that
-  reads out the SII attribute for the state of the write operation.
-  $\rightarrow$~\textit{WRITE\_CHECK2}
-
-\item[WRITE\_CHECK2] Upon reception of the check datagram, the
-  \textit{Write Operation} and \textit{Busy} parameters are checked:
-  \begin{itemize}
-  \item If the slave is still busy with writing E$^2$PROM data, the
-    timer is checked. If it timed out, the operation is aborted
-    ($\rightarrow$~\textit{ERROR}), if not, the check datagram is
-    issued again. $\rightarrow$~\textit{WRITE\_CHECK2}
-  \item If the slave is ready with writing data, the write cycle is
-    completed. $\rightarrow$~\textit{END}
-  \end{itemize}
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{Mailbox Protocol Implementations}
-\index{Mailbox}
-
-The EtherCAT master implements the EoE and the CoE mailbox
-protocols. See the below section for details.
-
-%------------------------------------------------------------------------------
-
-\subsection{Ethernet-over-EtherCAT (EoE)}
-\label{sec:eoeimp}
-\index{EoE}
-
-The EtherCAT master implements the Ethernet-over-EtherCAT mailbox
-protocol to enable the tunneling of Ethernet frames to special slaves,
-that can either have physical Ethernet ports to forward the frames to,
-or have an own IP stack to receive the frames.
-
-\paragraph{Virtual Network Interfaces}
-
-The master creates a virtual EoE network interface for every
-EoE-capable slave. These interfaces are called \textit{eoeX}, where X
-is a number provided by the kernel on interface registration. Frames
-sent to these interfaces are forwarded to the associated slaves by the
-master. Frames, that are received by the slaves, are fetched by the
-master and forwarded to the virtual interfaces.
-
-This bears the following advantages:
-
-\begin{itemize}
-\item Flexibility: The user can decide, how the EoE-capable slaves are
-  interconnected with the rest of the world.
-\item Standard tools can be used to monitor the EoE activity and to
-  configure the EoE interfaces.
-\item The Linux kernel's layer-2-bridging implementation (according to
-  the IEEE 802.1D MAC Bridging standard) can be used natively to
-  bridge Ethernet traffic between EoE-capable slaves.
-\item The Linux kernel's network stack can be used to route packets
-  between EoE-capable slaves and to track security issues, just like
-  having physical network interfaces.
-\end{itemize}
-
-\paragraph{EoE Handlers}
-
-The virtual EoE interfaces and the related functionality is encapsuled
-in the \textit{ec\_eoe\_t} class (see section~\ref{sec:class-eoe}).
-So the master does not create the network interfaces directly: This is
-done inside the constructor of the \textit{ec\_eoe\_t} class. An
-object of this class is called ``EoE handler'' below. An EoE handler
-additionaly contains a frame queue. Each time, the kernel passes a new
-socket buffer for sending via the interface's
-\textit{hard\_start\_xmit()} callback, the socket buffer is queued for
-transmittion by the EoE state machine (see below). If the queue gets
-filled up, the passing of new socket buffers is suspended with a call
-to \textit{netif\_stop\_queue()}.
-
-\paragraph{Static Handler Creation}
-
-The master creates a pool of EoE handlers at startup, that are coupled
-to EoE-capable slaves on demand. The lifetime of the corresponding
-network interfaces is equal to the lifetime of the master module.
-This approach is opposed to creating the virtual network interfaces on
-demand (i.~e. on running across a new EoE-capable slave). The latter
-approach was considered as difficult, because of serveral reasons:
-
-\begin{itemize}
-\item The \textit{alloc\_netdev()} function can sleep and must be
-  called from a non-interrupt context. This reduces the flexibility of
-  choosing an appropriate method for cyclic EoE processing.
-\item Unregistering network interfaces requires them to be ``down'',
-  which can not be guaranteed upon sudden disappearing of an
-  EoE-capable slave.
-\item The connection to the EoE-capable slaves must be as continuous
-  as possible. Especially the transition from idle to operation mode
-  (and vice versa) causes the rebuilding of the internal data
-  structures. These transitions must be as transparent as possible for
-  the instances using the network interfaces.
-\end{itemize}
-
-\paragraph{Number of Handlers}
-
-The master module has a parameter \textit{ec\_eoeif\_count} to specify
-the number of EoE interfaces (and handlers) per master to create. This
-parameter can either be specified when manually loading the master
-module, or (when using the init script) by setting the
-\textit{\$EOE\_INTERFACES} variable in the sysconfig file (see
-section~\ref{sec:sysconfig}). Upon loading of the master module, the
-virtual interfaces become available:
-
-\begin{lstlisting}
-  host# `\textbf{ifconfig -a}`
-  eoe0      Link encap:Ethernet  HWaddr 00:11:22:33:44:06
-            BROADCAST MULTICAST  MTU:1500  Metric:1
-            RX packets:0 errors:0 dropped:0 overruns:0 frame:0
-            TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
-            collisions:0 txqueuelen:1000
-            RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
-
-  eoe1      Link encap:Ethernet  HWaddr 00:11:22:33:44:07
-            BROADCAST MULTICAST  MTU:1500  Metric:1
-            RX packets:0 errors:0 dropped:0 overruns:0 frame:0
-            TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
-            collisions:0 txqueuelen:1000
-            RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
-  ...
-\end{lstlisting}
-
-\paragraph{Coupling of EoE Slaves}
-
-During execution of the slave scan state machine (see
-section~\ref{sec:fsm-scan}), the master determines the supported
-mailbox protocols. This is done by examining the ``Supported Mailbox
-Protocols'' mask field at word address 0x001C of the SII\index{SII}.
-If bit 1 is set, the slave supports the EoE protocol. After slave
-scanning, the master runs through all slaves again and couples each
-EoE-capable slave to a free EoE handler. It can happen, that there are
-not enough EoE handlers to cover all EoE-capable slaves. In this case,
-the number of EoE handlers must be increased accordingly.
-
-\paragraph{EoE State Machine}
-\index{FSM!EoE}
-
-Every EoE handler owns an EoE state machine, that is used to send
-frames to the coupled slave and receive frames from the it via the EoE
-communication primitives. This state machine is showed in
-figure~\ref{fig:fsm-eoe}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.7\textwidth]{images/fsm-eoe}
-  \caption{Transition diagram of the EoE state machine}
-  \label{fig:fsm-eoe}
-\end{figure}
-
-\begin{description}
-\item[RX\_START] The beginning state of the EoE state machine. A
-  mailbox check datagram is sent, to query the slave's mailbox for new
-  frames. $\rightarrow$~\textit{RX\_CHECK}
-
-\item[RX\_CHECK] The mailbox check datagram is received. If the
-  slave's mailbox did not contain data, a transmit cycle is started.
-  $\rightarrow$~\textit{TX\_START}
-
-  If there are new data in the mailbox, a datagram is sent to fetch
-  the new data. $\rightarrow$~\textit{RX\_FETCH}
-
-\item[RX\_FETCH] The fetch datagram is received. If the mailbox data
-  do not contain a ``EoE Fragment request'' command, the data are
-  dropped and a transmit sequence is started.
-  $\rightarrow$~\textit{TX\_START}
-
-  If the received Ethernet frame fragment is the first fragment, a new
-  socket buffer is allocated. In either case, the data are copied into
-  the correct position of the socket buffer.
-
-  If the fragment is the last fragment, the socket buffer is forwarded
-  to the network stack and a transmit sequence is started.
-  $\rightarrow$~\textit{TX\_START}
-
-  Otherwise, a new receive sequence is started to fetch the next
-  fragment. $\rightarrow$~\textit{RX\_\-START}
-
-\item[TX\_START] The beginning state of a transmit sequence. It is
-  checked, if the transmittion queue contains a frame to send. If not,
-  a receive sequence is started. $\rightarrow$~\textit{RX\_START}
-
-  If there is a frame to send, it is dequeued. If the queue was
-  inactive before (because it was full), the queue is woken up with a
-  call to \textit{netif\_wake\_queue()}. The first fragment of the
-  frame is sent. $\rightarrow$~\textit{TX\_SENT}
-
-\item[TX\_SENT] It is checked, if the first fragment was sent
-  successfully. If the current frame consists of further fragments,
-  the next one is sent. $\rightarrow$~\textit{TX\_SENT}
-
-  If the last fragment was sent, a new receive sequence is started.
