fp@369: %------------------------------------------------------------------------------ fp@369: % fp@369: % IgH EtherCAT Master Documentation fp@369: % fp@369: % $Id$ fp@369: % fp@1630: % vi: spell spelllang=en tw=78 fp@1095: % fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \documentclass[a4paper,12pt,BCOR6mm,bibtotoc,idxtotoc]{scrbook} fp@369: fp@369: \usepackage[latin1]{inputenc} fp@369: \usepackage[automark,headsepline]{scrpage2} fp@369: \usepackage{graphicx} fp@369: \usepackage{makeidx} fp@369: \usepackage[refpage]{nomencl} fp@369: \usepackage{listings} fp@369: \usepackage{svn} fp@369: \usepackage{textcomp} fp@369: \usepackage{url} fp@1085: \usepackage{SIunits} fp@371: \usepackage[pdfpagelabels,plainpages=false]{hyperref} fp@369: fp@369: \setlength{\parskip}{0.8ex plus 0.8ex minus 0.5ex} fp@369: \setlength{\parindent}{0mm} fp@369: fp@369: \setcounter{secnumdepth}{\subsubsectionlevel} fp@369: fp@369: \DeclareFontShape{OT1}{cmtt}{bx}{n} fp@369: { fp@369: <5><6><7><8><9><10><10.95><12><14.4><17.28><20.74><24.88>cmttb10 fp@369: }{} fp@369: fp@369: \lstset{basicstyle=\ttfamily\small,numberstyle=\tiny,aboveskip=4mm, fp@1085: belowskip=2mm,escapechar=`} fp@369: \renewcommand\lstlistlistingname{List of Listings} fp@369: fp@917: % Workaround for lstlistoflistings bug fp@917: \makeatletter% --> De-TeX-FAQ fp@917: \renewcommand*{\lstlistoflistings}{% fp@917: \begingroup fp@917: \if@twocolumn fp@917: \@restonecoltrue\onecolumn fp@917: \else fp@917: \@restonecolfalse fp@917: \fi fp@917: \lol@heading fp@917: \setlength{\parskip}{\z@}% fp@917: \setlength{\parindent}{\z@}% fp@917: \setlength{\parfillskip}{\z@ \@plus 1fil}% fp@917: \@starttoc{lol}% fp@917: \if@restonecol\twocolumn\fi fp@917: \endgroup fp@917: } fp@917: \makeatother% --> \makeatletter fp@917: fp@369: \renewcommand\nomname{Glossary} fp@369: fp@369: \newcommand{\IgH}{\raisebox{-0.7667ex} fp@369: {\includegraphics[height=2.2ex]{images/ighsign}}} fp@369: fp@369: \SVN $Date$ fp@369: \SVN $Revision$ fp@369: fp@1085: \newcommand{\masterversion}{1.4.0} fp@1085: \newcommand{\linenum}[1]{\normalfont\textcircled{\tiny #1}} fp@487: fp@369: \makeindex fp@917: \makenomenclature fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \begin{document} fp@369: fp@369: \pagenumbering{roman} fp@369: \pagestyle{empty} fp@369: fp@369: \begin{titlepage} fp@369: \begin{center} fp@369: \rule{\textwidth}{1.5mm} fp@369: fp@369: {\Huge\bf IgH \includegraphics[height=2.4ex]{images/ethercat} fp@487: Master \masterversion\\[1ex] fp@1630: Preliminary Documentation} fp@369: fp@369: \vspace{1ex} fp@369: \rule{\textwidth}{1.5mm} fp@369: fp@1630: \vspace{\fill} {\Large Dipl.-Ing. (FH) Florian Pose, fp@1630: \url{fp@igh-essen.com}\\[1ex] Ingenieurgemeinschaft \IgH} fp@369: fp@369: \vspace{\fill} fp@369: {\Large Essen, \SVNDate\\[1ex] fp@369: Revision \SVNRevision} fp@369: \end{center} fp@369: \end{titlepage} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \tableofcontents fp@369: \listoftables fp@369: \listoffigures fp@1630: %\lstlistoflistings fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \newpage fp@369: \pagestyle{scrheadings} fp@369: fp@369: \section*{Conventions} fp@369: \addcontentsline{toc}{section}{Conventions} fp@369: \markleft{Conventions} fp@369: fp@369: The following typographic conventions are used: fp@369: fp@369: \begin{itemize} fp@1085: fp@1085: \item \textit{Italic face} is used for newly introduced terms and file names. fp@1085: fp@1085: \item \texttt{Typewriter face} is used for code examples and command line fp@1085: output. fp@1085: fp@1085: \item \texttt{\textbf{Bold typewriter face}} is used for user input in command fp@1085: lines. fp@1085: fp@369: \end{itemize} fp@369: fp@1085: Data values and addresses are usually specified as hexadecimal values. These fp@1085: are marked in the \textit{C} programming language style with the prefix fp@1085: \lstinline+0x+ (example: \lstinline+0x88A4+). Unless otherwise noted, address fp@1085: values are specified as byte addresses. fp@369: fp@369: Function names are always printed with parentheses, but without fp@1085: parameters. So, if a function \lstinline+ecrt_request_master()+ has fp@1085: empty parentheses, this shall not imply that it has no parameters. fp@1085: fp@1085: If shell commands have to be entered, this is marked by a dollar prompt: fp@1085: fp@1085: \begin{lstlisting} fp@1085: $ fp@369: \end{lstlisting} fp@369: fp@369: Further, if a shell command has to be entered as the superuser, the fp@1085: prompt is a mesh: fp@1085: fp@1085: \begin{lstlisting} fp@1085: # fp@369: \end{lstlisting} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \chapter{The IgH EtherCAT Master} fp@369: \label{chapter:master} fp@369: \pagenumbering{arabic} fp@369: fp@1085: This chapter covers some general information about the EtherCAT master. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \section{Feature Summary} fp@369: \label{sec:summary} fp@369: \index{Master!Features} fp@369: fp@1085: The list below gives a short summary of the master features. fp@369: fp@369: \begin{itemize} fp@1085: fp@1085: \item Designed as a kernel module for Linux 2.6. fp@1085: fp@1086: \item Implemented according to IEC 61158-12 \cite{dlspec} \cite{alspec}. fp@1086: fp@1085: \item Comes with EtherCAT-capable drivers for several common Ethernet devices. fp@1085: fp@369: \begin{itemize} fp@1085: fp@369: \item The Ethernet hardware is operated without interrupts. fp@1085: fp@1085: \item Drivers for additional Ethernet hardware can easily be implemented fp@1085: using the common device interface (see section~\ref{sec:ecdev}) provided by fp@1085: the master module. fp@1085: fp@369: \end{itemize} fp@1085: fp@1085: \item The master module supports multiple EtherCAT masters running in fp@1085: parallel. fp@1085: fp@1085: \item The master code supports any Linux realtime extension through its fp@1085: independent architecture. fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item RTAI\nomenclature{RTAI}{Realtime Application Interface}, fp@1085: ADEOS\nomenclature{ADEOS}{Adaptive Domain Environment for Operating fp@1085: Systems}, etc. fp@1085: fp@369: \item It runs well even without realtime extensions. fp@1085: fp@369: \end{itemize} fp@1085: fp@1630: \item Common ``Application Interface'' for applications, that want to use fp@1085: EtherCAT functionality (see section~\ref{sec:ecrt}). fp@1085: fp@1085: \item \textit{Domains} are introduced, to allow grouping of process fp@1085: data transfers with different slave groups and task periods. fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item Handling of multiple domains with different task periods. fp@1085: fp@1085: \item Automatic calculation of process data mapping, FMMU and sync manager fp@1085: configuration within each domain. fp@1085: fp@369: \end{itemize} fp@1085: fp@1085: \item Communication through several finite state machines. fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item Automatic bus scanning after topology changes. fp@1085: fp@1085: \item Bus monitoring during operation. fp@1085: fp@1085: \item Automatic reconfiguration of slaves (for example after power failure) fp@1085: during operation. fp@1085: fp@369: \end{itemize} fp@1085: fp@1085: \item CANopen-over-EtherCAT (CoE) fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item Sdo upload, download and information service. fp@1085: fp@1085: \item Slave configuration via Sdos. fp@1085: fp@1085: \item Sdo access from user-space and from the application. fp@1085: fp@369: \end{itemize} fp@1085: fp@1085: \item Ethernet-over-EtherCAT (EoE) fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item Transparent use of EoE slaves via virtual network interfaces. fp@1085: fp@1085: \item Natively supports either a switched or a routed EoE network fp@1085: architecture. fp@1085: fp@369: \end{itemize} fp@1085: fp@1140: \item User space command-line-tool ``ethercat`` (see fp@1140: section~\ref{sec:ethercat}) fp@1085: fp@369: \begin{itemize} fp@1085: fp@1085: \item Showing the current bus with slaves, Pdos and Sdos. fp@1085: \item Showing the bus configuration. fp@1085: \item Showing domains and process data. fp@1085: \item Setting the master's debug level. fp@1085: \item Writing alias addresses. fp@1085: \item Sdo uploading/downloading. fp@1085: \item Reading/writing a slave's SII. fp@1085: \item Setting slave states. fp@1085: \item Generate slave description XML. fp@1085: fp@369: \end{itemize} fp@1085: fp@369: \item Seamless system integration though LSB\nomenclature{LSB}{Linux fp@369: Standard Base} compliance. fp@1085: fp@369: \begin{itemize} fp@1085: fp@1095: \item Master and network device configuration via sysconfig files. fp@1085: fp@1085: \item Init script for master control. fp@1085: fp@369: \end{itemize} fp@1085: fp@369: \item Virtual read-only network interface for monitoring and debugging fp@369: purposes. fp@1085: fp@369: \end{itemize} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \section{License} fp@369: \label{sec:license} fp@369: fp@369: The master code is released under the terms and conditions of the GNU fp@369: General Public License\index{GPL} \cite{gpl} (version 2). Other fp@369: developers, that want to use EtherCAT with Linux systems, are invited fp@369: to use the master code or even participate on development. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \chapter{Architecture} fp@1085: \label{sec:arch} fp@369: \index{Master!Architecture} fp@369: fp@369: The EtherCAT master is integrated into the Linux 2.6 kernel. This was fp@1085: an early design decision, which has been made for several reasons: fp@369: fp@369: \begin{itemize} fp@1085: fp@1085: \item Kernel code has significantly better realtime characteristics, i.~e. fp@1085: less latency than user space code. It was foreseeable, that a fieldbus master fp@1085: has a lot of cyclic work to do. Cyclic work is usually triggered by timer fp@1085: interrupts inside the kernel. The execution delay of a function that processes fp@1085: timer interrupts is less, when it resides in kernel space, because there is no fp@1085: need of time-consuming context switches to a user space process. fp@1085: fp@369: \item It was also foreseeable, that the master code has to directly fp@1085: communicate with the Ethernet hardware. This has to be done in the kernel fp@1085: anyway (through network device drivers), which is one more reason for the fp@1085: master code being in kernel space. fp@1085: fp@369: \end{itemize} fp@369: fp@1085: Figure~\ref{fig:arch} gives a general overview of the master architecture. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1085: \includegraphics[width=.9\textwidth]{images/architecture} fp@369: \caption{Master architecture} fp@1085: \label{fig:arch} fp@369: \end{figure} fp@369: fp@369: \paragraph{Master Module} fp@369: \index{Master module} fp@369: fp@1086: Kernel module containing one or more EtherCAT master instances (see fp@1086: section~\ref{sec:mastermod}), the ``Device Interface'' (see fp@1630: section~\ref{sec:ecdev}) and the ``Application Interface'' (see fp@1086: section~\ref{sec:ecrt}). fp@369: fp@369: \paragraph{Device Modules} fp@369: \index{Device modules} fp@369: fp@1086: EtherCAT-capable Ethernet device driver modules\index{Device modules}, that fp@1086: offer their devices to the EtherCAT master via the device interface (see fp@1086: section~\ref{sec:ecdev}). These modified network drivers can handle network fp@1086: devices used for EtherCAT operation and ``normal'' Ethernet devices in fp@1086: parallel. A master can accept a certain device and then is able to send and fp@1086: receive EtherCAT frames. Ethernet devices declined by the master module are fp@1086: connected to the kernel's network stack as usual. fp@1085: fp@1085: \paragraph{Application Modules} fp@1086: \index{Application module} fp@1086: fp@1086: Kernel modules, that use the EtherCAT master (usually for cyclic exchange of fp@1086: process data with EtherCAT slaves). These modules are not part of the EtherCAT fp@1086: master code\footnote{Although there are some examples provided in the fp@1630: \textit{examples/} directory.}, but have to be generated or written by the fp@1630: user. An application module can ``request'' a master through the application fp@1630: interface (see section~\ref{sec:ecrt}). If this succeeds, the module has the fp@1630: control over the master: It can provide a bus configuration and exchange fp@1630: process data. fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1085: \section{Phases} fp@1085: \index{Master phases} fp@1085: fp@1086: The EtherCAT master runs through several phases (see fig.