-  $\rightarrow$~\textit{RX\_START}
-\end{description}
-
-\paragraph{EoE Processing}
-
-To execute the EoE state machine of every active EoE handler, there
-must be a cyclic process. The easiest thing would be to execute the
-EoE state machines synchronously to the operation state machine (see
-section~\ref{sec:fsm-op}) with every realtime cycle. This approach has
-the following disadvantages:
-
-\begin{itemize}
-\item Only one EoE fragment can be sent or received every few cycles.
-  This causes the data rate to be very low, because the EoE state
-  machines are not executed in the time between the realtime
-  cycles. Moreover, the data rate would be dependent on the frequency
-  of the realtime process.
-\item The receiving and forwarding of frames to the kernel requires
-  the dynamic allocation of frames. Some realtime extensions do not
-  support calling memory allocation functions in realtime context, so
-  the EoE state machine may not be executed with each realtime cycle.
-\end{itemize}
-
-To overcome these problems, an own cyclic process is needed to
-asynchronously execute the EoE state machines. For that, the master
-owns a kernel timer, that is executed each timer interrupt. This
-guarantees a constant bandwidth, but poses the new problem of
-concurrent access to the master. The locking mechanisms needed for
-this are introduced in section~\ref{sec:concurr}.
-Section~\ref{sec:concurrency} gives practical implementation examples.
-
-\paragraph{Idle Mode}
-
-EoE data must also be exchanged idle mode, to guarantee the continuous
-availability of the connection to the EoE-capable slaves. Although
-there is no realtime module connected in this case, the master is
-still accessed by the idle state machine (see
-section~\ref{sec:fsm-idle}), that is executed by the master's
-workqueue. With the EoE timer running in addition, there is still
-concurrency, that has to be protected by a lock. Therefore the master
-owns an internal spinlock that is used protect master access during
-idle mode.
-
-\paragraph{Automatic Configuration}
-
-By default, slaves are left in \textit{INIT} state during idle mode.
-If an EoE interface is set to running state (i.~e. with the
-\textit{ifconfig up} command), the requested slave state of the
-related slave is automatically set to \textit{OP}, whereupon the idle
-state machine will attempt to configure the slave and put it into
-operation.
-
-%------------------------------------------------------------------------------
-
-\subsection{CANopen-over-EtherCAT (CoE)}
-\label{sec:coeimp}
-\index{CoE}
-
-The CANopen-over-EtherCAT protocol \cite[section~5.6]{alspec} is used
-to configure slaves on application level. Each CoE-capable slave
-provides a list of SDOs for this reason.
-
-\paragraph{SDO Configuration}
-
-The SDO configurations have to be provided by the realtime module.
-This is done via the \textit{ecrt\_slave\_conf\_sdo*()} methods (see
-section~\ref{sec:ecrt-slave}), that are part of the realtime
-interface. The slave stores the SDO configurations in a linked list,
-but does not apply them at once.
-
-\paragraph{SDO Download State Machine}
-
-The best time to apply SDO configurations is during the slave's
-\textit{PREOP} state, because mailbox communication is already
-possible and slave's application will start with updating input data
-in the succeeding \textit{SAVEOP} state. Therefore the SDO
-configuration has to be part of the slave configuration state machine
-(see section~\ref{sec:fsm-conf}): It is implemented via an SDO
-download state machine, that is executed just before entering the
-slave's \textit{SAVEOP} state. In this way, it is guaranteed that the
-SDO configurations are applied each time, the slave is reconfigured.
-
-The transition diagram of the SDO Download state machine can be seen
-in figure~\ref{fig:fsm-coedown}.
-
-\begin{figure}[htbp]
-  \centering
-  \includegraphics[width=.9\textwidth]{images/fsm-coedown}
-  \caption{Transition diagram of the CoE download state machine}
-  \label{fig:fsm-coedown}
-\end{figure}
-
-\begin{description}
-\item[START] The beginning state of the CoE download state
-  machine. The ``SDO Download Normal Request'' mailbox command is
-  sent. $\rightarrow$~\textit{REQUEST}
-
-\item[REQUEST] It is checked, if the CoE download request has been
-  received by the slave. After that, a mailbox check command is issued
-  and a timer is started. $\rightarrow$~\textit{CHECK}
-
-\item[CHECK] If no mailbox data is available, the timer is checked.
-  \begin{itemize}
-  \item If it timed out, the SDO download is aborted.
-    $\rightarrow$~\textit{ERROR}
-  \item Otherwise, the mailbox is queried again.
-    $\rightarrow$~\textit{CHECK}
-  \end{itemize}
-
-  If the mailbox contains new data, the response is fetched.
-  $\rightarrow$~\textit{RESPONSE}
-
-\item[RESPONSE] If the mailbox response could not be fetched, the data
-  is invalid, the wrong protocol was received, or a ``Abort SDO
-  Transfer Request'' was received, the SDO download is aborted.
-  $\rightarrow$~\textit{ERROR}
-
-  If a ``SDO Download Normal Response'' acknowledgement was received,
-  the SDO download was successful. $\rightarrow$~\textit{END}
-
-\item[END] The SDO download was successful.
-
-\item[ERROR] The SDO download was aborted due to an error.
-
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{User Space}
-\label{sec:user}
-\index{User space}
-
-For the master runs as a kernel module, accessing it is natively
-limited to analyzing syslog messages and controlling using modutils.
-
-It is necessary to implement further interfaces, that make it easier
-to access the master from user space and allow a finer influence. It
-should be possible to view and to change special parameters at runtime.
-
-Bus visualization is a second point: For development and debugging
-purposes it would be nice, if one could show the connected slaves with
-a single command.
-
-Another aspect is automatic startup and configuration. If the master
-is to be integrated into a running system, it must be able to
-automatically start with a persistent configuration.
-
-A last thing is monitoring EtherCAT communication. For debugging
-purposes, there had to be a way to analyze EtherCAT datagrams. The
-best way would be with a popular network analyzer, like Wireshark
-\cite{wireshark} (the former Ethereal) or others.
-
-This section covers all those points and introduces the interfaces and
-tools to make all that possible.
-
-%------------------------------------------------------------------------------
-
-\subsection{The Sysfs Interface}
-\label{sec:sysfs}
-
-The system filesystem (Sysfs\index{Sysfs}) was introduced with Linux
-kernel 2.5 and is a well-defined interface for drivers to export
-information to user space. It serves also as an relief for the process
-filesystem (Procfs), where over the years much non-process information
-was concentrated.
-
-Sysfs exports information about devices, classes and busses via a
-virtual filesystem, usually mounted to \textit{/sys}. The EtherCAT
-master slightly differs from this concept, because the only physical
-device is the network adapter it uses for bus communication, which is
-already represented in Sysfs. For the EtherCAT bus is no system bus
-like PCI (with device and driver structures), it would not make any
-sense to represent it as bus structure in Sysfs.
-
-Therefore, the EtherCAT master is represented as a new directory
-directly unter the Sysfs root. Every master gets its own Sysfs entry
-named \textit{ethercatX}, where X is the index of the master. Two
-masters would result in the directories \textit{/sys/ethercat0} and
-\textit{/sys/ethercat1}, respectively.
-
-The Sysfs base class in the kernel code is the \textit{kobject}
-structure. Each object structure, that is to be represented in Sysfs,
-has to contain such a structure, because due to the concurrent access
-(through ``normal'' kernel code and Sysfs code) the object deletion
-gets a little more complicated: The object may not be freed until no
-instance uses it any more. Therefore, each kobject maintains a
-reference counter. If the reference counter gets zero, the object is
-finally freed. A kobject can be registered to appear as a directory in
-Sysfs with a call to \textit{kobject\_add()}. Each kobject type can
-define attributes, that appear as files in the kobject's
-directory. Callback functions have to be provided for reading (and
-perhaps writing) access.
-
-\subsubsection{Master Attributes}
-\label{sec:sysfs-master}
-
-Below is a typical listing of the masters Sysfs directory (that is a
-file system representation of the master's kobject):
-
-\begin{lstlisting}
-  host> `\textbf{ls /sys/ethercat0}`
-  debug_level          slave000  slave003  slave006
-  eeprom_write_enable  slave001  slave004  slave007
-  info                 slave002  slave005  slave008
-\end{lstlisting}
-
-The following attributes exist in the master directory:
-
-\begin{description}
-\item[debug\_level] (read/write) This attribute contains the master's
-  debug level, which controls, how much information is printed into
-  syslog. The values 0 (no additional debug messages), 1 (a few
-  additional debug messages) and 2 (all additional debug messages) are
-  defined. Writing is done with command like
-
-  \begin{lstlisting}[gobble=4]
-    host# `\textbf{echo 1 > /sys/ethercat0/debug\_level}`
-  \end{lstlisting}
-
-  and is receipted with a syslog message by the master:
-
-  \begin{lstlisting}[gobble=4]
-    EtherCAT: Master debug level set to 1.
-  \end{lstlisting}
-
-\item[enable\_eeprom\_writing] (read/write) See
-  section~\ref{sec:eepromaccess} for how to use this attribute.
-
-\item[info] (read only) This attribute contains information about the
-  master. Example contents are below:
-
-  \begin{lstlisting}[gobble=4]
-    host> `\textbf{cat /sys/ethercat0/info}`
-
-    Mode: IDLE
-    Slaves: 9
-
-    Timing (min/avg/max) [us]:
-      Idle cycle: 4 / 4.38 / 34
-      EoE cycle: 9 / 11.91 / 23
-
-    EoE statistics (RX/TX) [bps]:
-      eoe0: 0 / 3184
-  \end{lstlisting}
-
-  The mode can be \textit{ORPHANED}, \textit{IDLE} or
-  \textit{OPERATION}. The other parameters are self-explanatory.
-
-\end{description}
-
-\subsubsection{Domain Attributes}
-\label{sec:sysfs-domain}
-
-In operation mode, each created domain is represented as a directory
-\textit{domainX}, where X is the domain index. Below is a listing of
-the domain directory contents:
-
-\begin{lstlisting}
-  host> `\textbf{ls /sys/ethercat0/domain0}`
-  image_size
-\end{lstlisting}
-
-The domain directories currently only export the domain's image size.
-It is planned to export the whole process data mapping for debugging
-purposes.
-
-\subsubsection{Slave Attributes}
-\label{sec:sysfs-slave}
-
-Each slave on the bus is represented in its own directory
-\textit{slaveXXX}, where XXX is the slave's 3-digit ring position in
-the EtherCAT bus. Below is a listing of a slave directory:
-
-\begin{lstlisting}
-  host> `\textbf{ls /sys/ethercat0/slave003}`
-  eeprom  info  state
-\end{lstlisting}
-
-\begin{description}
-\item[eeprom] (read/write) See section~\ref{sec:eepromaccess} for how
-  to use this attribute.
-
-\item[info] (read only) This attribute contains a bunch of information
-  about the slave. Below is an example output:
-
-  \begin{lstlisting}[gobble=4]
-    host> `\textbf{cat /sys/ethercat0/slave003/info}`
-
-    Name: EL4132 2K. Ana. Ausgang +/-10V
-    Vendor ID: 0x00000002
-    Product code: 0x10243052
-
-    State: INIT
-    Ring position: 3
-    Advanced position: 1:3
-
-    Data link status:
-      Port 0 (EBUS) Link down, Loop open, Signal detected
-      Port 1 (EBUS) Link down, Loop open, Signal detected
-      Port 2 (EBUS) Link down, Loop closed, No signal
-      Port 3 (EBUS) Link down, Loop closed, No signal
-
-    Mailboxes:
-      RX mailbox: 0x1800/246, TX mailbox: 0x18F6/246
-      Supported protocols: CoE, FoE
-
-    SII data:
-      Group: AnaOut
-      Image: TERM_AO
-      Order#: EL4132
-
-    Sync-Managers:
-      0: 0x1800, length 246, control 0x26, enable
-      1: 0x18F6, length 246, control 0x22, enable
-      2: 0x1000, length 0, control 0x24, enable
-      3: 0x1100, length 0, control 0x20, enable
-
-    PDOs:
-      RXPDO "Channel 1" (0x1600), Sync-Manager 2
-        "Output" 0x6411:1, 16 bit
-      RXPDO "Channel 2" (0x1601), Sync-Manager 2
-        "Output" 0x6411:2, 16 bit
-  \end{lstlisting}
-
-  This is nearly all of the SII category information needed to
-  configure the slave, supplemented with state and addressing
-  information.
-
-\item[state] (read/write) This attribute contains the slave's state.
-  It can be read or written:
-
-  \begin{lstlisting}[gobble=4]
-    host# `\textbf{cat /sys/ethercat0/slave003/state}`
-    OP
-    host# `\textbf{echo SAVEOP > /sys/ethercat0/slave003/state}`
-  \end{lstlisting}
-
-  This command should also be receipted with a syslog message:
-
-  \begin{lstlisting}[gobble=4]
-    EtherCAT: Accepted new state SAVEOP for slave 3.
-    EtherCAT: Changing state of slave 3 from OP to SAVEOP.
-    EtherCAT: Slave states: INIT, SAVEOP, OP.
-  \end{lstlisting}
-
-  After the new requested state was accepted from user space, the
-  operation state machine (see section~\ref{sec:fsm-op}) or the idle
-  state machine (section~\ref{sec:fsm-idle}) notices, that the
-  requested slave state differs from the current one, and therefore
-  executes the slave configuration state machine, until the slave has
-  reached the requested state.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsubsection{E$^2$PROM Access}
-\label{sec:eepromaccess}
-\index{E$^2$PROM!Access}
-
-It is possible to directly read or write the complete E$^2$PROM
-contents of the slaves. This was introduced for the reasons below:
-
-\begin{itemize}
-\item The format of the E$^2$PROM data is still in development and
-  categories can be added in the future. With read and write access,
-  the complete memory contents can be easily backed up and restored.
-\item Some E$^2$PROM data fields have to be altered (like the alias
-  address). A quick writing must be possible for that.
-\item Through read access, analyzing category data is possible from
-  user space.
-\end{itemize}
-
-Reading out E$^2$PROM data is as easy as reading other
-attributes. Though the data are in binary format, analyzation is
-easier with a tool like \textit{hexdump}:
-
-\begin{lstlisting}
-  host> `\textbf{cat /sys/ethercat0/slave003/eeprom | hexdump}`
-  0000000 0103 0000 0000 0000 0000 0000 0000 008c
-  0000010 0002 0000 3052 07f0 0000 0000 0000 0000
-  0000020 0000 0000 0000 0000 0000 0000 0000 0000
-  ...
-\end{lstlisting}
-
-Backing up E$^2$PROM contents gets as easy as copying a file:
-
-\begin{lstlisting}
-  host> `\textbf{cp /sys/ethercat0/slave003/eeprom slave003.eep}`
-\end{lstlisting}
-
-Writing access is only possible as \textit{root}. Moreover writing has
-to be explicitly enabled and is only allowed in idle mode. This is a
-safety measure, because without the correct memory contents, a slave
-is unusable. Writing E$^2$PROM contents in operation mode is not
-provided yet.
-
-E$^2$PROM writing is enabled with the command below:
-
-\begin{lstlisting}
-  host# `\textbf{echo 1 > /sys/ethercat0/eeprom\_write\_enable}`
-\end{lstlisting}
-
-The success can be seen in the syslog messages again:
-
-\begin{lstlisting}
-  EtherCAT: Slave EEPROM writing enabled.
-\end{lstlisting}
-
-Now, it is possible to write E$^2$PROM contents to a slave. The master
-will accept data through the \textit{eeprom} file and will perform a
-short validation of the contents, before starting the write operation.
-This validation checks the complete size and the category headers.
-
-\begin{lstlisting}
-  host# `\textbf{cat slave003.eep > /sys/ethercat0/slave003/eeprom}`
-\end{lstlisting}
-
-The write operation can take a few seconds.
-
-\begin{lstlisting}
-  EtherCAT: EEPROM writing scheduled for slave 3, 88 words.