~\ref{fig:phases}): fp@1085: fp@1085: \begin{figure}[htbp] fp@1085: \centering fp@1085: \includegraphics[width=.9\textwidth]{images/phases} fp@1085: \caption{Master phases and transitions} fp@1085: \label{fig:phases} fp@1085: \end{figure} fp@1085: \begin{description} fp@1085: fp@1085: \item[Orphaned phase]\index{Orphaned phase} This mode takes effect, when the fp@1086: master still waits for its Ethernet device to connect. No bus communication is fp@1086: possible until then. fp@1086: fp@1086: \item[Idle phase]\index{Idle phase} takes effect when the master has accepted fp@1086: an Ethernet device, but is not requested by any application yet. The master fp@1085: runs its state machine (see section~\ref{sec:fsm-master}), that automatically fp@1085: scans the bus for slaves and executes pending operations from the user space fp@1085: interface (for example Sdo access). The command-line tool can be used to access fp@1085: the bus, but there is no process data exchange because of the missing bus fp@1085: configuration. fp@1085: fp@1085: \item[Operation phase]\index{Operation phase} The master is requested by an fp@1085: application that can provide a bus configuration and exchange process data. fp@1085: fp@1085: \end{description} fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1630: \section{General Behavior} % FIXME fp@1085: \index{Master behavior} fp@1085: fp@1085: \ldots fp@1085: fp@1630: % Behavior (Scanning) TODO fp@1630: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1086: \section{Master Module} fp@1630: \label{sec:mastermod} fp@1085: \index{Master module} fp@1085: fp@1086: The EtherCAT master kernel module \textit{ec\_master} can contain multiple fp@1086: master instances. Each master waits for a certain Ethernet device identified fp@1086: by its MAC address\index{MAC address}. These addresses have to be specified on fp@1086: module loading via the \textit{main\_devices} module parameter. The number of fp@1086: master instances to initialize is taken from the number of MAC addresses fp@1086: given. fp@1086: fp@1086: The below command loads the master module with a single master instance that fp@1086: waits for the Ethernet device with the MAC address fp@1086: \lstinline+00:0E:0C:DA:A2:20+. The master will be accessible via index $0$. fp@1086: fp@1086: \begin{lstlisting} fp@1086: # `\textbf{modprobe ec\_master main\_devices=00:0E:0C:DA:A2:20}` fp@1086: \end{lstlisting} fp@1086: fp@1086: MAC addresses for multiple masters have to be separated by commas: fp@1086: fp@1086: \begin{lstlisting} fp@1086: # `\textbf{modprobe ec\_master main\_devices=00:0E:0C:DA:A2:20,00:e0:81:71:d5:1c}` fp@1086: \end{lstlisting} fp@1086: fp@1086: The two masters can be addressed by their indices 0 and 1 respectively (see fp@1086: figure~\ref{fig:masters}). The master index is needed for the fp@1630: \lstinline+ecrt_master_request()+ function of the application interface (see fp@1086: section~\ref{sec:ecrt}) and the \lstinline+--master+ option of the fp@1086: \textit{ethercat} command-line tool (see section~\ref{sec:ethercat}), which fp@1086: defaults to $0$. fp@1085: fp@1085: \begin{figure}[htbp] fp@1085: \centering fp@1085: \includegraphics[width=.5\textwidth]{images/masters} fp@1085: \caption{Multiple masters in one module} fp@1085: \label{fig:masters} fp@1085: \end{figure} fp@1085: fp@1086: \paragraph{Init script} fp@1086: \index{Init script} fp@1086: fp@1086: Most probably you won't want to load the master module and the Ethernet driver fp@1086: modules manually, but start the master as a service. See fp@1086: section~\ref{sec:system} on how to do this. fp@1086: fp@1086: \paragraph{Syslog} fp@1086: fp@1086: The master module outputs information about it's state and events to the fp@1086: kernel ring buffer. These also end up in the system logs. The above module fp@1086: loading command should result in the messages below: fp@1086: fp@1086: \begin{lstlisting} fp@1086: # `\textbf{dmesg | tail -2}` fp@1086: EtherCAT: Master driver `\masterversion` fp@1086: EtherCAT: 2 masters waiting for devices. fp@1086: fp@1086: # `\textbf{tail -2 /var/log/messages}` fp@1086: Jul 4 10:22:45 ethercat kernel: EtherCAT: Master driver `\masterversion` fp@1086: Jul 4 10:22:45 ethercat kernel: EtherCAT: 2 masters waiting fp@1086: for devices. fp@1086: \end{lstlisting} fp@1086: fp@1086: All EtherCAT master output is prefixed with \lstinline+EtherCAT+ which makes fp@1086: searching the logs easier. fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1085: \section{Handling of Process Data} % FIXME fp@369: \label{sec:processdata} fp@369: fp@1085: \ldots fp@1085: fp@369: \paragraph{Process Data Image} fp@369: \index{Process data} fp@369: fp@1085: The slaves offer their inputs and outputs by presenting the master so-called fp@1085: ``Process Data Objects'' (Pdos\index{Pdo}). The available Pdos can be fp@1085: determined by reading out the slave's TXPDO and RXPDO E$^2$PROM categories. The fp@1085: application can register the Pdos for data exchange during cyclic operation. fp@1085: The sum of all registered Pdos defines the ``process data image'', which is fp@1085: exchanged via the ``Logical ReadWrite'' datagrams introduced fp@369: in~\cite[section~5.4.2.4]{dlspec}. fp@369: fp@369: \paragraph{Process Data Domains} fp@369: \index{Domain} fp@369: fp@1085: The process data image can be easily managed by creating so-called fp@814: ``domains'', which group Pdos and allocate the datagrams needed to fp@369: exchange them. Domains are mandatory for process data exchange, so fp@369: there has to be at least one. They were introduced for the following fp@369: reasons: fp@369: fp@369: \begin{itemize} fp@369: \item The maximum size of a ``Logical ReadWrite'' datagram is limited fp@369: due to the limited size of an Ethernet frame: The maximum data size fp@369: is the Ethernet data field size minus the EtherCAT frame header, fp@369: EtherCAT datagram header and EtherCAT datagram footer: $1500 - 2 - fp@369: 12 - 2 = 1484$ octets. If the size of the process data image exceeds fp@369: this limit, multiple frames have to be sent, and the image has to be fp@369: partitioned for the use of multiple datagrams. A domain manages this fp@369: automatically. fp@814: \item Not every Pdo has to be exchanged with the same frequency: The fp@814: values of Pdos can vary slowly over time (for example temperature fp@369: values), so exchanging them with a high frequency would just waste fp@369: bus bandwidth. For this reason, multiple domains can be created, to fp@814: group different Pdos and so allow separate exchange. fp@369: \end{itemize} fp@369: fp@369: There is no upper limit for the number of domains, but each domain fp@369: occupies one FMMU in each slave involved, so the maximum number of fp@369: domains is also limited by the slaves' capabilities. fp@369: fp@369: \paragraph{FMMU Configuration} fp@369: \index{FMMU!Configuration} fp@369: fp@1085: An application can register Pdos for process data exchange. Every fp@814: Pdo is part of a memory area in the slave's physical memory, that is fp@369: protected by a sync manager \cite[section~6.7]{dlspec} for fp@369: synchronized access. In order to make a sync manager react on a fp@369: datagram accessing its memory, it is necessary to access the last byte fp@369: covered by the sync manager. Otherwise the sync manager will not react fp@369: on the datagram and no data will be exchanged. That is why the whole fp@369: synchronized memory area has to be included into the process data fp@814: image: For example, if a certain Pdo of a slave is registered for fp@369: exchange with a certain domain, one FMMU will be configured to map the fp@814: complete sync-manager-protected memory, the Pdo resides in. If a fp@814: second Pdo of the same slave is registered for process data exchange fp@814: within the same domain, and this Pdo resides in the same fp@814: sync-manager-protected memory as the first Pdo, the FMMU configuration fp@369: is not touched, because the appropriate memory is already part of the fp@814: domain's process data image. If the second Pdo belongs to another fp@369: sync-manager-protected area, this complete area is also included into fp@369: the domains process data image. See figure~\ref{fig:fmmus} for an fp@369: overview, how FMMU's are configured to map physical memory to logical fp@369: process data images. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@369: \includegraphics[width=\textwidth]{images/fmmus} fp@1085: \caption{FMMU configuration for several domains} fp@369: \label{fig:fmmus} fp@369: \end{figure} fp@369: fp@1085: \paragraph{Process Data Pointers} % FIXME fp@1085: fp@1085: The figure also demonstrates the way, the application can access the exchanged fp@1085: process data: At Pdo registration, the application has to provide the address fp@1085: of a process data pointer. Upon calculation of the domain image and allocation fp@1085: of process data memory, this pointer is redirected to the appropriate location fp@1085: inside the domain's process data memory and can later be easily dereferenced by fp@1085: the module code. fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1085: \chapter{Application Interface} fp@1085: \label{sec:ecrt} fp@1085: \index{Application interface} fp@1085: fp@1630: % Interface version fp@1630: % Master Requesting and Releasing fp@1630: % Master Locking fp@1630: % Slave configuration fp@1630: % Configuring Pdo assignment and mapping fp@1630: % Domains (memory) fp@1630: % Pdo entry registration fp@1630: % Sdo configuration fp@1630: % Sdo access fp@1630: % Cyclic operation fp@1630: fp@1094: The application interface provides functions and data structures for fp@1094: applications to access and use an EtherCAT master. The complete documentation fp@1094: of the interface is included as Doxygen~\cite{doxygen} comments in the header fp@1094: file \textit{include/ecrt.h}. You can either directly view the file comments fp@1094: or generate an HTML documentation as described in section~\ref{sec:gendoc}. fp@1094: fp@1094: The following sections cover a general description of the application fp@1094: interface. fp@1094: fp@1094: Every application should use the master in two steps: fp@1094: fp@1094: \begin{description} fp@1094: fp@1094: \item[Configuration] The master is requested and the configuration is applied. fp@1094: Domains are created Slaves are configured and Pdo entries are registered (see fp@1094: section~\ref{sec:masterconfig}). fp@1094: fp@1094: \item[Operation] Cyclic code is run, process data is exchanged (see fp@1094: section~\ref{sec:cyclic}). fp@1094: fp@1094: \end{description} fp@1094: fp@1630: \paragraph{Example Applications} \index{Example Applications} There are a few fp@1630: example applications in the \textit{examples/} subdirectory of the master fp@1630: code. They are documented in the source code. fp@1630: fp@1094: %------------------------------------------------------------------------------ fp@1094: fp@1094: \section{Master Configuration} fp@1094: \label{sec:masterconfig} fp@1094: fp@1094: \ldots fp@1630: % FIXME Attaching fp@1094: fp@1094: \begin{figure}[htbp] fp@1094: \centering fp@1094: \includegraphics[width=.8\textwidth]{images/app-config} fp@1630: \caption{Master Configuration} fp@1094: \label{fig:app-config} fp@1094: \end{figure} fp@1094: fp@1094: %------------------------------------------------------------------------------ fp@1094: fp@1094: \section{Cyclic Operation} fp@1094: \label{sec:cyclic} fp@1094: fp@1094: \ldots fp@1094: % FIXME PDOS endianess fp@1094: fp@1094: fp@1094: %------------------------------------------------------------------------------ fp@1094: fp@1094: \section{Concurrent Master Access} % FIXME fp@1085: \label{sec:concurr} fp@1085: \index{Concurrency} fp@1085: fp@1085: In some cases, one master is used by several instances, for example when an fp@1085: application does cyclic process data exchange, and there are EoE-capable slaves fp@1085: that require to exchange Ethernet data with the kernel (see fp@1085: section~\ref{sec:eoeimp}). For this reason, the master is a shared resource, fp@1085: and access to it has to be sequentialized. This is usually done by locking with fp@1085: semaphores, or other methods to protect critical sections. fp@1085: fp@1085: The master itself can not provide locking mechanisms, because it has no chance fp@1630: to know the appropriate kind of lock. For example if the application uses RTAI fp@1630: functionality, ordinary kernel semaphores would not be sufficient. For that, an fp@1630: important design decision was made: The application that reserved a master must fp@1630: have the total control, therefore it has to take responsibility for providing fp@1630: the appropriate locking mechanisms. If another instance wants to access the fp@1630: master, it has to request the master lock by callbacks, that have to be set by fp@1630: the application. Moreover the application can deny access to the master if it fp@1630: considers it to be awkward at the moment. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1085: \includegraphics[width=.6\textwidth]{images/master-locks} fp@1085: \caption{Concurrent master access} fp@1085: \label{fig:locks} fp@369: \end{figure} fp@369: fp@1630: Figure~\ref{fig:locks} exemplary shows, how two processes share one master: fp@1630: The application's cyclic task uses the master for process data exchange, while fp@1630: the master-internal EoE process uses it to communicate with EoE-capable fp@1630: slaves. Both have to acquire the master lock before access: The application fp@1630: task can access the lock natively, while the EoE process has to use the fp@1630: callbacks. See the application interface documentation fp@1630: (section~\ref{sec:ecrt} of how to use the locking callbacks. fp@1630: fp@1630: %------------------------------------------------------------------------------ fp@1630: fp@1630: \chapter{Ethernet Devices} fp@1085: \label{sec:devices} fp@1085: fp@1630: The EtherCAT protocol is based on the Ethernet standard, so a master relies on fp@1630: standard Ethernet hardware to communicate with the bus. fp@1085: fp@1085: The term \textit{device} is used as a synonym for Ethernet network interface fp@1085: hardware. There are device driver modules that handle Ethernet hardware, which fp@1630: a master can use to connect to an EtherCAT bus. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{Network Driver Basics} fp@369: \label{sec:networkdrivers} fp@369: \index{Network drivers} fp@369: fp@369: EtherCAT relies on Ethernet hardware and the master needs a physical fp@369: Ethernet device to communicate with the bus. Therefore it is necessary fp@369: to understand how Linux handles network devices and their drivers, fp@369: respectively. fp@369: fp@369: \paragraph{Tasks of a Network Driver} fp@369: fp@1095: Network device drivers usually handle the lower two layers of the OSI model, fp@1095: that is the physical layer and the data-link layer. A network device itself fp@1095: natively handles the physical layer issues: It represents the hardware to fp@1095: connect to the medium and to send and receive data in the way, the physical fp@1095: layer protocol describes. The network device driver is responsible for getting fp@1095: data from the kernel's networking stack and forwarding it to the hardware, fp@1095: that does the physical transmission. If data is received by the hardware fp@1095: respectively, the driver is notified (usually by means of an interrupt) and fp@1095: has to read the data from the hardware memory and forward it to the network fp@1095: stack. There are a few more tasks, a network device driver has to handle, fp@1095: including queue control, statistics and device dependent features. fp@369: fp@369: \paragraph{Driver Startup} fp@369: fp@369: Usually, a driver searches for compatible devices on module loading. fp@369: For PCI drivers, this is done by scanning the PCI bus and checking for fp@369: known device IDs. If a device is found, data structures are allocated fp@369: and the device is taken into operation. fp@369: fp@369: \paragraph{Interrupt Operation} fp@369: \index{Interrupt} fp@369: fp@369: A network device usually provides a hardware interrupt that is used to fp@1085: notify the driver of received frames and success of transmission, or fp@369: errors, respectively. The driver has to register an interrupt service fp@369: routine (ISR\index{ISR}\nomenclature{ISR}{Interrupt Service Routine}), fp@369: that is executed each time, the hardware signals such an event. If the fp@369: interrupt was thrown by the own device (multiple devices can share one fp@369: hardware interrupt), the reason for the interrupt has to be determined fp@369: by reading the device's interrupt register. For example, if the flag fp@369: for received frames is set, frame data has to be copied from hardware fp@369: to kernel memory and passed to the network stack. fp@369: fp@1630: \paragraph{The \lstinline+net_device+ Structure} fp@369: \index{net\_device} fp@369: fp@1630: The driver registers a \lstinline+net_device+ structure for each device to fp@1630: communicate with the network stack and to create a ``network interface''. In fp@1630: case of an Ethernet driver, this interface appears as \textit{ethX}, where X is fp@1630: a number assigned by the kernel on registration. The \lstinline+net_device+ fp@1630: structure receives events (either from user space or from the network stack) fp@1630: via several callbacks, which have to be set before registration. Not every fp@1630: callback is mandatory, but for reasonable operation the ones below are needed fp@1630: in any case: fp@1630: fp@1630: \newsavebox\boxopen fp@1630: \sbox\boxopen{\lstinline+open()+} fp@1630: \newsavebox\boxstop fp@1630: \sbox\boxstop{\lstinline+stop()+} fp@1630: \newsavebox\boxxmit fp@1630: \sbox\boxxmit{\lstinline+hard_start_xmit()+} fp@1630: \newsavebox\boxstats fp@1630: \sbox\boxstats{\lstinline+get_stats()+} fp@369: fp@369: \begin{description} fp@1095: fp@1630: \item[\usebox\boxopen] This function is called when network communication has fp@1630: to be started, for example after a command \lstinline+ip link set ethX up+ from fp@1630: user space. Frame reception has to be enabled by the driver. fp@1630: fp@1630: \item[\usebox\boxstop] The purpose of this callback is to ``close'' the device, fp@1630: i.~e. make the hardware stop receiving frames. fp@1630: fp@1630: \item[\usebox\boxxmit] This function is called for each frame that has to be fp@1630: transmitted. The network stack passes the frame as a pointer to an fp@1630: \lstinline+sk_buff+ structure (``socket buffer''\index{Socket buffer}, see fp@1095: below), which has to be freed after sending. fp@1095: fp@1630: \item[\usebox\boxstats] This call has to return a pointer to the device's fp@1630: \lstinline+net_device_stats+ structure, which permanently has to be filled with fp@1095: frame statistics. This means, that every time a frame is received, sent, or an fp@1095: error happened, the appropriate counter in this structure has to be increased. fp@1095: fp@1095: \end{description} fp@1095: fp@1095: The actual registration is done with the \lstinline+register_netdev()+ call, fp@1095: unregistering is done with \lstinline+unregister_netdev()+. fp@369: fp@1630: \paragraph{The \lstinline+netif+ Interface} fp@369: \index{netif} fp@369: fp@1085: All other communication in the direction interface $\to$ network stack is done fp@1630: via the \lstinline+netif_*()+ calls. For example, on successful device opening, fp@1630: the network stack has to be notified, that it can now pass frames to the fp@1630: interface. This is done by calling \lstinline+netif_start_queue()+. After this fp@1630: call, the \lstinline+hard_start_xmit()+ callback can be called by the network fp@1630: stack. Furthermore a network driver usually manages a frame transmission queue. fp@1630: If this gets filled up, the network stack has to be told to stop passing fp@1630: further frames for a while. This happens with a call to fp@1630: \lstinline+netif_stop_queue()+. If some frames have been sent, and there is fp@1095: enough space again to queue new frames, this can be notified with fp@1095: \lstinline+netif_wake_queue()+. Another important call is fp@1095: \lstinline+netif_receive_skb()+\footnote{This function is part of the NAPI fp@1095: (``New API''), that replaces the kernel 2.4 technique for interfacing to the fp@1095: network stack (with \lstinline+netif_rx()+). NAPI is a technique to improve fp@1095: network performance on Linux. Read more in fp@1095: \url{http://www.cyberus.ca/~hadi/usenix-paper.tgz}.}: It passes a frame to the fp@1095: network stack, that was just received by the device. Frame data has to be fp@1630: included in a so-called ``socket buffer'' for that (see below). fp@369: fp@369: \paragraph{Socket Buffers} fp@369: \index{Socket buffer} fp@369: fp@1630: Socket buffers are the basic data type for the whole network stack. They serve fp@1630: as containers for network data and are able to quickly add data headers and fp@1630: footers, or strip them off again. Therefore a socket buffer consists of an fp@1095: allocated buffer and several pointers that mark beginning of the buffer fp@1630: (\lstinline+head+), beginning of data (\lstinline+data+), end of data fp@1630: (\lstinline+tail+) and end of buffer (\lstinline+end+). In addition, a socket fp@1630: buffer holds network header information and (in case of received data) a fp@1630: pointer to the \lstinline+net_device+, it was received on. There exist fp@1630: functions that create a socket buffer (\lstinline+dev_alloc_skb()+), add data fp@1630: either from front (\lstinline+skb_push()+) or back (\lstinline+skb_put()+), fp@1630: remove data from front (\lstinline+skb_pull()+) or back fp@1630: (\lstinline+skb_trim()+), or delete the buffer (\lstinline+kfree_skb()+). A fp@1630: socket buffer is passed from layer to layer, and is freed by the layer that fp@1630: uses it the last time. In case of sending, freeing has to be done by the fp@1630: network driver. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{EtherCAT Device Drivers} fp@1630: \label{sec:ethercatdrivers} fp@369: fp@1095: There are a few requirements for Ethernet network devices to function as fp@1095: EtherCAT devices, when connected to an EtherCAT bus. fp@369: fp@369: \paragraph{Dedicated Interfaces} fp@369: fp@1095: For performance and realtime purposes, the EtherCAT master needs direct and fp@1630: exclusive access to the Ethernet hardware. This implies that the network device fp@1630: must not be connected to the kernel's network stack as usual, because the fp@1630: kernel would try to use it as an ordinary Ethernet device. fp@369: fp@369: \paragraph{Interrupt-less Operation} fp@369: \index{Interrupt} fp@369: fp@1630: EtherCAT frames travel through the logical EtherCAT ring and are then sent back fp@1630: to the master. Communication is highly deterministic: A frame is sent and will fp@1630: be received again after a constant time, so there is no need to notify the fp@1630: driver about frame reception: The master can instead query the hardware for fp@1630: received frames, if it expects them to be already received. fp@1095: fp@1095: Figure~\ref{fig:interrupt} shows two workflows for cyclic frame transmission fp@1095: and reception with and without interrupts. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=.9\textwidth]{images/interrupt} fp@369: \caption{Interrupt Operation versus Interrupt-less Operation} fp@369: \label{fig:interrupt} fp@369: \end{figure} fp@369: fp@1095: In the left workflow ``Interrupt Operation'', the data from the last cycle is fp@1095: first processed and a new frame is assembled with new datagrams, which is then fp@1095: sent. The cyclic work is done for now. Later, when the frame is received fp@1095: again by the hardware, an interrupt is triggered and the ISR is executed. The fp@1095: ISR will fetch the frame data from the hardware and initiate the frame fp@1095: dissection: The datagrams will be processed, so that the data is ready for fp@1095: processing in the next cycle. fp@1095: fp@1095: In the right workflow ``Interrupt-less Operation'', there is no hardware fp@1095: interrupt enabled. Instead, the hardware will be polled by the master by fp@1095: executing the ISR. If the frame has been received in the meantime, it will be fp@1095: dissected. The situation is now the same as at the beginning of the left fp@1095: workflow: The received data is processed and a new frame is assembled and fp@1095: sent. There is nothing to do for the rest of the cycle. fp@1095: fp@1630: The interrupt-less operation is desirable, because hardware interrupts are not fp@1630: conducive in improving the driver's realtime behaviour: Their indeterministic fp@1630: incidences contribute to increasing the jitter. Besides, if a realtime fp@1630: extension (like RTAI) is used, some additional effort would have to be made to fp@1630: prioritize interrupts. fp@369: fp@369: \paragraph{Ethernet and EtherCAT Devices} fp@369: fp@1095: Another issue lies in the way Linux handles devices of the same type. For fp@1095: example, a PCI\nomenclature{PCI}{Peripheral Component Interconnect, Computer fp@1095: Bus} driver scans the PCI bus for devices it can handle. Then it registers fp@1095: itself as the responsible driver for all of the devices found. The problem is, fp@1095: that an unmodified driver can not be told to ignore a device because it will fp@1095: be used for EtherCAT later. There must be a way to handle multiple devices of fp@1095: the same type, where one is reserved for EtherCAT, while the other is treated fp@369: as an ordinary Ethernet device. fp@369: fp@1095: For all this reasons, the author decided that the only acceptable solution is fp@1095: to modify standard Ethernet drivers in a way that they keep their normal fp@1095: functionality, but gain the ability to treat one or more of the devices as fp@1095: EtherCAT-capable. fp@369: fp@369: Below are the advantages of this solution: fp@369: fp@369: \begin{itemize} fp@369: \item No need to tell the standard drivers to ignore certain devices. fp@369: \item One networking driver for EtherCAT and non-EtherCAT devices. fp@369: \item No need to implement a network driver from scratch and running fp@369: into issues, the former developers already solved. fp@369: \end{itemize} fp@369: fp@369: The chosen approach has the following disadvantages: fp@369: fp@369: \begin{itemize} fp@369: \item The modified driver gets more complicated, as it must handle fp@369: EtherCAT and non-EtherCAT devices. fp@369: \item Many additional case differentiations in the driver code. fp@1085: \item Changes and bug fixes on the standard drivers have to be ported fp@369: to the Ether\-CAT-capable versions from time to time. fp@369: \end{itemize} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{Device Selection} fp@1085: \label{sec:deviceselection} fp@369: fp@1630: After loading the master module, at least one EtherCAT-capable network driver fp@1630: module has to be loaded, that offers its devices to the master (see fp@1630: section~\ref{sec:ecdev}. The master module knows the devices to choose from the fp@1630: module parameters (see section~\ref{sec:mastermod}). If the init script is used fp@1630: to start the master, the drivers and devices to use can be specified in the fp@1630: sysconfig file (see section~\ref{sec:sysconfig}). fp@1630: fp@1630: %------------------------------------------------------------------------------ fp@1630: fp@1630: \section{EtherCAT Device Interface} fp@369: \label{sec:ecdev} fp@369: \index{Device interface} fp@369: fp@369: An anticipation to the section about the master module fp@369: (section~\ref{sec:mastermod}) has to be made in order to understand fp@369: the way, a network device driver module can connect a device to a fp@369: specific EtherCAT master. fp@369: fp@1630: The master module provides a ``device interface'' for network device drivers. fp@1630: To use this interface, a network device driver module must include the header fp@1630: \textit{devices/ecdev.h}\nomenclature{ecdev}{EtherCAT Device}, coming with the fp@1630: EtherCAT master code. This header offers a function interface for EtherCAT fp@1630: devices. All functions of the device interface are named with the prefix fp@1630: \lstinline+ecdev+. fp@1630: fp@1630: The documentation of the device interface can be found in the header file or in fp@1630: the appropriate module of the interface documentation (see