-  EtherCAT: Writing EEPROM of slave 3...
-  EtherCAT: Finished writing EEPROM of slave 3.
-\end{lstlisting}
-
-%------------------------------------------------------------------------------
-
-\subsection{User Space Tools}
-\index{User space!Tools}
-
-There is a user space tool called \textit{lsec}\index{lsec} (``List
-EtherCAT'') to visualize the EtherCAT bus. Running it usually results
-in an output like this:
-
-\begin{lstlisting}
-  host> `\textbf{lsec}`
-  EtherCAT bus listing for master 0:
-     0  1:0  OP      EK1100 Ethernet Kopplerklemme (2A E-Bus)
-     1  1:1  INIT    EL4132 2K. Ana. Ausgang +/-10V
-     2  1:2  INIT    EL4132 2K. Ana. Ausgang +/-10V
-     3  1:3  SAVEOP  EL4132 2K. Ana. Ausgang +/-10V
-     4  1:4  INIT    EL5101 Incremental Encoder Interface
-     5  1:5  INIT    EL1014 4K. Dig. Eingang 24V, 10s
-     6  1:6  OP      EL6601 1 Port Switch (Ethernet, CoE)
-     7  1:7  INIT    EL5101 Incremental Encoder Interface
-     8  1:8  INIT    EL5001 1K. SSI Encoder
-\end{lstlisting}
-
-Every slave is displayed as one text row. The first column shows its
-ring position, the second displays the ``advanced position address''
-(see section~\ref{sec:addr}) and the third column displays the current
-slave state. The last column is the slave's name, as it appears in the
-``general'' E$^2$PROM category.
-
-The lsec program is a Perl script, that evaluates the Sysfs
-\textit{info} attributes of the slaves (see
-section~\ref{sec:sysfs-slave}). This is done for master $0$ by
-default, but the master index can be specified via command line:
-
-\begin{lstlisting}
-  host> `\textbf{lsec -h}`
-  Usage: ec_list [OPTIONS]
-          -m <IDX>    Query master <IDX>.
-          -h          Show this help.
-\end{lstlisting}
-
-This script has proved as useful for troubleshooting: If it displays
-slaves, the master is up and running, and the bus connection is
-present, too. It is also useful when building up a bus: It can verify
-the list of slaves and help to create a process data image (see
-chapter~\ref{chapter:usage}).
-
-%------------------------------------------------------------------------------
-
-\subsection{System Integration}
-\label{sec:system}
-
-To integrate the EtherCAT master into a running system, it has to be
-guaranteed, that it is started on system startup. In addition, there has
-to be a persistent configuration, that is also applied on startup.
-
-\subsubsection{The EtherCAT Init Script}
-\label{sec:init}
-\index{Init script}
-
-The EtherCAT master provides an ``init script'', that conforms to the
-requirements of the ``Linux Standard Base'' (LSB\index{LSB},
-\cite{lsb}). The script is installed to \textit{/etc/init.d/ethercat},
-so that the master can be easily inserted as a service. The different
-Linux distributions offer different ways to mark the service for
-starting and stopping in certain runlevels (for example, SUSE provides
-the \textit{insserv} command).
-
-To provide service dependencies (i.~e. which services have to be
-started before) right inside the init script code, LSB defines a
-special comment block. System tools can extract this information to
-insert the EtherCAT init script at the correct place in the startup
-sequence:
-
-\begin{lstlisting}
-  ### BEGIN INIT INFO
-  # Provides:          ethercat
-  # Required-Start:    $local_fs $syslog $network
-  # Should-Start:      $time
-  # Required-Stop:     $local_fs $syslog $network
-  # Should-Stop:       $time
-  # Default-Start:     3 5
-  # Default-Stop:      0 1 2 6
-  # Short-Description: EtherCAT master modules
-  # Description:
-  ### END INIT INFO
-\end{lstlisting}
-
-The init script can also be used for manually starting and stopping
-the EtherCAT master. It has to be executed with one of the parameters
-\textit{start}, \textit{stop}, \textit{restart} or \textit{status}.
-Besides, a link to the script is placed at
-\textit{/usr/sbin/rcethercat} for easier access.
-
-\begin{lstlisting}
-  host# `\textbf{/etc/init.d/ethercat restart}`
-  Shutting down EtherCAT master                done
-  Starting EtherCAT master                     done
-\end{lstlisting}
-
-\subsubsection{The EtherCAT Sysconfig File}
-\label{sec:sysconfig}
-\index{Sysconfig file}
-
-For persistent configuration, the init script uses a sysconfig file
-installed to \textit{/etc/sys\-config/ethercat}, that is mandatory for
-the init script. The sysconfig file contains all configuration
-variables needed to operate a master:
-
-\begin{description}
-\item[DEVICE\_INDEX] This variable must contain the PCI index of the
-  EtherCAT device.  Setting this is mandatory for the EtherCAT init
-  script. Default: $-1$
-\item[EOE\_INTERFACES] The number of virtual Ethernet-over-EtherCAT
-  interfaces, every master creates on startup. See
-  section~\ref{sec:eoeimp}. Default: $0$
-\item[EOE\_BRIDGE] If this variable is set, all EoE interfaces will be
-  added to a network bridge according to IEEE 802.1D after master
-  startup. The variable must contain the name of the bridge. To use
-  this functionality, the kernel must be configured with the
-  \textit{CONFIG\_BRIDGE} option and the \textit{bridge-utils} package
-  must be installed (i.~e. the \textit{brctl} command is needed).
-\item[EOE\_IP\_ADDRESS] The IP address of the EoE bridge. Setting this
-  together with \textit{EOE\_IP\_NETMASK} will let the local host
-  communicate with devices on the EoE bridge.
-\item[EOE\_IP\_NETMASK] IP netmask of the EoE bridge.
-\item[EOE\_EXTRA\_INTERFACES] The list of extra interfaces to include
-  in the EoE brid\-ge. Set this to interconnect the EoE bridge with
-  other local interfaces. If \textit{EOE\_\-BRIDGE} is empty or
-  undefined, setting this variable has no effect. Important: The IP
-  address of the listed interfaces will be cleared. Setting
-  \textit{EOE\_\-IP\_\-ADDRESS} and \textit{EOE\_IP\_NETMASK} will
-  re-enable them for IP traffic.
-\item[EOE\_GATEWAY] The IP address of the default gateway. If this
-  variable is set, the gateway will be renewed after bridge
-  installation. This is necessary, if the default gateway's interface
-  is one of the \textit{EOE\_EXTRA\_INTERFACES}.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\subsection{Monitoring and Debugging}
-\label{sec:debug}
-\index{Monitoring}
-
-For debugging purposes, every EtherCAT master registeres a read-only
-network interface \textit{ecX}, where X is a number, provided by the
-kernel on device registration. While it is ``up'', the master forwards
-every frame sent and received to this interface.
-
-This makes it possible to connect an network monitor (like Wireshark
-or tcpdump) to the debug interface and monitor the EtherCAT frames.
-
-It has to be considered, that can be frame rate can be very high. The
-idle state machine usually runs every kernel timer interrupt (up to
-$1$~kHz) and with a connected realtime module, the rate can be even
-higher.
-
-\paragraph{Attention:} The socket buffers needed for the operation of
-the debugging interface have to be allocated dynamically. Some Linux
-realtime extensions do not allow this in realtime context!
-
-%------------------------------------------------------------------------------
-
-\section{Timing Aspects}
-\label{sec:timing}
-
-Although EtherCAT's timing is highly deterministic and therefore
-timing issues are rare, there are a few aspects that can (and should
-be) dealt with.
-
-%------------------------------------------------------------------------------
-
-\subsection{Realtime Interface Profiling}
-\label{sec:timing-profile}
-\index{Realtime!Profiling}
-
-One of the most important timing aspects are the runtimes of the
-realtime interface functions, that are called in cyclic context. These
-functions make up an important part of the overall timing of the
-realtime module. To measure the timing of the functions, the following
-code was used:
-
-\begin{lstlisting}[gobble=2,language=C]
-  c0 = get_cycles();
-  ecrt_master_receive(master);
-  c1 = get_cycles();
-  ecrt_domain_process(domain1);
-  c2 = get_cycles();
-  ecrt_master_run(master);
-  c3 = get_cycles();
-  ecrt_master_send(master);
-  c4 = get_cycles();
-\end{lstlisting}
-
-Between each call of an interface function, the CPU timestamp counter
-is read. The counter differences are converted to microseconds with
-help of the \textit{cpu\_khz} variable, that contains the number of
-increments per millisecond.
-
-For the actual measuring, a system with a $2.0$~GHz CPU was used, that
-ran the above code in an RTAI thread with a cycle time of $100$
-\textmu s.  The measuring was repeated $n = 100$ times and the results
-were averaged. These can be seen in table~\ref{tab:profile}.
-
-\begin{table}[htpb]
-  \centering
-  \caption{Profiling of a Realtime Cycle on a $2.0$~GHz Processor}
-  \label{tab:profile}
-  \vspace{2mm}
-  \begin{tabular}{l|r|r}
-    Element & Mean Duration [\textmu s] & Standard Deviancy [\textmu s] \\
-    \hline
-    \textit{ecrt\_master\_receive()} & 8.04 & 0.48\\
-    \textit{ecrt\_domain\_process()} & 0.14 & 0.03\\
-    \textit{ecrt\_master\_run()} & 0.29 & 0.12\\
-    \textit{ecrt\_master\_send()} & 2.18 & 0.17\\ \hline
-    Complete Cycle & 10.65 & 0.69\\ \hline
-  \end{tabular}
-\end{table}
-
-It is obvious, that the the functions accessing hardware make up the
-lion's share. The \textit{ec\_master\_receive()} executes the ISR of
-the Ethernet device, analyzes datagrams and copies their contents into
-the memory of the datagram objects. The \textit{ec\_master\_send()}
-assembles a frame out of different datagrams and copies it to the
-hardware buffers. Interestingly, this makes up only a quarter of the
-receiving time.
-
-The functions that only operate on the masters internal data
-structures are very fast ($\Delta t < 1$~\textmu s). Interestingly the
-runtime of \textit{ec\_domain\_process()} has a small standard
-deviancy relative to the mean value, while this ratio is about twice
-as big for \textit{ec\_master\_run()}: This probably results from the
-latter function having to execute code depending on the current state
-and the different state functions are more or less complex.
-
-For a realtime cycle makes up about $10$~\textmu s, the theoretical
-frequency can be up to $100$~kHz. For two reasons, this frequency
-keeps being theoretical:
-
-\begin{enumerate}
-\item The processor must still be able to run the operating system
-  between the realtime cycles.
-\item The EtherCAT frame must be sent and received, before the next
-  realtime cycle begins. The determination of the bus cycle time is
-  difficult and covered in section~\ref{sec:timing-bus}.
-\end{enumerate}
-
-%------------------------------------------------------------------------------
-
-\subsection{Bus Cycle Measuring}
-\label{sec:timing-bus}
-\index{Bus cycle}
-
-For measuring the time, a frame is ``on the wire'', two timestamps
-must be be taken:
-
-\begin{enumerate}
-\item The time, the Ethernet hardware begins with physically sending
-  the frame.
-\item The time, the frame is completely received by the Ethernet
-  hardware.
-\end{enumerate}
-
-Both times are difficult to determine. The first reason is, that the
-interrupts are disabled and the master is not notified, when a frame
-is sent or received (polling would distort the results). The second
-reason is, that even with interrupts enabled, the time from the event
-to the notification is unknown. Therefore the only way to confidently
-determine the bus cycle time is an electrical measuring.
-
-Anyway, the bus cycle time is an important factor when designing
-realtime code, because it limits the maximum frequency for the cyclic
-part of the realtime module. In practice, these timing parameters are
-highly dependent on the hardware and often a trial and error method
-must be used to determine the limits of the system.
-
-The central question is: What happens, if the cycle frequency is too
-high? The answer is, that the EtherCAT frames that have been sent at
-the end of the cycle are not yet received, when the next cycle starts.
-First this is noticed by \textit{ecrt\_domain\_process()}, because the
-working counter of the process data datagrams were not increased. The
-function will notify the user via syslog\footnote{To limit syslog
-  output, a mechanism has been implementet, that outputs a summarized
-  notification at maximum once a second.}. In this case, the process
-data keeps being the same as in the last cycle, because it is not
-erased by the domain. When the domain datagrams are queued again, the
-master notices, that they are already queued (and marked as sent). The
-master will mark them as unsent again and output a warning, that
-datagrams were ``skipped''.
-
-On the mentioned $2.0$~GHz system, the possible cycle frequency can be
-up to $25$~kHz without skipped frames. This value can surely be
-increased by choosing faster hardware. Especially the RealTek network
-hardware could be replaced by a faster one. Besides, implementing a
-dedicated ISR for EtherCAT devices would also contribute to increasing
-the latency. These are two points on the author's to-do list.
-
-%------------------------------------------------------------------------------
-
-\chapter{Using the EtherCAT Master}
-\label{chapter:usage}
-\index{Master!Usage}
-
-This chapter will give practical examples of how to use the EtherCAT
-master via the realtime interface by writing a realtime module.
-
-Section~\ref{sec:make} shows how to compile and install the master,
-while the sections~\ref{sec:mini} to~\ref{sec:concurrency} give
-examples for different realtime modules.
-
-%------------------------------------------------------------------------------
-
-\section{Compiling and Installing}
-\label{sec:make}
-\index{Master!Compilation}
-
-The current EtherCAT master code is available at~\cite{etherlab}.
-After downloading the \textit{tar.bz2} file, it has to be unpacked
-with the command below (or similar):
-
-\begin{lstlisting}
-  host> `\textbf{tar xjf ethercat-stable-1.1-r513-src.tar.bz2}`
-  host> `\textbf{cd ethercat-stable-1.1-r513-src}`
-\end{lstlisting}
-
-For compilation, the kernel sources are needed. Basically any kernel
-sources are appropriate\footnote{If a realtime extension is to be
-  used, the kernel has to be patched before that.}, that are
-configured with networking. If the host kernel is not the running
-kernel, a copy of the configuration template has to be made:
-
-\begin{lstlisting}
-  host> `\textbf{cp ethercat.conf.tmpl ethercat.conf}`
-\end{lstlisting}
-
-Now the \textit{\$KERNEL} variable inside the \textit{ethercat.conf}
-file can be adjusted to reflect the appropriate kernel version. If
-everything is correct now, the sucessive call to
-
-\begin{lstlisting}
-  host> `\textbf{make}`
-\end{lstlisting}
-
-will result in no errors.
-
-The following commands have to be entered as \textit{root}: To install
-the kernel modules, the init script, the sysconfig file and the user
-space tools, the below command has to be executed:
-
-\begin{lstlisting}
-  host# `\textbf{make install}`
-\end{lstlisting}
-
-If the sysconfig file did not exist yet, the user is notified to edit
-it, before running the master. For the contents of the file, see
-section~\ref{sec:sysconfig}. To give a short summary: The most
-important thing is to adjust the \textit{\$DEVICE\_INDEX} variable. It
-has to be set to the index of the compatible network device to use
-with EtherCAT, where the order of devices is dependent on their
-position in the PCI bus. If this is not known, the index can be
-determinded with trial and error, but it has to be considered that a
-wrong value can cause a loss of network connection.
-
-After the basic configuration is done, the master can be started with
-the below command:
-
-\begin{lstlisting}
-  host# `\textbf{/etc/init.d/ethercat start}`
-\end{lstlisting}
-
-The operation of the master can be observed by looking at the
-syslog\index{syslog} messages, which should look like the ones below:
-
-\begin{lstlisting}[numbers=left]
-  EtherCAT: Master driver, 1.1 (stable) - rev. 513,
-      compiled by fp at Aug 09 2006 10:23:20
-  EtherCAT: Initializing 1 EtherCAT master(s)...
-  EtherCAT: Initializing master 0.
-  EtherCAT: Master driver initialized.