fp@1630: section~\ref{sec:gendoc} for generation instructions). fp@1630: fp@1630: \ldots % FIXME general description of the device interface fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{Patching Network Drivers} fp@369: \label{sec:patching} fp@369: \index{Network drivers} fp@369: fp@1630: This section will describe, how to make a standard Ethernet driver fp@1630: EtherCAT-capable. Unfortunately, there is no standard procedure to enable an fp@1630: Ethernet driver for use with the EtherCAT master, but there are a few common fp@1630: techniques. fp@369: fp@369: \begin{enumerate} fp@1630: fp@1630: \item A first simple rule is, that \lstinline+netif_*()+ calls must be avoided fp@1630: for all EtherCAT devices. As mentioned before, EtherCAT devices have no fp@1630: connection to the network stack, and therefore must not call its interface fp@1630: functions. fp@1630: fp@1630: \item Another important thing is, that EtherCAT devices should be operated fp@1630: without interrupts. So any calls of registering interrupt handlers and enabling fp@1630: interrupts at hardware level must be avoided, too. fp@1630: fp@1630: \item The master does not use a new socket buffer for each send operation: fp@1630: Instead there is a fix one allocated on master initialization. This socket fp@1630: buffer is filled with an EtherCAT frame with every send operation and passed to fp@1630: the \lstinline+hard_start_xmit()+ callback. For that it is necessary, that the fp@1630: socket buffer is not be freed by the network driver as usual. fp@1630: fp@369: \end{enumerate} fp@369: fp@1630: An Ethernet driver usually handles several Ethernet devices, each described by fp@1630: a \lstinline+net_device+ structure with a \lstinline+priv_data+ field to fp@1630: attach driver-dependent data to the structure. To distinguish between normal fp@1630: Ethernet devices and the ones used by EtherCAT masters, the private data fp@1630: structure used by the driver could be extended by a pointer, that points to an fp@1630: \lstinline+ec_device_t+ object returned by \lstinline+ecdev_offer()+ (see fp@1630: section~\ref{sec:ecdev}) if the device is used by a master and otherwise is fp@1630: zero. fp@1630: fp@1630: The RealTek RTL-8139 Fast Ethernet driver is a ``simple'' Ethernet driver and fp@1630: can be taken as an example to patch new drivers. The interesting sections can fp@1630: be found by searching the string ``ecdev" in the file fp@1630: \textit{devices/8139too-2.6.24-ethercat.c}. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \chapter{State Machines} fp@369: \label{sec:fsm} fp@369: \index{FSM} fp@369: fp@1085: Many parts of the EtherCAT master are implemented as \textit{finite state fp@1085: machines} (FSMs\nomenclature{FSM}{Finite State Machine}). Though this leads fp@1085: to a higher grade of complexity in some aspects, is opens many new fp@1085: possibilities. fp@369: fp@369: The below short code example exemplary shows how to read all slave fp@369: states and moreover illustrates the restrictions of ``sequential'' fp@369: coding: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram fp@369: if (ec_master_simple_io(master, datagram)) return -1; fp@369: slave_states = EC_READ_U8(datagram->data); // process datagram fp@369: \end{lstlisting} fp@369: fp@1085: The \textit{ec\_master\_simple\_io()} function provides a simple interface for fp@1085: synchronously sending a single datagram and receiving the result\footnote{For fp@1085: all communication issues have been meanwhile sourced out into state machines, fp@1085: the function is deprecated and stopped existing. Nevertheless it is adequate fp@1085: for showing it's own restrictions.}. Internally, it queues the specified fp@1085: datagram, invokes the \textit{ec\_master\_send\_datagrams()} function to send fp@1085: a frame with the queued datagram and then waits actively for its reception. fp@369: fp@369: This sequential approach is very simple, reflecting in only three fp@369: lines of code. The disadvantage is, that the master is blocked for the fp@369: time it waits for datagram reception. There is no difficulty when only fp@369: one instance is using the master, but if more instances want to fp@369: (synchronously\footnote{At this time, synchronous master access will fp@369: be adequate to show the advantages of an FSM. The asynchronous fp@369: approach will be discussed in section~\ref{sec:eoeimp}}) use the fp@369: master, it is inevitable to think about an alternative to the fp@369: sequential model. fp@369: fp@369: Master access has to be sequentialized for more than one instance fp@369: wanting to send and receive datagrams synchronously. With the present fp@369: approach, this would result in having one phase of active waiting for fp@369: each instance, which would be non-acceptable especially in realtime fp@369: circumstances, because of the huge time overhead. fp@369: fp@369: A possible solution is, that all instances would be executed fp@369: sequentially to queue their datagrams, then give the control to the fp@369: next instance instead of waiting for the datagram reception. Finally, fp@369: bus IO is done by a higher instance, which means that all queued fp@369: datagrams are sent and received. The next step is to execute all fp@369: instances again, which then process their received datagrams and issue fp@369: new ones. fp@369: fp@369: This approach results in all instances having to retain their state, fp@369: when giving the control back to the higher instance. It is quite fp@369: obvious to use a \textit{finite state machine} model in this case. fp@369: Section~\ref{sec:fsmtheory} will introduce some of the theory used, fp@369: while the listings below show the basic approach by coding the example fp@369: from above as a state machine: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: // state 1 fp@369: ec_datagram_brd(datagram, 0x0130, 2); // prepare datagram fp@369: ec_master_queue(master, datagram); // queue datagram fp@369: next_state = state_2; fp@369: // state processing finished fp@369: \end{lstlisting} fp@369: fp@369: After all instances executed their current state and queued their fp@369: datagrams, these are sent and received. Then the respective next fp@369: states are executed: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: // state 2 fp@369: if (datagram->state != EC_DGRAM_STATE_RECEIVED) { fp@369: next_state = state_error; fp@369: return; // state processing finished fp@369: } fp@369: slave_states = EC_READ_U8(datagram->data); // process datagram fp@369: // state processing finished. fp@369: \end{lstlisting} fp@369: fp@369: See section~\ref{sec:statemodel} for an introduction to the fp@369: state machine programming concept used in the master code. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{State Machine Theory} fp@369: \label{sec:fsmtheory} fp@369: \index{FSM!Theory} fp@369: fp@369: A finite state machine \cite{automata} is a model of behavior with fp@369: inputs and outputs, where the outputs not only depend on the inputs, fp@369: but the history of inputs. The mathematical definition of a finite fp@369: state machine (or finite automaton) is a six-tuple $(\Sigma, \Gamma, fp@369: S, s_0, \delta, \omega)$, with fp@369: fp@369: \begin{itemize} fp@369: \item the input alphabet $\Sigma$, with $\Sigma \neq fp@369: \emptyset$, containing all input symbols, fp@369: \item the output alphabet $\Gamma$, with $\Gamma \neq fp@369: \emptyset$, containing all output symbols, fp@369: \item the set of states $S$, with $S \neq \emptyset$, fp@369: \item the set of initial states $s_0$ with $s_0 \subseteq S, s_0 \neq fp@369: \emptyset$ fp@369: \item the transition function $\delta: S \times \Sigma \rightarrow S fp@369: \times \Gamma$ fp@369: \item the output function $\omega$. fp@369: \end{itemize} fp@369: fp@369: The state transition function $\delta$ is often specified by a fp@369: \textit{state transition table}, or by a \textit{state transition fp@369: diagram}. The transition table offers a matrix view of the state fp@369: machine behavior (see table~\ref{tab:statetrans}). The matrix rows fp@369: correspond to the states ($S = \{s_0, s_1, s_2\}$) and the columns fp@369: correspond to the input symbols ($\Gamma = \{a, b, \varepsilon\}$). fp@369: The table contents in a certain row $i$ and column $j$ then represent fp@369: the next state (and possibly the output) for the case, that a certain fp@369: input symbol $\sigma_j$ is read in the state $s_i$. fp@369: fp@369: \begin{table}[htbp] fp@369: \caption{A typical state transition table} fp@369: \label{tab:statetrans} fp@369: \vspace{2mm} fp@369: \centering fp@369: \begin{tabular}{l|ccc} fp@369: & $a$ & $b$ & $\varepsilon$\\ \hline fp@369: $s_0$ & $s_1$ & $s_1$ & $s_2$\\ fp@369: $s_1$ & $s_2$ & $s_1$ & $s_0$\\ fp@369: $s_2$ & $s_0$ & $s_0$ & $s_0$\\ \hline fp@369: \end{tabular} fp@369: \end{table} fp@369: fp@369: The state diagram for the same example looks like the one in fp@369: figure~\ref{fig:statetrans}. The states are represented as circles or fp@369: ellipses and the transitions are drawn as arrows between them. Close fp@369: to a transition arrow can be the condition that must be fulfilled to fp@369: allow the transition. The initial state is marked by a filled black fp@369: circle with an arrow pointing to the respective state. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@369: \includegraphics[width=.5\textwidth]{images/statetrans} fp@369: \caption{A typical state transition diagram} fp@369: \label{fig:statetrans} fp@369: \end{figure} fp@369: fp@369: \paragraph{Deterministic and non-deterministic state machines} fp@369: fp@369: A state machine can be deterministic, meaning that for one state and fp@369: input, there is one (and only one) following state. In this case, the fp@369: state machine has exactly one starting state. Non-deterministic state fp@369: machines can have more than one transitions for a single state-input fp@369: combination. There is a set of starting states in the latter case. fp@369: fp@369: \paragraph{Moore and Mealy machines} fp@369: fp@369: There is a distinction between so-called \textit{Moore machines}, and fp@369: \textit{Mealy machines}. Mathematically spoken, the distinction lies fp@369: in the output function $\omega$: If it only depends on the current fp@369: state ($\omega: S \rightarrow \Gamma$), the machine corresponds to the fp@369: ``Moore Model''. Otherwise, if $\omega$ is a function of a state and fp@369: the input alphabet ($\omega: S \times \Sigma \rightarrow \Gamma$) the fp@369: state machine corresponds to the ``Mealy model''. Mealy machines are fp@369: the more practical solution in most cases, because their design allows fp@369: machines with a minimum number of states. In practice, a mixture of fp@369: both models is often used. fp@369: fp@369: \paragraph{Misunderstandings about state machines} fp@369: fp@1085: There is a phenomenon called ``state explosion'', that is often taken as a fp@1085: counter-argument against general use of state machines in complex environments. fp@1085: It has to be mentioned, that this point is misleading~\cite{fsmmis}. State fp@1085: explosions happen usually as a result of a bad state machine design: Common fp@1085: mistakes are storing the present values of all inputs in a state, or not fp@1085: dividing a complex state machine into simpler sub state machines. The EtherCAT fp@1085: master uses several state machines, that are executed hierarchically and so fp@1085: serve as sub state machines. These are also described below. fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1085: \section{The Master's State Model} fp@369: \label{sec:statemodel} fp@369: fp@369: This section will introduce the techniques used in the master to fp@369: implement state machines. fp@369: fp@369: \paragraph{State Machine Programming} fp@369: fp@369: There are certain ways to implement a state machine in \textit{C} fp@369: code. An obvious way is to implement the different states and actions fp@369: by one big case differentiation: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: enum {STATE_1, STATE_2, STATE_3}; fp@369: int state = STATE_1; fp@369: fp@369: void state_machine_run(void *priv_data) { fp@369: switch (state) { fp@369: case STATE_1: fp@369: action_1(); fp@369: state = STATE_2; fp@369: break; fp@369: case STATE_2: fp@369: action_2() fp@369: if (some_condition) state = STATE_1; fp@369: else state = STATE_3; fp@369: break; fp@369: case STATE_3: fp@369: action_3(); fp@369: state = STATE_1; fp@369: break; fp@369: } fp@369: } fp@369: \end{lstlisting} fp@369: fp@369: For small state machines, this is an option. The disadvantage is, that fp@369: with an increasing number of states the code soon gets complex and an fp@369: additional case differentiation is executed each run. Besides, lots of fp@369: indentation is wasted. fp@369: fp@369: The method used in the master is to implement every state in an own fp@369: function and to store the current state function with a function fp@369: pointer: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: void (*state)(void *) = state1; fp@369: fp@369: void state_machine_run(void *priv_data) { fp@369: state(priv_data); fp@369: } fp@369: fp@369: void state1(void *priv_data) { fp@369: action_1(); fp@369: state = state2; fp@369: } fp@369: fp@369: void state2(void *priv_data) { fp@369: action_2(); fp@369: if (some_condition) state = state1; fp@369: else state = state2; fp@369: } fp@369: fp@369: void state3(void *priv_data) { fp@369: action_3(); fp@369: state = state1; fp@369: } fp@369: \end{lstlisting} fp@369: fp@1085: In the master code, state pointers of all state machines\footnote{All except fp@1085: for the EoE state machine, because multiple EoE slaves have to be handled in fp@1085: parallel. For this reason each EoE handler object has its own state pointer.