-  ec_8139too Fast Ethernet driver 0.9.27 Revision 513,
-      compiled by fp at Aug 09 2006 10:23:20
-  ec_device_index is 0
-  ACPI: PCI Interrupt 0000:01:00.0[A] -> Link [LNKC]
-      -> GSI 11 (level, low) -> IRQ 11
-  ec0: RealTek RTL8139 at 0xd047c000, 00:c0:26:00:c6:aa, IRQ 11
-  ec0:  Identified 8139 chip type 'RTL-8100B/8139D'
-  Registering EtherCAT device...
-  Starting EtherCAT device...
-  EtherCAT: Link state changed to UP.
-  EtherCAT: Starting Idle mode.
-  EtherCAT: 11 slaves responding.
-  EtherCAT: Slave states: INIT, OP.
-  EtherCAT: Scanning bus.
-  EtherCAT: Bus scanning completed.
-  EtherCAT: No EoE handlers coupled.
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1}] The master module is loaded,
-  and one master is initialized.
-\item[\normalfont\textcircled{\tiny 6}] The EtherCAT-capable RTL8139
-  device driver is loaded. It connects its first network device to the
-  master.
-\item[\normalfont\textcircled{\tiny 16}] The master starts idle mode
-  and begins scanning the bus for slaves.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{A Minimal Example Module}
-\label{sec:mini}
-\index{Examples!Minimal}
-
-This section will explain the usage of the EtherCAT master from a
-minimal kernel module. The complete module code is obtainable as a
-part of the EtherCAT master code release (see~\cite{etherlab}, file
-\textit{examples/mini/mini.c}).
-
-The minimal example uses a kernel timer (software interrupt) to handle
-cyclic code. After the timer function is executed, it re-adds itself
-with a delay of one \textit{jiffy}\index{jiffies}, which results in a
-timer frequency of \textit{HZ}\nomenclature{HZ}{Kernel macro
-  containing the timer interrupt frequency}
-
-The module-global variables, needed to operate the master can be seen
-in listing~\ref{lst:minivar}.
-
-\begin{lstlisting}[language=C,numbers=left,caption={Minimal
-    variables},label=lst:minivar]
-  struct timer_list timer;
-
-  ec_master_t *master = NULL;
-  ec_domain_t *domain1 = NULL;
-
-  void *r_dig_in, *r_ana_out;
-
-  ec_pdo_reg_t domain1_pdos[] = {
-          {"1", Beckhoff_EL1014_Inputs, &r_dig_in},
-          {"2", Beckhoff_EL4132_Ouput1, &r_ana_out},
-          {}
-  };
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1}] There is a timer object
-  declared, that is needed to tell the kernel to install a timer and
-  execute a certain function, if it runs out. This is done by a
-  variable of the \textit{timer\_list} structure.
-\item[\normalfont\textcircled{\tiny 3} -- \textcircled{\tiny 4}] There
-  is a pointer declared, that will later point to a requested EtherCAT
-  master.  Additionally there is a pointer to a domain object needed,
-  that will manage process data IO.
-\item[\normalfont\textcircled{\tiny 6}] The pointers \textit{r\_*}
-  will later point to the \underline{r}aw process data values inside
-  the domain memory. The addresses they point to will be set during a
-  call to \textit{ec\_\-master\_\-activate()}, that will create the
-  domain memory and configure the mapped process data image.
-\item[\normalfont\textcircled{\tiny 8} -- \textcircled{\tiny 12}] The
-  configuration of the mapping of certain PDOs in a domain can easily
-  be done with the help of an initialization array of the
-  \textit{ec\_pdo\_reg\_t} type, defined as part of the realtime
-  interface. Each record must contain the ASCII bus-address of the
-  slave (see section~\ref{sec:addr}), the slave's vendor ID and
-  product code, and the index and subindex of the PDO to map (these
-  four fields can be specified in junction, by using one of the
-  defines out of the \textit{include/ecdb.h} header). The last field
-  has to be the address of the process data pointer, so it can later
-  be redirected appropriately. Attention: The initialization array
-  must end with an empty record (\textit{\{\}})!
-\end{description}
-
-The initialization of the minimal realtime module is done by the
-``Minimal init function'' in listing~\ref{lst:miniinit}.
-
-\begin{lstlisting}[language=C,numbers=left,caption={Minimal init
-    function},label={lst:miniinit}]
-  int __init init_mini_module(void)
-  {
-          if (!(master = ecrt_request_master(0))) {
-                  goto out_return;
-          }
-
-          if (!(domain1 = ecrt_master_create_domain(master))) {
-                  goto out_release_master;
-          }
-
-          if (ecrt_domain_register_pdo_list(domain1,
-                                            domain1_pdos)) {
-                  goto out_release_master;
-          }
-
-          if (ecrt_master_activate(master)) {
-                  goto out_release_master;
-          }
-
-          ecrt_master_prepare(master);
-
-          init_timer(&timer);
-          timer.function = run;
-          timer.expires = jiffies + 10;
-          add_timer(&timer);
-
-          return 0;
-
-        out_release_master:
-          ecrt_release_master(master);
-        out_return:
-          return -1;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] It is tried to request the
-  first EtherCAT master (index 0). On success, the
-  \textit{ecrt\_\-request\_\-master()} function returns a pointer to
-  the reserved master, that can be used as an object to following
-  functions calls. On failure, the function returns \textit{NULL}.
-\item[\normalfont\textcircled{\tiny 7}] In order to exchange process
-  data, a domain object has to be created. The
-  \textit{ecrt\_\-master\_\-create\_domain()} function also returns a
-  pointer to the created domain, or \textit{NULL} in error case.
-\item[\normalfont\textcircled{\tiny 11}] The registration of domain
-  PDOs with an initialization array results in a single function call.
-  Alternatively the data fields could be registered with individual
-  calls of \textit{ecrt\_domain\_register\_pdo()}.
-\item[\normalfont\textcircled{\tiny 16}] After the configuration of
-  process data mapping, the master can be activated for cyclic
-  operation. This will configure all slaves and bring them into
-  \textit{OP} state.
-\item[\normalfont\textcircled{\tiny 20}] This call is needed to avoid
-  a case differentiation in cyclic operation: The first operation in
-  cyclic mode is a receive call. Due to the fact, that there is
-  nothing to receive during the first cycle, there had to be an
-  \textit{if}-statement to avoid a warning. A call to
-  \textit{ec\_master\_prepare()} sends a first datagram containing a
-  process data exchange datagram, so that the first receive call will
-  not fail.
-\item[\normalfont\textcircled{\tiny 22} -- \textcircled{\tiny 25}] The
-  master is now ready for cyclic operation. The kernel timer that
-  cyclically executes the \textit{run()} function is initialized and
-  started.
-\end{description}
-
-The coding of a cleanup function fo the minimal module can be seen in
-listing~\ref{lst:miniclean}.
-
-\begin{lstlisting}[language=C,numbers=left,caption={Minimal cleanup
-    function},label={lst:miniclean}]
-  void __exit cleanup_mini_module(void)
-  {
-          del_timer_sync(&timer);
-          ecrt_master_deactivate(master);
-          ecrt_release_master(master);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] To cleanup the module, it it
-  necessary to stop the cyclic processing. This is done by a call to
-  \textit{del\_timer\_sync()} which safely removes a queued timer
-  object. It is assured, that no cyclic work will be done after this
-  call returns.
-\item[\normalfont\textcircled{\tiny 4}] This call deactivates the
-  master, which results in all slaves being brought to their
-  \textit{INIT} state again.
-\item[\normalfont\textcircled{\tiny 5}] This call releases the master,
-  removes any existing configuration and silently starts the idle
-  mode. The value of the master pointer is invalid after this call and
-  the module can be safely unloaded.
-\end{description}
-
-The final part of the minimal module is that for the cyclic work. Its
-coding can be seen in listing~\ref{lst:minirun}.
-
-\begin{lstlisting}[language=C,numbers=left,caption={Minimal cyclic
-    function},label={lst:minirun}]
-  void run(unsigned long data)
-  {
-          static uint8_t dig_in_0;
-
-          ecrt_master_receive(master);
-          ecrt_domain_process(domain1);
-
-          dig_in_0 = EC_READ_BIT(r_dig_in, 0);
-          EC_WRITE_S16(r_ana_out, dig_in_0 * 0x3FFF);
-
-          ecrt_master_run(master);
-          ecrt_master_send(master);
-
-          timer.expires += 1; // frequency = HZ
-          add_timer(&timer);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 5}] The cyclic processing starts
-  with receiving datagrams, that were sent in the last cycle. The
-  frames containing these datagrams have to be received by the network
-  interface card prior to this call.
-\item[\normalfont\textcircled{\tiny 6}] The process data of domain 1
-  has been automatically copied into domain memory while datagram
-  reception. This call checks the working counter for changes and
-  re-queues the domain's datagram for sending.
-\item[\normalfont\textcircled{\tiny 8}] This is an example for reading
-  out a bit-oriented process data value (i.~e. bit 0) via the
-  \textit{EC\_READ\_BIT()} macro. See section~\ref{sec:macros} for
-  more information about those macros.
-\item[\normalfont\textcircled{\tiny 9}] This line shows how to write a
-  signed, 16-bit process data value. In this case, the slave is able
-  to output voltages of $-10$~V to $+10$~V with a resolution of 16
-  bit.  This write command outputs either $0$~V or $+5$~V, depending
-  of the value of \textit{dig\_in\_0}.
-\item[\normalfont\textcircled{\tiny 11}] This call runs the master's
-  operation state machine (see section~\ref{sec:fsm-op}). A single
-  state is processed, and datagrams are queued. Mainly bus observation
-  is done: The bus state is determined and in case of slaves that lost
-  their configuration, reconfiguration is tried.
-\item[\normalfont\textcircled{\tiny 12}] This method sends all queued
-  datagrams, in this case the domain's datagram and one of the master
-  state machine. In best case, all datagrams fit into one frame.
-\item[\normalfont\textcircled{\tiny 14} -- \textcircled{\tiny 15}]
-  Kernel timers are implemented as ``one-shot'' timers, so they have
-  to be re-added after each execution. The time of the next execution
-  is specified in \textit{jiffies} and will happen at the time of the
-  next system timer interrupt. This results in the \textit{run()}
-  function being executed with a frequency of \textit{HZ}.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{An RTAI Example Module}
-\label{sec:rtai}
-\index{Examples!RTAI}
-
-The whole code can be seen in the EtherCAT master code release
-(see~\cite{etherlab}, file \textit{examples/rtai/rtai\_sample.c}).
-
-Listing~\ref{lst:rtaivar} shows the defines and global variables
-needed for a minimal RTAI module with EtherCAT processing.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI task
-    declaration},label={lst:rtaivar}]
-  #define FREQUENCY 10000
-  #define TIMERTICKS (1000000000 / FREQUENCY)
-
-  RT_TASK task;
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1} -- \textcircled{\tiny 2}] RTAI
-  takes the cycle period as nanoseconds, so the easiest way is to
-  define a frequency and convert it to a cycle time in nanoseconds.
-\item[\normalfont\textcircled{\tiny 4}] The \textit{task} variable
-  later contains information about the running RTAI task.
-\end{description}
-
-Listing~\ref{lst:rtaiinit} shows the module init function for the RTAI
-module. Most lines are the same as in listing~\ref{lst:miniinit},
-differences come up when starting the cyclic code.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI module init
-    function},label={lst:rtaiinit}]
-  int __init init_mod(void)
-  {
-          RTIME requested_ticks, tick_period, now;
-
-          if (!(master = ecrt_request_master(0))) {
-                  goto out_return;
-          }
-
-          if (!(domain1 = ecrt_master_create_domain(master))) {
-                  goto out_release_master;
-          }
-
-          if (ecrt_domain_register_pdo_list(domain1,
-                                            domain1_pdos)) {
-                  goto out_release_master;
-          }
-
-          if (ecrt_master_activate(master)) {
-                  goto out_release_master;
-          }
-
-          ecrt_master_prepare(master);
-
-          requested_ticks = nano2count(TIMERTICKS);
-          tick_period = start_rt_timer(requested_ticks);
-
-          if (rt_task_init(&task, run, 0, 2000, 0, 1, NULL)) {
-                  goto out_stop_timer;
-          }
-
-          now = rt_get_time();
-          if (rt_task_make_periodic(&task, now + tick_period,
-                                    tick_period)) {
-                  goto out_stop_task;
-          }
-
-          return 0;
-
-      out_stop_task:
-          rt_task_delete(&task);
-      out_stop_timer:
-          stop_rt_timer();
-      out_deactivate:
-          ecrt_master_deactivate(master);
-      out_release_master:
-          ecrt_release_master(master);
-      out_return:
-          return -1;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 24} -- \textcircled{\tiny 25}] The
-  nanoseconds are converted to RTAI timer ticks and an RTAI timer is
-  started.  \textit{tick\_period} will be the ``real'' number of ticks
-  used for the timer period (which can be different to the requested
-  one).
-\item[\normalfont\textcircled{\tiny 27}] The RTAI task is initialized
-  by specifying the cyclic function, the parameter to hand over, the
-  stack size, priority, a flag that tells, if the function will use
-  floating point operations and a signal handler.
-\item[\normalfont\textcircled{\tiny 32}] The task is made periodic by
-  specifying a start time and a period.
-\end{description}
-
-The cleanup function of the RTAI module in listing~\ref{lst:rtaiclean}
-is nearly as simple as that of the minimal module.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI module
-    cleanup function},label={lst:rtaiclean}]
-  void __exit cleanup_mod(void)
-  {
-          rt_task_delete(&task);
-          stop_rt_timer();
-          ecrt_master_deactivate(master);
-          ecrt_release_master(master);
-          rt_sem_delete(&master_sem);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 2}] The RTAI task will be stopped
-  and deleted.
-\item[\normalfont\textcircled{\tiny 3}] After that, the RTAI timer can
-  be stopped.
-\end{description}
-
-The rest is the same as for the minimal module.
-
-Worth to mention is, that the cyclic function of the RTAI module
-(listing~\ref{lst:rtairun}) has a slightly different architecture. The
-function is not executed until returning for every cycle, but has an
-infinite loop in it, that is placed in a waiting state for the rest of
-each cycle.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI module cyclic
-    function},label={lst:rtairun}]
-  void run(long data)
-  {
-          while (1) {
-                  ecrt_master_receive(master);
-                  ecrt_domain_process(domain1);
-
-                  k_pos = EC_READ_U32(r_ssi_input);
-
-                  ecrt_master_run(master);
-                  ecrt_master_send(master);
-
-                  rt_task_wait_period();
-          }
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] The \textit{while (1)} loop
-  executes for the lifetime of the RTAI task.
-\item[\normalfont\textcircled{\tiny 12}] The
-  \textit{rt\_task\_wait\_period()} function sets the process into a
-  sleeping state until the beginning of the next cycle. It also
-  checks, if the cyclic function has to be terminated.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\section{Concurrency Example}
-\label{sec:concurrency}
-\index{Examples!Concurrency}
-
-As mentioned before, there can be concurrent access to the EtherCAT
-master. The realtime module and a EoE\index{EoE} process can compete
-for master access, for example. In this case, the module has to
-provide the locking mechanism, because it depends on the module's
-architecture which lock has to be used. The module makes this locking
-mechanism available to the master through the master's locking
-callbacks.
-
-In case of RTAI, the lock can be an RTAI semaphore, as shown in
-listing~\ref{lst:convar}. A normal linux semaphore would not be
-appropriate, because it could not block the RTAI task due to RTAI
-running in a higher domain than the linux kernel (see~\cite{rtai}).
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI semaphore for
-    concurrent access},label={lst:convar}]
-  SEM master_sem;
-\end{lstlisting}
-
-The module has to implement the two callbacks for requesting and
-releasing the master lock. An exemplary coding can be seen in
-listing~\ref{lst:conlock}.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI locking
-    callbacks for concurrent access},label={lst:conlock}]
-  int request_lock(void *data)
-  {
-          rt_sem_wait(&master_sem);
-          return 0;
-  }
-
-  void release_lock(void *data)
-  {
-          rt_sem_signal(&master_sem);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 1}] The \textit{request\_lock()}
-  function has a data parameter. The master always passes the value,
-  that was specified when registering the callback function. This can
-  be used for handing the master pointer. Notice, that it has an
-  integer return value (see line 4).