} fp@1630: are gathered in a single object of the \lstinline+ec_fsm_master_t+ class. This fp@1630: is advantageous, because there is always one instance of every state machine fp@1085: available and can be started on demand. fp@369: fp@369: \paragraph{Mealy and Moore} fp@369: fp@1630: If a closer look is taken to the above listing, it can be seen that the fp@1630: actions executed (the ``outputs'' of the state machine) only depend on the fp@1630: current state. This accords to the ``Moore'' model introduced in fp@1630: section~\ref{sec:fsmtheory}. As mentioned, the ``Mealy'' model offers a higher fp@1630: flexibility, which can be seen in the listing below: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: void state7(void *priv_data) { fp@369: if (some_condition) { fp@369: action_7a(); fp@369: state = state1; fp@369: } fp@369: else { fp@369: action_7b(); fp@369: state = state8; fp@369: } fp@369: } fp@369: \end{lstlisting} fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[\linenum{3} + \linenum{7}] The state function executes the actions fp@1630: depending on the state transition, that is about to be done. fp@1630: fp@369: \end{description} fp@369: fp@369: The most flexible alternative is to execute certain actions depending fp@369: on the state, followed by some actions dependent on the state fp@369: transition: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@369: void state9(void *priv_data) { fp@369: action_9(); fp@369: if (some_condition) { fp@369: action_9a(); fp@369: state = state7; fp@369: } fp@369: else { fp@369: action_9b(); fp@369: state = state10; fp@369: } fp@369: } fp@369: \end{lstlisting} fp@369: fp@1630: This model is often used in the master. It combines the best aspects of both fp@1630: approaches. fp@369: fp@369: \paragraph{Using Sub State Machines} fp@369: fp@1630: To avoid having too much states, certain functions of the EtherCAT master fp@1630: state machine have been sourced out into sub state machines. This helps to fp@1085: encapsulate the related workflows and moreover avoids the ``state explosion'' fp@1085: phenomenon described in section~\ref{sec:fsmtheory}. If the master would fp@1085: instead use one big state machine, the number of states would be a multiple of fp@1085: the actual number. This would increase the level of complexity to a fp@369: non-manageable grade. fp@369: fp@369: \paragraph{Executing Sub State Machines} fp@369: fp@369: If a state machine starts to execute a sub state machine, it usually fp@369: remains in one state until the sub state machine terminates. This is fp@369: usually done like in the listing below, which is taken out of the fp@369: slave configuration state machine code: fp@369: fp@1085: \begin{lstlisting}[gobble=2,language=C,numbers=left] fp@813: void ec_fsm_slaveconf_safeop(ec_fsm_t *fsm) fp@369: { fp@369: fsm->change_state(fsm); // execute state change fp@369: // sub state machine fp@369: fp@369: if (fsm->change_state == ec_fsm_error) { fp@369: fsm->slave_state = ec_fsm_end; fp@369: return; fp@369: } fp@369: fp@369: if (fsm->change_state != ec_fsm_end) return; fp@369: fp@369: // continue state processing fp@369: ... fp@369: \end{lstlisting} fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[\linenum{3}] \lstinline+change_state+ is the state pointer of the state fp@1630: change state machine. The state function, the pointer points on, is fp@1630: executed\ldots fp@1630: fp@1630: \item[\linenum{6}] \ldots either until the state machine terminates with the fp@1630: error state \ldots fp@1630: fp@1630: \item[\linenum{11}] \ldots or until the state machine terminates in the end fp@1630: state. Until then, the ``higher'' state machine remains in the current state fp@1630: and executes the sub state machine again in the next cycle. fp@1630: fp@369: \end{description} fp@369: fp@369: \paragraph{State Machine Descriptions} fp@369: fp@1630: The below sections describe every state machine used in the EtherCAT master. fp@1630: The textual descriptions of the state machines contain references to the fp@1630: transitions in the corresponding state transition diagrams, that are marked fp@1630: with an arrow followed by the name of the successive state. Transitions caused fp@1630: by trivial error cases (i.~e. no response from slave) are not described fp@1630: explicitly. These transitions are drawn as dashed arrows in the diagrams. fp@1630: fp@1630: %------------------------------------------------------------------------------ fp@1630: fp@1630: \section{The Master State Machine} fp@1630: \label{sec:fsm-master} fp@1630: \index{FSM!Master} fp@1630: fp@1630: The master state machine is executed in the context of the master thread. fp@1630: Figure~\ref{fig:fsm-master} shows its transition diagram. Its purposes are: fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=\textwidth]{graphs/fsm_master} fp@1630: \caption{Transition diagram of the master state machine} fp@1630: \label{fig:fsm-master} fp@369: \end{figure} fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[Bus monitoring] The bus topology is monitored. If it changes, the bus is fp@1630: (re-)scanned. fp@1630: fp@1630: \item[Slave configuration] The application-layer states of the slaves are fp@1630: monitored. If a slave is not in the state it supposed to be, the slave is fp@1630: (re-)configured. fp@1630: fp@1630: \item[Request handling] Requests (either originating from the application or fp@1630: from external sources) are handled. A request is a job that the master shall fp@1630: process asynchronously, for example an SII access, Sdo access, or similar. fp@369: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{The Slave Scan State Machine} fp@369: \label{sec:fsm-scan} fp@369: \index{FSM!Slave Scan} fp@369: fp@369: The slave scan state machine, which can be seen in fp@1630: figure~\ref{fig:fsm-slavescan}, leads through the process of reading desired fp@1630: slave information. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[height=.8\textheight]{graphs/fsm_slave_scan} fp@369: \caption{Transition diagram of the slave scan state machine} fp@369: \label{fig:fsm-slavescan} fp@369: \end{figure} fp@369: fp@1630: The scan process includes the following steps: fp@1630: fp@369: \begin{description} fp@1630: fp@1630: \item[Node Address] The node address is set for the slave, so that it can be fp@1630: node-addressed for all following operations. fp@1630: fp@1630: \item[AL State] The initial application-layer state is read. fp@1630: fp@1630: \item[Base Information] Base information (like the number of supported FMMUs) fp@1630: is read from the lower physical memory. fp@1630: fp@1630: \item[Data Link] Information about the physical ports is read. fp@1630: fp@1630: \item[SII Size] The size of the SII contents is determined to allocate SII fp@1630: image memory. fp@1630: fp@1630: \item[SII Data] The SII contents are read into the master's image. fp@1630: fp@1630: \item[PREOP] If the slave supports CoE, it is set to PREOP state using the fp@1630: State change FSM (see section~\ref{sec:fsm-change}) to enable mailbox fp@1630: communication and read the Pdo configuration via CoE. fp@1630: fp@1630: \item[Pdos] The Pdos are read via CoE (if supported) using the Pdo Reading FSM fp@1630: (see section~\ref{sec:fsm-pdo}). If this is successful, the Pdo information fp@1630: from the SII (if any) is overwritten. fp@369: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{The Slave Configuration State Machine} fp@369: \label{sec:fsm-conf} fp@369: \index{FSM!Slave Configuration} fp@369: fp@369: The slave configuration state machine, which can be seen in fp@1630: figure~\ref{fig:fsm-slaveconf}, leads through the process of configuring a fp@1630: slave and bringing it to a certain application-layer state. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[height=.9\textheight]{graphs/fsm_slave_conf} fp@369: \caption{Transition diagram of the slave configuration state fp@369: machine} fp@369: \label{fig:fsm-slaveconf} fp@369: \end{figure} fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[INIT] The state change FSM is used to bring the slave to the INIT state. fp@1630: fp@1630: \item[FMMU Clearing] To avoid that the slave reacts on any process data, the fp@1630: FMMU configuration are cleared. If the slave does not support FMMUs, this fp@1630: state is skipped. If INIT is the requested state, the state machine is fp@1630: finished. fp@1630: fp@1630: \item[Mailbox Sync Manager Configuration] If the slaves support mailbox fp@1630: communication, the mailbox sync managers are configured. Otherwise this state fp@1630: is skipped. fp@1630: fp@1630: \item[PREOP] The state change FSM is used to bring the slave to PREOP state. fp@1630: If this is the requested state, the state machine is finished. fp@1630: fp@1630: \item[Sdo Configuration] If there is a slave configuration attached (see fp@1630: section~\ref{sec:masterconfig}), and there are any Sdo configurations are fp@1630: provided by the application, these are sent to the slave. fp@1630: fp@1630: \item[Pdo Configuration] The Pdo configuration state machine is executed to fp@1630: apply all necessary Pdo configurations. fp@1630: fp@1630: \item[Pdo Sync Manager Configuration] If any Pdo sync managers exist, they are fp@1630: configured. fp@1630: fp@1630: \item[FMMU Configuration] If there are FMMUs configurations supplied by the fp@1630: application (i.~e. if the application registered Pdo entries), they are fp@1630: applied. fp@1630: fp@1630: \item[SAFEOP] The state change FSM is used to bring the slave to SAFEOP state. fp@1630: If this is the requested state, the state machine is finished. fp@1630: fp@1630: \item[OP] The state change FSM is used to bring the slave to OP state. fp@1630: If this is the requested state, the state machine is finished. fp@369: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{The State Change State Machine} fp@369: \label{sec:fsm-change} fp@369: \index{FSM!State Change} fp@369: fp@369: The state change state machine, which can be seen in fp@1630: figure~\ref{fig:fsm-change}, leads through the process of changing a slave's fp@1630: application-layer state. This implements the states and transitions described fp@1630: in \cite[section~6.4.1]{alspec}. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=.6\textwidth]{graphs/fsm_change} fp@1630: \caption{Transition Diagram of the State Change State Machine} fp@369: \label{fig:fsm-change} fp@369: \end{figure} fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[Start] The new application-layer state is requested via the ``AL Control fp@1630: Request'' register (see ~\cite[section 5.3.1]{alspec}). fp@1630: fp@1630: \item[Check for Response] Some slave need some time to respond to an AL state fp@1630: change command, and do not respond for some time. For this case, the command fp@1630: is issued again, until it is acknowledged. fp@1630: fp@1630: \item[Check AL Status] If the AL State change datagram was acknowledged, the fp@1630: ``AL Control Response'' register (see~\cite[section 5.3.2]{alspec}) must be fp@1630: read out until the slave changes the AL state. fp@1630: fp@1630: \item[AL Status Code] If the slave refused the state change command, the fp@1630: reason can be read from the ``AL Status Code'' field in the ``AL State fp@1630: Changed'' registers (see~\cite[section 5.3.3]{alspec}). fp@1630: fp@1630: \item[Acknowledge State] If the state change was not successful, the master fp@1630: has to acknowledge the old state by writing to the ``AL Control request'' fp@1630: register again. fp@1630: fp@1630: \item[Check Acknowledge] After sending the acknowledge command, it has to read fp@1630: out the ``AL Control Response'' register again. fp@369: fp@369: \end{description} fp@369: fp@1630: The ``start\_ack'' state is a shortcut in the state machine for the case, that fp@1630: the master wants to acknowledge a spontaneous AL state change, that was not fp@1630: requested. fp@1630: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{The SII State Machine} fp@369: \label{sec:fsm-sii} fp@369: \index{FSM!SII} fp@369: fp@369: The SII\index{SII} state machine (shown in figure~\ref{fig:fsm-sii}) fp@1630: implements the process of reading or writing SII data via the fp@1630: Slave Information Interface described in \cite[section~6.4]{dlspec}. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=.5\textwidth]{graphs/fsm_sii} fp@1630: \caption{Transition Diagram of the SII State Machine} fp@369: \label{fig:fsm-sii} fp@369: \end{figure} fp@369: fp@1630: This is how the reading part of the state machine works: fp@1630: fp@369: \begin{description} fp@1630: fp@1630: \item[Start Reading] The read request and the requested word address are fp@1630: written to the SII attribute. fp@1630: fp@1630: \item[Check Read Command] If the SII read request command has been fp@1630: acknowledged, a timer is started. A datagram is issued, that reads out the SII fp@1630: attribute for state and data. fp@1630: fp@1630: \item[Fetch Data] If the read operation is still busy (the SII is usually fp@1630: implemented as an E$^2$PROM), the state is read again. Otherwise the data are fp@1630: copied from the datagram. fp@1630: fp@369: \end{description} fp@369: fp@1630: The writing part works nearly similar: fp@369: fp@369: \begin{description} fp@1630: fp@1630: \item[Start Writing] A write request, the target address and the data word are fp@1630: written to the SII attribute. fp@1630: fp@1630: \item[Check Write Command] If the SII write request command has been fp@1630: acknowledged, a timer is started. A datagram is issued, that reads out the SII fp@1630: attribute for the state of the write operation. fp@1630: fp@1630: \item[Wait while Busy] If the write operation is still busy (determined by a fp@1630: minimum wait time and the state of the busy flag), the state machine remains in fp@1630: this state to avoid that another write operation is issued too early. fp@1630: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1630: \section{The Pdo State Machines} fp@1630: \label{sec:fsm-pdo} fp@1630: \index{FSM!Pdo} fp@1630: fp@1630: The Pdo state machines are a set of state machines that read or write the Pdo fp@1630: assignment and the Pdo mapping via the ``CoE Communication Area'' described in fp@1630: \cite[section 5.6.7.4]{alspec}. For the object access, the fp@1630: CANopen-over-EtherCAT access primitives are used (see fp@1630: section~\ref{sec:coeimp}), so the slave must support the CoE mailbox protocol. fp@1630: fp@1630: \paragraph{Pdo Reading FSM} This state machine (fig.