-\item[\normalfont\textcircled{\tiny 3}] The call to
-  \textit{rt\_sem\_wait()} either returns at once, when the semaphore
-  was free, or blocks until the semaphore is freed again. In any case,
-  the semaphore finally is reserved for the process calling the
-  request function.
-\item[\normalfont\textcircled{\tiny 4}] When the lock was requested
-  successfully, the function should return 0. The module can prohibit
-  requesting the lock by returning non-zero (see paragraph ``Tuning
-  the jitter'' below).
-\item[\normalfont\textcircled{\tiny 7}] The \textit{release\_lock()}
-  function gets the same argument passed, but has a void return value,
-  because is always succeeds.
-\item[\normalfont\textcircled{\tiny 9}] The \textit{rt\_sem\_signal()}
-  function frees the semaphore, that was prior reserved with
-  \textit{rt\_sem\_wait()}.
-\end{description}
-
-In the module's init function, the semaphore must be initialized, and
-the callbacks must be passed to the EtherCAT master:
-
-\begin{lstlisting}[language=C,numbers=left,caption={Module init
-    function for concurrent access},label={lst:coninit}]
-  int __init init_mod(void)
-  {
-          RTIME tick_period, requested_ticks, now;
-
-          rt_sem_init(&master_sem, 1);
-
-          if (!(master = ecrt_request_master(0))) {
-                  goto out_return;
-          }
-
-          ecrt_master_callbacks(master, request_lock,
-                                release_lock, NULL);
-          // ...
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 5}] The call to
-  \textit{rt\_sem\_init()} initializes the semaphore and sets its
-  value to 1, meaning that only one process can reserve the semaphore
-  without blocking.
-\item[\normalfont\textcircled{\tiny 11}] The callbacks are passed to
-  the master with a call to \textit{ecrt\_master\_callbacks()}. The
-  last parameter is the argument, that the master should pass with
-  each call to a callback function. Here it is not used and set to
-  \textit{NULL}.
-\end{description}
-
-For the cyclic function being only one competitor for master access,
-it has to request the lock like any other process. There is no need to
-use the callbacks (which are meant for processes of lower priority),
-so it can access the semaphore directly:
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI cyclic
-    function for concurrent access},label={lst:conrun}]
-  void run(long data)
-  {
-          while (1) {
-                  rt_sem_wait(&master_sem);
-
-                  ecrt_master_receive(master);
-                  ecrt_domain_process(domain1);
-
-                  k_pos = EC_READ_U32(r_ssi_input);
-
-                  ecrt_master_run(master);
-                  ecrt_master_send(master);
-
-                  rt_sem_signal(&master_sem);
-                  rt_task_wait_period();
-          }
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 4}] Every access to the master has
-  to be preceeded by a call to \textit{rt\_sem\_wait()}, because
-  another instance might currently access the master.
-\item[\normalfont\textcircled{\tiny 14}] When cyclic processing
-  finished, the semaphore has to be freed again, so that other
-  processes have the possibility to access the master.
-\end{description}
-
-A little change has to be made to the cleanup function in case of
-concurrent master access.
-
-\begin{lstlisting}[language=C,numbers=left,caption={RTAI module
-    cleanup function for concurrent access},label={lst:conclean}]
-  void __exit cleanup_mod(void)
-  {
-          rt_task_delete(&task);
-          stop_rt_timer();
-          ecrt_master_deactivate(master);
-          ecrt_release_master(master);
-          rt_sem_delete(&master_sem);
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 7}] Upon module cleanup, the
-  semaphore has to be deleted, so that memory can be freed.
-\end{description}
-
-\paragraph{Tuning the Jitter}
-\index{Jitter}
-
-Concurrent access leads to higher jitter of the realtime process,
-because there are situations, in which the realtime process has to
-wait for a process of lower priority to finish accessing the master.
-In most cases this is acceptable, because a master access cycle
-(receive/process/send) only takes $10$~\textmu s to $20$~\textmu s on
-recent systems, what would be the maximum additional jitter. However
-some applications demand a minimum jitter. For this reason the master
-access can be prohibited by the realtime module: If the time, another
-process wants to access the master, is to close to the beginning of
-the next realtime cycle, the module can disallow, that the lock is
-taken. In this case, the request callback has to return $1$, meaning
-that the lock has not been taken. The foreign process must abort its
-master access and try again next time.
-
-This measure helps to significantly reducing the jitter produced by
-concurrent master access. Below are exerpts of an example coding:
-
-\begin{lstlisting}[language=C,numbers=left,caption={Variables for
-    jitter reduction},label={lst:redvar}]
-  #define FREQUENCY 10000 // RTAI task frequency in Hz
-  // ...
-  cycles_t t_last_cycle = 0;
-  const cycles_t t_critical = cpu_khz * 1000 / FREQUENCY
-                              - cpu_khz * 30 / 1000;
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 3}] The variable
-  \textit{t\_last\_cycle} holds the timer ticks at the beginning of
-  the last realtime cycle.
-\item[\normalfont\textcircled{\tiny 4}] \textit{t\_critical} contains
-  the number of ticks, that may have passed since the beginning of the
-  last cycle, until there is no more foreign access possible. It is
-  calculated by substracting the ticks for $30$~\textmu s from the
-  ticks for a complete cycle.
-\end{description}
-
-\begin{lstlisting}[language=C,numbers=left,caption={Cyclic function
-    with reduced jitter},label={lst:redrun}]
-  void run(long data)
-  {
-          while (1) {
-                  t_last_cycle = get_cycles();
-                  rt_sem_wait(&master_sem);
-                  // ...
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 4}] The ticks of the beginning of
-  the current realtime cycle are taken before reserving the semaphore.
-\end{description}
-
-\begin{lstlisting}[language=C,numbers=left,caption={Request callback
-    for reduced jitter},label={lst:redreq}]
-  int request_lock(void *data)
-  {
-          // too close to the next RT cycle: deny access.
-          if (get_cycles() - t_last_cycle > t_critical)
-                  return -1;
-
-          // allow access
-          rt_sem_wait(&master_sem);
-          return 0;
-  }
-\end{lstlisting}
-
-\begin{description}
-\item[\normalfont\textcircled{\tiny 4}] If the time of request is too
-  close to the next realtime cycle (here: \textless~$30$~\textmu s
-  before the estimated beginning), the locking is denied. The
-  requesting process must abort its cycle.
-\end{description}
-
-%------------------------------------------------------------------------------
-
-\begin{thebibliography}{99}
-\bibitem{etherlab} Ingenieurgemeinschaft IgH: EtherLab -- Open Source
-  Toolkit for rapid realtime code generation under Linux with
-  Simulink/RTW and EtherCAT technology. URL: http://etherlab.org,
-  July~31, 2006.
-\bibitem{dlspec} IEC 61158-4-12: Data-link Protocol Specification.
-  International Electrotechnical Comission (IEC), 2005.
-\bibitem{alspec} IEC 61158-6-12: Application Layer Protocol
-  Specification. International Electrotechnical Comission (IEC), 2005.
-\bibitem{gpl} GNU General Public License, Version 2. URL:
-  http://www.gnu.org/licenses/gpl.txt. August~9, 2006.
-\bibitem{lsb} Linux Standard Base. URL:
-  http://www.freestandards.org/en/LSB. August~9, 2006.
-\bibitem{wireshark} Wireshark. URL: http://www.wireshark.org.
-  August~9, 2006.
-\bibitem{automata} {\it Hopcroft, J.~E. / Ullman, J.~D.}: Introduction
-  to Automata Theory, Languages and Computation. Adison-Wesley,
-  Reading, Mass.~1979.
-\bibitem{fsmmis} {\it Wagner, F. / Wolstenholme, P.}: State machine
-  misunderstandings. In: IEE journal ``Computing and Control
-  Engineering'', 2004.
-\bibitem{rtai} RTAI. The RealTime Application Interface for Linux from
-  DIAPM. URL: http://www.rtai.org, 2006.
-\end{thebibliography}
-
-\printglossary
-\addcontentsline{toc}{chapter}{\nomname}
-\markleft{\nomname}
-
-\printindex
-\markleft{Index}
-
-%------------------------------------------------------------------------------
-
-\end{document}
-
-%------------------------------------------------------------------------------