~\ref{fig:fsm-pdo-read}) fp@1630: has the purpose to read the complete Pdo configuration of a slave. It reads fp@1630: the Pdo assignment for each Sync Manager and uses the Pdo Entry Reading FSM fp@1630: (fig.~\ref{fig:fsm-pdo-entry-read}) to read the mapping for each assigned Pdo. fp@1630: fp@1630: \begin{figure}[htbp] fp@1630: \centering fp@1630: \includegraphics[width=.4\textwidth]{graphs/fsm_pdo_read} fp@1630: \caption{Transition Diagram of the Pdo Reading State Machine} fp@1630: \label{fig:fsm-pdo-read} fp@1630: \end{figure} fp@1630: fp@1630: Basically it reads the every Sync manager's Pdo assignment Sdo's fp@1630: (\lstinline+0x1C1x+) number of elements to determine the number of assigned fp@1630: Pdos for this sync manager and then reads out the subindices of the Sdo to get fp@1630: the assigned Pdo's indices. When a Pdo index is read, the Pdo Entry Reading fp@1630: FSM is executed to read the Pdo's mapped Pdo entries. fp@1630: fp@1630: \paragraph{Pdo Entry Reading FSM} This state machine fp@1630: (fig.~\ref{fig:fsm-pdo-entry-read}) reads the Pdo mapping (the Pdo entries) of fp@1630: a Pdo. It reads the respective mapping Sdo (\lstinline+0x1600+ - fp@1630: \lstinline+0x17ff+, or \lstinline+0x1a00+ - \lstinline+0x1bff+) for the given fp@1630: Pdo by reading first the subindex zero (number of elements) to determine the fp@1630: number of mapped Pdo entries. After that, each subindex is read to get the fp@1630: mapped Pdo entry index, subindex and bit size. fp@1630: fp@1630: \begin{figure}[htbp] fp@1630: \centering fp@1630: \includegraphics[width=.4\textwidth]{graphs/fsm_pdo_entry_read} fp@1630: \caption{Transition Diagram of the Pdo Entry Reading State Machine} fp@1630: \label{fig:fsm-pdo-entry-read} fp@1630: \end{figure} fp@1630: fp@1630: \begin{figure}[htbp] fp@1630: \centering fp@1630: \includegraphics[width=.9\textwidth]{graphs/fsm_pdo_conf} fp@1630: \caption{Transition Diagram of the Pdo Configuration State Machine} fp@1630: \label{fig:fsm-pdo-conf} fp@1630: \end{figure} fp@1630: fp@1630: \begin{figure}[htbp] fp@1630: \centering fp@1630: \includegraphics[width=.4\textwidth]{graphs/fsm_pdo_entry_conf} fp@1630: \caption{Transition Diagram of the Pdo Entry Configuration State Machine} fp@1630: \label{fig:fsm-pdo-entry-conf} fp@1630: \end{figure} fp@1630: fp@1630: %------------------------------------------------------------------------------ fp@1630: fp@1085: \chapter{Mailbox Protocol Implementations} fp@369: \index{Mailbox} fp@369: fp@369: The EtherCAT master implements the EoE and the CoE mailbox fp@369: protocols. See the below section for details. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{Ethernet-over-EtherCAT (EoE)} fp@369: \label{sec:eoeimp} fp@369: \index{EoE} fp@369: fp@1630: The EtherCAT master implements the Ethernet-over-EtherCAT mailbox protocol to fp@1630: enable the tunneling of Ethernet frames to special slaves, that can either fp@1630: have physical Ethernet ports to forward the frames to, or have an own IP stack fp@1630: to receive the frames. fp@369: fp@369: \paragraph{Virtual Network Interfaces} fp@369: fp@1630: The master creates a virtual EoE network interface for every EoE-capable fp@1630: slave. These interfaces are called either fp@1630: fp@1630: \begin{description} fp@1630: fp@1630: \item[eoeXsY] for a slave without an alias address (see fp@1630: section~\ref{sec:alias}), where X is the master index and Y is the slave's fp@1630: ring position, or fp@1630: fp@1630: \item[eoeXaY] for a slave with a non-zero alias address, where X is the master fp@1630: index and Y is the decimal alias address. fp@1630: fp@1630: \end{description} fp@1630: fp@1630: Frames sent to these interfaces are forwarded to the associated slaves by the fp@1630: master. Frames, that are received by the slaves, are fetched by the master and fp@1630: forwarded to the virtual interfaces. fp@369: fp@369: This bears the following advantages: fp@369: fp@369: \begin{itemize} fp@1630: fp@369: \item Flexibility: The user can decide, how the EoE-capable slaves are fp@1630: interconnected with the rest of the world. fp@1630: fp@1630: \item Standard tools can be used to monitor the EoE activity and to configure fp@1630: the EoE interfaces. fp@1630: fp@1630: \item The Linux kernel's layer-2-bridging implementation (according to the fp@1630: IEEE 802.1D MAC Bridging standard) can be used natively to bridge Ethernet fp@1630: traffic between EoE-capable slaves. fp@1630: fp@1630: \item The Linux kernel's network stack can be used to route packets between fp@1630: EoE-capable slaves and to track security issues, just like having physical fp@1630: network interfaces. fp@1630: fp@369: \end{itemize} fp@369: fp@369: \paragraph{EoE Handlers} fp@369: fp@1630: The virtual EoE interfaces and the related functionality is encapsulated in fp@1630: the \lstinline+ec_eoe_t+ class. An object of this class is called ``EoE fp@1630: handler''. For example the master does not create the network interfaces fp@1630: directly: This is done inside the constructor of an EoE handler. An EoE fp@1630: handler additionally contains a frame queue. Each time, the kernel passes a fp@1630: new socket buffer for sending via the interface's fp@1630: \lstinline+hard_start_xmit()+ callback, the socket buffer is queued for fp@1630: transmission by the EoE state machine (see below). If the queue gets filled fp@1630: up, the passing of new socket buffers is suspended with a call to fp@1630: \lstinline+netif_stop_queue()+. fp@1630: fp@1630: \paragraph{Creation of EoE Handlers} fp@1630: fp@1630: During bus scanning (see section~\ref{sec:fsm-scan}), the master determines fp@1630: the supported mailbox protocols foe each slave. This is done by examining the fp@1630: ``Supported Mailbox Protocols'' mask field at word address 0x001C of the fp@1630: SII\index{SII}. If bit 1 is set, the slave supports the EoE protocol. In this fp@1630: case, an EoE handler is created for that slave. fp@369: fp@369: \paragraph{EoE State Machine} fp@369: \index{FSM!EoE} fp@369: fp@1630: Every EoE handler owns an EoE state machine, that is used to send frames to fp@1630: the corresponding slave and receive frames from the it via the EoE fp@369: communication primitives. This state machine is showed in fp@369: figure~\ref{fig:fsm-eoe}. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=.7\textwidth]{images/fsm-eoe} % FIXME fp@1630: \caption{Transition Diagram of the EoE State Machine} fp@369: \label{fig:fsm-eoe} fp@369: \end{figure} fp@369: fp@1630: % FIXME fp@1630: fp@369: \begin{description} fp@369: \item[RX\_START] The beginning state of the EoE state machine. A fp@369: mailbox check datagram is sent, to query the slave's mailbox for new fp@379: frames. $\rightarrow$~RX\_CHECK fp@369: fp@369: \item[RX\_CHECK] The mailbox check datagram is received. If the fp@369: slave's mailbox did not contain data, a transmit cycle is started. fp@379: $\rightarrow$~TX\_START fp@369: fp@369: If there are new data in the mailbox, a datagram is sent to fetch fp@379: the new data. $\rightarrow$~RX\_FETCH fp@369: fp@369: \item[RX\_FETCH] The fetch datagram is received. If the mailbox data fp@369: do not contain a ``EoE Fragment request'' command, the data are fp@369: dropped and a transmit sequence is started. fp@379: $\rightarrow$~TX\_START fp@369: fp@369: If the received Ethernet frame fragment is the first fragment, a new fp@369: socket buffer is allocated. In either case, the data are copied into fp@369: the correct position of the socket buffer. fp@369: fp@369: If the fragment is the last fragment, the socket buffer is forwarded fp@369: to the network stack and a transmit sequence is started. fp@379: $\rightarrow$~TX\_START fp@369: fp@369: Otherwise, a new receive sequence is started to fetch the next fp@379: fragment. $\rightarrow$~RX\_\-START fp@369: fp@369: \item[TX\_START] The beginning state of a transmit sequence. It is fp@1085: checked, if the transmission queue contains a frame to send. If not, fp@379: a receive sequence is started. $\rightarrow$~RX\_START fp@369: fp@369: If there is a frame to send, it is dequeued. If the queue was fp@369: inactive before (because it was full), the queue is woken up with a fp@369: call to \textit{netif\_wake\_queue()}. The first fragment of the fp@379: frame is sent. $\rightarrow$~TX\_SENT fp@369: fp@369: \item[TX\_SENT] It is checked, if the first fragment was sent fp@369: successfully. If the current frame consists of further fragments, fp@379: the next one is sent. $\rightarrow$~TX\_SENT fp@369: fp@369: If the last fragment was sent, a new receive sequence is started. fp@379: $\rightarrow$~RX\_START fp@369: \end{description} fp@369: fp@369: \paragraph{EoE Processing} fp@369: fp@1630: To execute the EoE state machine of every active EoE handler, there must be a fp@1630: cyclic process. The easiest solution would be to execute the EoE state fp@1630: machines synchronously with the master state machine (see fp@1630: section~\ref{sec:fsm-master}). This approach has the following disadvantage: fp@1630: fp@1630: Only one EoE fragment could be sent or received every few cycles. This fp@1085: causes the data rate to be very low, because the EoE state machines are not fp@1085: executed in the time between the application cycles. Moreover, the data rate fp@1085: would be dependent on the period of the application task. fp@1085: fp@1630: To overcome this problem, an own cyclic process is needed to asynchronously fp@1630: execute the EoE state machines. For that, the master owns a kernel timer, that fp@1630: is executed each timer interrupt. This guarantees a constant bandwidth, but fp@1630: poses the new problem of concurrent access to the master. The locking fp@1630: mechanisms needed for this are introduced in section~\ref{sec:concurr}. fp@369: fp@369: \paragraph{Automatic Configuration} fp@369: fp@1630: By default, slaves are left in PREOP state, if no configuration is applied. If fp@1630: an EoE interface link is set to ``up'', the requested slave's fp@1630: application-layer state is automatically set to OP. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{CANopen-over-EtherCAT (CoE)} fp@369: \label{sec:coeimp} fp@369: \index{CoE} fp@369: fp@1630: The CANopen-over-EtherCAT protocol \cite[section~5.6]{alspec} is used to fp@1630: configure slaves and exchange data objects on application level. fp@1630: fp@1630: % FIXME fp@1630: % fp@1630: % Download / Upload fp@1630: % Expedited / Normal fp@1630: % Segmenting fp@1630: % Sdo Info Services fp@1630: % fp@1630: fp@1630: \ldots fp@369: fp@814: \paragraph{Sdo Download State Machine} fp@814: fp@814: The best time to apply Sdo configurations is during the slave's PREOP fp@379: state, because mailbox communication is already possible and slave's fp@379: application will start with updating input data in the succeeding fp@814: SAFEOP state. Therefore the Sdo configuration has to be part of the fp@379: slave configuration state machine (see section~\ref{sec:fsm-conf}): It fp@814: is implemented via an Sdo download state machine, that is executed fp@813: just before entering the slave's SAFEOP state. In this way, it is fp@814: guaranteed that the Sdo configurations are applied each time, the fp@379: slave is reconfigured. fp@369: fp@814: The transition diagram of the Sdo Download state machine can be seen fp@369: in figure~\ref{fig:fsm-coedown}. fp@369: fp@369: \begin{figure}[htbp] fp@369: \centering fp@1630: \includegraphics[width=.9\textwidth]{images/fsm-coedown} % FIXME fp@369: \caption{Transition diagram of the CoE download state machine} fp@369: \label{fig:fsm-coedown} fp@369: \end{figure} fp@369: fp@1630: % FIXME fp@1630: fp@369: \begin{description} fp@369: \item[START] The beginning state of the CoE download state fp@814: machine. The ``Sdo Download Normal Request'' mailbox command is fp@379: sent. $\rightarrow$~REQUEST fp@369: fp@369: \item[REQUEST] It is checked, if the CoE download request has been fp@369: received by the slave. After that, a mailbox check command is issued fp@379: and a timer is started. $\rightarrow$~CHECK fp@369: fp@369: \item[CHECK] If no mailbox data is available, the timer is checked. fp@369: \begin{itemize} fp@814: \item If it timed out, the Sdo download is aborted. fp@379: $\rightarrow$~ERROR fp@369: \item Otherwise, the mailbox is queried again. fp@379: $\rightarrow$~CHECK fp@369: \end{itemize} fp@369: fp@369: If the mailbox contains new data, the response is fetched. fp@379: $\rightarrow$~RESPONSE fp@369: fp@369: \item[RESPONSE] If the mailbox response could not be fetched, the data fp@814: is invalid, the wrong protocol was received, or a ``Abort Sdo fp@814: Transfer Request'' was received, the Sdo download is aborted. fp@379: $\rightarrow$~ERROR fp@369: fp@814: If a ``Sdo Download Normal Response'' acknowledgement was received, fp@814: the Sdo download was successful. $\rightarrow$~END fp@814: fp@814: \item[END] The Sdo download was successful. fp@814: fp@814: \item[ERROR] The Sdo download was aborted due to an error. fp@369: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \chapter{User Space} fp@369: \label{sec:user} fp@369: \index{User space} fp@369: fp@1630: % FIXME fp@1630: fp@1630: For the master runs as a kernel module, accessing it is natively limited to fp@1630: analyzing Syslog messages and controlling using modutils. fp@1630: fp@1630: It is necessary to implement further interfaces, that make it easier to access fp@1630: the master from user space and allow a finer influence. It should be possible fp@1630: to view and to change special parameters at runtime. fp@1630: fp@1630: Bus visualization is a second point: For development and debugging purposes it fp@1630: would be nice, if one could show the connected slaves with a single command. fp@1630: fp@1630: Another aspect is automatic startup and configuration. If the master is to be fp@1630: integrated into a running system, it must be able to automatically start with fp@1630: a persistent configuration. fp@1630: fp@1630: A last thing is monitoring EtherCAT communication. For debugging purposes, fp@1630: there had to be a way to analyze EtherCAT datagrams. The best way would be fp@1630: with a popular network analyzer, like Wireshark \cite{wireshark} (the former fp@1630: Ethereal) or others. fp@1630: fp@1630: This section covers all those points and introduces the interfaces and tools fp@1630: to make all that possible. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1087: \section{Command-line Tool} fp@1087: \label{sec:ethercat} fp@1087: fp@1087: % --master fp@1087: fp@1630: \subsection{Character Devices} fp@1087: \label{sec:cdev} fp@1087: fp@1087: Each master instance will get a character device as a user-space interface. fp@1087: The devices are named \textit{/dev/EtherCATX}, where $X$ is the index of the fp@1087: master. fp@1087: fp@1087: % FIXME fp@1087: % udev fp@1087: % rights fp@1087: fp@1087: %------------------------------------------------------------------------------ fp@1087: fp@1630: \subsection{Setting Alias Addresses} fp@1630: \label{sec:alias} % FIXME fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_alias} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Displaying the Bus Configuration} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_config} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Displaying Process Data} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_data} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Setting a Master's Debug Level} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_debug} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Configured Domains} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_domains} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Master and Ethernet Devices} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_master} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Sync Managers, Pdos and Pdo Entries} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_pdos} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Sdo Dictionary} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_sdos} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Sdo Access} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_download} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_upload} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Slaves on the Bus} fp@1087: fp@1087: Slave information can be gathered with the subcommand \lstinline+slaves+: fp@1087: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_slaves} fp@1140: fp@1140: Below is a typical output: fp@1140: fp@1087: \begin{lstlisting} fp@1087: $ `\textbf{ethercat slaves}` fp@1087: 0 0:0 PREOP + EK1100 Ethernet Kopplerklemme (2A E-Bus) fp@1087: 1 5555:0 PREOP + EL3162 2K. Ana. Eingang 0-10V fp@1087: 2 5555:1 PREOP + EL4102 2K. Ana. Ausgang 0-10V fp@1087: 3 5555:2 PREOP + EL2004 4K. Dig. Ausgang 24V, 0,5A fp@1087: \end{lstlisting} fp@1087: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \subsection{SII Access} fp@1085: \label{sec:siiaccess} fp@1085: \index{SII!Access} fp@369: fp@1087: It is possible to directly read or write the complete SII contents of the fp@1087: slaves. This was introduced for the reasons below: fp@369: fp@369: \begin{itemize} fp@1087: fp@1087: \item The format of the SII data is still in development and categories can be fp@1087: added in the future. With read and write access, the complete memory contents fp@1087: can be easily backed up and restored. fp@1087: fp@1087: \item Some SII data fields have to be altered (like the alias address). A quick fp@1087: writing must be possible for that. fp@1087: fp@1087: \item Through reading access, analyzing category data is possible from user fp@1087: space. fp@1087: fp@369: \end{itemize} fp@369: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_sii_read} fp@1140: fp@1087: Reading out SII data is as easy as other commands. Though the data are in fp@1087: binary format, analysis is easier with a tool like \textit{hexdump}: fp@1087: fp@1087: \begin{lstlisting} fp@1630: $ `\textbf{ethercat sii\_read --position 3 | hexdump}` fp@1087: 0000000 0103 0000 0000 0000 0000 0000 0000 008c fp@1087: 0000010 0002 0000 3052 07f0 0000 0000 0000 0000 fp@1087: 0000020 0000 0000 0000 0000 0000 0000 0000 0000 fp@1087: ... fp@1087: \end{lstlisting} fp@1087: fp@1087: Backing up SII contents can easily done with a redirection: fp@1087: fp@1087: \begin{lstlisting} fp@1630: $ `\textbf{ethercat sii\_read --position 3 > sii-of-slave3.bin}` fp@1087: \end{lstlisting} fp@1087: fp@1087: To download SII contents to a slave, writing access to the master's character fp@1087: device is necessary (see section~\ref{sec:cdev}). fp@1087: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_sii_write} fp@1140: fp@1087: \begin{lstlisting} fp@1630: # `\textbf{ethercat sii\_write --position 3 sii-of-slave3.bin}` fp@1087: \end{lstlisting} fp@1087: fp@1087: The SII contents will be checked for validity and then sent to the slave. The fp@1087: write operation may take a few seconds. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1630: \subsection{Requesting Application-Layer States} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_states} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1630: \subsection{Generating Slave Description XML} fp@1140: fp@1140: \lstinputlisting[basicstyle=\ttfamily\footnotesize]{external/ethercat_xml} fp@1140: fp@1140: %------------------------------------------------------------------------------ fp@1140: fp@1085: \section{System Integration} fp@369: \label{sec:system} fp@369: fp@1086: To integrate the EtherCAT master as a service into a running system, it comes fp@1086: with an init script and a sysconfig file, that are described below. fp@1086: fp@1086: \subsection{Init Script} fp@369: \label{sec:init} fp@369: \index{Init script} fp@369: fp@1086: The EtherCAT master init script conforms to the requirements of the ``Linux fp@1086: Standard Base'' (LSB\index{LSB}, \cite{lsb}). The script is installed to fp@1630: \textit{etc/init.d/ethercat} below the installation prefix and has to be fp@1630: copied (or better: linked) to the appropriate location (see fp@1630: section~\ref{sec:installation}), before the master can be inserted as a fp@1630: service. Please note, that the init script depends on the sysconfig file fp@1630: described below. fp@1086: fp@1086: To provide service dependencies (i.~e. which services have to be started before fp@1086: others) inside the init script code, LSB defines a special comment block. fp@1086: System tools can extract this information to insert the EtherCAT init script at fp@1086: the correct place in the startup sequence: fp@1086: fp@1086: \lstinputlisting[firstline=38,lastline=48] fp@1086: {../script/init.d/ethercat} fp@1086: fp@1630: \subsection{Sysconfig File} fp@1086: \label{sec:sysconfig} fp@1086: \index{Sysconfig file} fp@1086: fp@1086: For persistent configuration, the init script uses a sysconfig file installed fp@1086: to \textit{etc/sysconfig/ethercat} (below the installation prefix), that is fp@1086: mandatory for the init script. The sysconfig file contains all configuration fp@1086: variables needed to operate one or more masters. The documentation is inside fp@1086: the file and included below: fp@1086: fp@1086: \lstinputlisting[numbers=left,firstline=9,basicstyle=\ttfamily\scriptsize] fp@1086: {../script/sysconfig/ethercat} fp@1086: fp@1630: \subsection{Starting the Master as a Service} fp@1086: \label{sec:service} fp@1086: \index{Service} fp@1086: fp@1086: After the init script and the sysconfig file are placed into the right fp@1086: location, the EtherCAT master can be inserted as a service. The different Linux fp@1086: distributions offer different ways to mark a service for starting and stopping fp@1086: in certain runlevels. For example, SUSE Linux provides the \textit{insserv} fp@1086: command: fp@1086: fp@1086: \begin{lstlisting} fp@1086: # `\textbf{insserv ethercat}` fp@369: \end{lstlisting} fp@369: fp@369: The init script can also be used for manually starting and stopping fp@369: the EtherCAT master. It has to be executed with one of the parameters fp@379: \texttt{start}, \texttt{stop}, \texttt{restart} or \texttt{status}. fp@369: fp@1085: \begin{lstlisting}[gobble=2] fp@379: # `\textbf{/etc/init.d/ethercat restart}` fp@369: Shutting down EtherCAT master done fp@369: Starting EtherCAT master done fp@369: \end{lstlisting} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \section{Monitoring and Debugging} fp@369: \label{sec:debug} fp@369: \index{Monitoring} fp@369: fp@1630: % FIXME fp@1630: fp@1085: For debugging purposes, every EtherCAT master registers a read-only network fp@1085: interface \textit{ecX}, where X is a number, provided by the kernel on device fp@1085: registration. While it is ``up'', the master forwards every frame sent and fp@1085: received to this interface. fp@1085: fp@1085: This makes it possible to connect an network monitor (like Wireshark or fp@1085: tcpdump) to the debug interface and monitor the EtherCAT frames. fp@1085: fp@1085: % FIXME schedule() fp@1085: It has to be considered, that can be frame rate can be very high. The master fp@1085: state machine usually runs every kernel timer interrupt (usually up to fp@1085: \unit{1}{\kilo\hertz}) and with a connected application, the rate can be even fp@369: higher. fp@369: fp@369: \paragraph{Attention:} The socket buffers needed for the operation of fp@369: the debugging interface have to be allocated dynamically. Some Linux fp@369: realtime extensions do not allow this in realtime context! fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1085: \chapter{Timing Aspects} fp@369: \label{sec:timing} fp@369: fp@1085: Although EtherCAT's timing is highly deterministic and therefore timing issues fp@1085: are rare, there are a few aspects that can (and should be) dealt with. fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@1630: \subsection{Application Interface Profiling} fp@369: \label{sec:timing-profile} fp@1630: \index{Profiling} fp@1630: % FIXME fp@369: fp@1085: One of the most important timing aspects are the execution times of the fp@1630: application interface functions, that are called in cyclic context. These fp@1085: functions make up an important part of the overall timing of the application. fp@1085: To measure the timing of the functions, the following code was used: fp@369: fp@369: \begin{lstlisting}[gobble=2,language=C] fp@369: c0 = get_cycles(); fp@369: ecrt_master_receive(master); fp@369: c1 = get_cycles(); fp@369: ecrt_domain_process(domain1); fp@369: c2 = get_cycles(); fp@369: ecrt_master_run(master); fp@369: c3 = get_cycles(); fp@369: ecrt_master_send(master); fp@369: c4 = get_cycles(); fp@369: \end{lstlisting} fp@369: fp@1085: Between each call of an interface function, the CPU timestamp counter is read. fp@1085: The counter differences are converted to \micro\second\ with help of the fp@1085: \lstinline+cpu_khz+ variable, that contains the number of increments per fp@1085: \milli\second. fp@1085: fp@1085: For the actual measuring, a system with a \unit{2.0}{\giga\hertz} CPU was used, fp@1085: that ran the above code in an RTAI thread with a period of fp@1085: \unit{100}{\micro\second}. The measuring was repeated $n = 100$ times and the fp@1085: results were averaged. These can be seen in table~\ref{tab:profile}. fp@369: fp@369: \begin{table}[htpb] fp@369: \centering fp@1630: \caption{Profiling of an Application Cycle on a \unit{2.0}{\giga\hertz} fp@1085: Processor} fp@369: \label{tab:profile} fp@369: \vspace{2mm} fp@369: \begin{tabular}{l|r|r} fp@1085: Element & Mean Duration [\second] & Standard Deviancy [\micro\second] \\ fp@369: \hline fp@369: \textit{ecrt\_master\_receive()} & 8.04 & 0.48\\ fp@369: \textit{ecrt\_domain\_process()} & 0.14 & 0.03\\ fp@369: \textit{ecrt\_master\_run()} & 0.29 & 0.12\\ fp@369: \textit{ecrt\_master\_send()} & 2.18 & 0.17\\ \hline fp@369: Complete Cycle & 10.65 & 0.69\\ \hline fp@369: \end{tabular} fp@369: \end{table} fp@369: fp@1085: It is obvious, that the functions accessing hardware make up the fp@369: lion's share. The \textit{ec\_master\_receive()} executes the ISR of fp@369: the Ethernet device, analyzes datagrams and copies their contents into fp@369: the memory of the datagram objects. The \textit{ec\_master\_send()} fp@369: assembles a frame out of different datagrams and copies it to the fp@369: hardware buffers. Interestingly, this makes up only a quarter of the fp@369: receiving time. fp@369: fp@1085: The functions that only operate on the masters internal data structures are fp@1085: very fast ($\Delta t < \unit{1}{\micro\second}$). Interestingly the runtime of fp@1085: \textit{ec\_domain\_process()} has a small standard deviancy relative to the fp@1085: mean value, while this ratio is about twice as big for fp@1085: \textit{ec\_master\_run()}: This probably results from the latter function fp@1085: having to execute code depending on the current state and the different state fp@1085: functions are more or less complex. fp@1085: fp@1085: For a realtime cycle makes up about \unit{10}{\micro\second}, the theoretical fp@1085: frequency can be up to \unit{100}{\kilo\hertz}. For two reasons, this frequency fp@369: keeps being theoretical: fp@369: fp@369: \begin{enumerate} fp@1085: fp@1085: \item The processor must still be able to run the operating system between the fp@1085: realtime cycles. fp@1085: fp@1085: \item The EtherCAT frame must be sent and received, before the next realtime fp@1085: cycle begins. The determination of the bus cycle time is difficult and covered fp@1085: in section~\ref{sec:timing-bus}. fp@1085: fp@369: \end{enumerate} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \subsection{Bus Cycle Measuring} fp@369: \label{sec:timing-bus} fp@369: \index{Bus cycle} fp@369: fp@369: For measuring the time, a frame is ``on the wire'', two timestamps fp@369: must be be taken: fp@369: fp@369: \begin{enumerate} fp@369: \item The time, the Ethernet hardware begins with physically sending fp@369: the frame. fp@369: \item The time, the frame is completely received by the Ethernet fp@369: hardware. fp@369: \end{enumerate} fp@369: fp@369: Both times are difficult to determine. The first reason is, that the fp@369: interrupts are disabled and the master is not notified, when a frame fp@369: is sent or received (polling would distort the results). The second fp@369: reason is, that even with interrupts enabled, the time from the event fp@369: to the notification is unknown. Therefore the only way to confidently fp@369: determine the bus cycle time is an electrical measuring. fp@369: fp@1630: Anyway, the bus cycle time is an important factor when designing realtime fp@1630: code, because it limits the maximum frequency for the cyclic task of the fp@1630: application. In practice, these timing parameters are highly dependent on the fp@1630: hardware and often a trial and error method must be used to determine the fp@1630: limits of the system. fp@1085: fp@1085: The central question is: What happens, if the cycle frequency is too high? The fp@1085: answer is, that the EtherCAT frames that have been sent at the end of the cycle fp@1085: are not yet received, when the next cycle starts. First this is noticed by fp@1085: \textit{ecrt\_domain\_process()}, because the working counter of the process fp@1085: data datagrams were not increased. The function will notify the user via fp@1085: Syslog\footnote{To limit Syslog output, a mechanism has been implemented, that fp@1085: outputs a summarized notification at maximum once a second.}. In this case, the fp@1085: process data keeps being the same as in the last cycle, because it is not fp@1085: erased by the domain. When the domain datagrams are queued again, the master fp@1085: notices, that they are already queued (and marked as sent). The master will fp@1085: mark them as unsent again and output a warning, that datagrams were fp@1085: ``skipped''. fp@1085: fp@1085: On the mentioned \unit{2.0}{\giga\hertz} system, the possible cycle frequency fp@1085: can be up to \unit{25}{\kilo\hertz} without skipped frames. This value can fp@1085: surely be increased by choosing faster hardware. Especially the RealTek network fp@1085: hardware could be replaced by a faster one. Besides, implementing a dedicated fp@1085: ISR for EtherCAT devices would also contribute to increasing the latency. These fp@1085: are two points on the author's to-do list. fp@1085: fp@1085: %------------------------------------------------------------------------------ fp@1085: fp@1085: \chapter{Installation} fp@1085: \label{sec:installation} fp@1085: \index{Master!Installation} fp@369: fp@1630: \section{Building the Software} fp@1094: fp@1094: The current EtherCAT master code is available at~\cite{etherlab} or can be fp@1094: obtained from the EtherLab CD. The \textit{tar.bz2} file has to be unpacked fp@1094: with the commands below (or similar): fp@369: fp@1085: \begin{lstlisting}[gobble=2] fp@1630: $ `\textbf{tar xjf ethercat-\masterversion.tar.bz2}` fp@1630: $ `\textbf{cd ethercat-\masterversion/}` fp@374: \end{lstlisting} fp@374: fp@374: The tarball was created with GNU Autotools, so the build process fp@487: follows the below commands: fp@369: fp@1085: \begin{lstlisting}[gobble=2] fp@1630: $ `\textbf{./configure}` fp@1630: $ `\textbf{make}` fp@1630: $ `\textbf{make modules}` fp@374: \end{lstlisting} fp@374: fp@1085: Table~\ref{tab:config} lists important configuration switches and options. fp@1085: fp@1085: \begin{table} fp@1085: \caption{Configuration options} fp@1085: \label{tab:config} fp@1085: \vspace{2mm} fp@1085: \begin{tabular}{l|p{.3\textwidth}|l} fp@1085: fp@1085: \bf Option/Switch & \bf Description & \bf Default\\\hline fp@1085: fp@1085: \lstinline+--prefix+ & Installation prefix & \textit{/opt/etherlab}\\ fp@1085: fp@1085: \lstinline+--with-linux-dir+ & Linux kernel sources & Use running kernel\\ fp@1085: fp@1085: \lstinline+--with-rtai-dir+ & RTAI path (only for RTAI example) & \\ fp@1085: fp@1085: \hline fp@1085: fp@1085: \lstinline+--enable-eoe+ & Enable EoE support & yes\\ fp@1085: fp@1085: \lstinline+--enable-cycles+ & Use CPU timestamp counter. Enable this on Intel fp@1085: architecture to get finer timing calculation. & no\\ fp@1085: fp@1085: \lstinline+--enable-debug-if+ & Create a debug interface for each master & no\\ fp@1085: fp@1085: \lstinline+--enable-debug-ring+ & Create a debug ring to record frames & no\\ fp@1085: fp@1085: \hline fp@1085: fp@1085: \lstinline+--enable-8139too+ & Build the 8139too driver & yes\\ fp@1085: fp@1085: \lstinline+--with-8139too-kernel+ & 8139too kernel & $\dagger$\\ fp@1085: fp@1085: \lstinline+--enable-e1000+ & Enable e1000 driver & no\\ fp@1085: fp@1085: \lstinline+--with-e1000-kernel+ & e1000 kernel & $\dagger$\\ fp@1085: fp@1085: \end{tabular} fp@1085: \vspace{2mm} fp@1085: fp@1085: \begin{description} fp@1085: fp@1085: \item[$\dagger$] If this option is not specified, the kernel version to use is fp@1085: extracted from the Linux kernel sources. fp@1085: fp@1085: \end{description} fp@1085: fp@1085: \end{table} fp@487: fp@1630: \section{Building the Interface Documentation} fp@1094: \label{sec:gendoc} fp@1094: fp@1094: The source code is documented using Doxygen~\cite{doxygen}. To build the HTML fp@1630: documentation, the Doxygen software has to be installed. The below command fp@1095: will generate the documents in the subdirectory \textit{doxygen-output}: fp@1094: fp@1094: \begin{lstlisting} fp@1094: $ `\textbf{make doc}` fp@1094: \end{lstlisting} fp@1094: fp@1630: The interface documentation can be viewed by pointing a browser to the file fp@1630: \textit{doxygen-output/html/index.html}. fp@1630: fp@1630: \section{Installing the Software} fp@1094: fp@1106: The below commands have to be entered as \textit{root}: The first one will fp@1106: install the EtherCAT header, init script, sysconfig file and the user space fp@1630: tool to the prefix path. The second one will install the kernel modules to the fp@1630: kernel's modules directory. The final \lstinline+depmod+ call is necessary to fp@1630: include the kernel modules into the \textit{modules.dep} file to make it fp@1106: available to the \lstinline+modprobe+ command, used in the init script. fp@369: fp@1094: \begin{lstlisting} fp@1106: # `\textbf{make install}` fp@1094: # `\textbf{make modules\_install}` fp@1106: # `\textbf{depmod}` fp@369: \end{lstlisting} fp@369: fp@1095: If the target kernel's modules directory is not under \textit{/lib/modules}, a fp@1095: different destination directory can be specified with the \lstinline+DESTDIR+ fp@1095: make variable. For example: fp@487: fp@1094: \begin{lstlisting} fp@1094: # `\textbf{make DESTDIR=/vol/nfs/root modules\_install}` fp@487: \end{lstlisting} fp@487: fp@487: This command will install the compiled kernel modules to fp@487: \textit{/vol/nfs/root/lib/modules}, prepended by the kernel release. fp@487: fp@1085: If the EtherCAT master shall be run as a service\footnote{Even if the EtherCAT fp@1085: master shall not be loaded on system startup, the use of the init script is fp@1086: recommended for manual (un-)loading.} (see section~\ref{sec:system}), the init fp@1086: script and the sysconfig file have to be copied (or linked) to the appropriate fp@1086: locations. The below example is suitable for SUSE Linux. It may vary for other fp@1086: distributions. fp@1085: fp@1107: % FIXME relative ln -s? fp@1094: \begin{lstlisting} fp@1094: # `\textbf{cd /opt/etherlab}` fp@1094: # `\textbf{cp etc/sysconfig/ethercat /etc/sysconfig/}` fp@1094: # `\textbf{ln -s etc/init.d/ethercat /etc/init.d/}` fp@1094: # `\textbf{insserv ethercat}` fp@374: \end{lstlisting} fp@374: fp@376: Now the sysconfig file \texttt{/etc/sysconfig/ethercat} (see fp@1085: section~\ref{sec:sysconfig}) has to be customized. The minimal customization fp@1085: is to set the \lstinline+MASTER0_DEVICE+ variable to the MAC address of the fp@1085: Ethernet device to use (or \lstinline+ff:ff:ff:ff:ff:ff+ to use the first fp@1085: device offered) and selecting the driver(s) to load via the fp@1085: \lstinline+DEVICE_MODULES+ variable. fp@369: fp@369: After the basic configuration is done, the master can be started with fp@369: the below command: fp@369: fp@1094: \begin{lstlisting} fp@1094: # `\textbf{/etc/init.d/ethercat start}` fp@369: \end{lstlisting} fp@369: fp@1630: The operation of the master can be observed with the command fp@1630: \lstinline+ethercat master+ or by viewing the Syslog\index{Syslog} fp@1630: messages, which should look like the ones below. If EtherCAT slaves are fp@1630: connected to the master's EtherCAT device, the activity indicators should fp@1630: begin to flash. fp@369: fp@369: \begin{lstlisting}[numbers=left] fp@1085: EtherCAT: Master driver `\masterversion` fp@1085: EtherCAT: 1 master waiting for devices. fp@1085: EtherCAT Intel(R) PRO/1000 Network Driver - version 6.0.60-k2 fp@1085: Copyright (c) 1999-2005 Intel Corporation. fp@1085: PCI: Found IRQ 12 for device 0000:01:01.0 fp@1085: PCI: Sharing IRQ 12 with 0000:00:1d.2 fp@1085: PCI: Sharing IRQ 12 with 0000:00:1f.1 fp@1085: EtherCAT: Accepting device 00:0E:0C:DA:A2:20 for master 0. fp@1085: EtherCAT: Starting master thread. fp@1085: ec_e1000: ec0: e1000_probe: Intel(R) PRO/1000 Network fp@1085: Connection fp@1085: ec_e1000: ec0: e1000_watchdog_task: NIC Link is Up 100 Mbps fp@1085: Full Duplex fp@1085: EtherCAT: Link state changed to UP. fp@1085: EtherCAT: 7 slave(s) responding. fp@1085: EtherCAT: Slave states: PREOP. fp@1085: EtherCAT: Scanning bus. fp@1085: EtherCAT: Bus scanning completed in 431 ms. fp@369: \end{lstlisting} fp@369: fp@369: \begin{description} fp@1085: fp@1085: \item[\linenum{1} -- \linenum{2}] The master module is loading, and one master fp@1085: is initialized. fp@1085: fp@1085: \item[\linenum{3} -- \linenum{8}] The EtherCAT-capable e1000 driver is fp@1085: loading. The master accepts the device with the address fp@1085: \lstinline+00:0E:0C:DA:A2:20+. fp@1085: fp@1085: \item[\linenum{9} -- \linenum{16}] The master goes to idle phase, starts its fp@1085: state machine and begins scanning the bus. fp@1085: fp@369: \end{description} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \begin{thebibliography}{99} fp@1094: fp@1094: \bibitem{etherlab} Ingenieurgemeinschaft IgH: EtherLab -- Open Source Toolkit fp@1094: for rapid realtime code generation under Linux with Simulink/RTW and EtherCAT fp@1094: technology. \url{http://etherlab.org/en}, 2008. fp@1094: fp@369: \bibitem{dlspec} IEC 61158-4-12: Data-link Protocol Specification. fp@1095: International Electrotechnical Commission (IEC), 2005. fp@1094: fp@1094: \bibitem{alspec} IEC 61158-6-12: Application Layer Protocol Specification. fp@1095: International Electrotechnical Commission (IEC), 2005. fp@1094: fp@1094: \bibitem{gpl} GNU General Public License, Version 2. fp@1094: \url{http://www.gnu.org/licenses/gpl.txt}. August~9, 2006. fp@1094: fp@1094: \bibitem{lsb} Linux Standard Base. fp@1094: \url{http://www.linuxfoundation.org/en/LSB}. August~9, 2006. fp@1094: fp@1094: \bibitem{wireshark} Wireshark. \url{http://www.wireshark.org}. 2008. fp@1094: fp@1094: \bibitem{automata} {\it Hopcroft, J.~E. / Ullman, J.~D.}: Introduction to fp@1094: Automata Theory, Languages and Computation. Adison-Wesley, Reading, fp@1094: Mass.~1979. fp@1094: fp@369: \bibitem{fsmmis} {\it Wagner, F. / Wolstenholme, P.}: State machine fp@1094: misunderstandings. In: IEE journal ``Computing and Control Engineering'', fp@1094: 2004. fp@1094: fp@1094: \bibitem{rtai} RTAI. The RealTime Application Interface for Linux from DIAPM. fp@1094: \url{http://www.rtai.org}, 2006. fp@1094: fp@1094: \bibitem{doxygen} Doxygen. Source code documentation generator tool. fp@1094: \url{http://www.stack.nl/~dimitri/doxygen}, 2008. fp@1094: fp@369: \end{thebibliography} fp@369: fp@917: \printnomenclature fp@369: \addcontentsline{toc}{chapter}{\nomname} fp@369: \markleft{\nomname} fp@369: fp@369: \printindex fp@369: \markleft{Index} fp@369: fp@369: %------------------------------------------------------------------------------ fp@369: fp@369: \end{document} fp@369: fp@369: %------------------------------------------------------------------------------