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%  IgH EtherCAT Master Documentation

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\newcommand{\masterversion}{1.4.0}

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%------------------------------------------------------------------------------

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\begin{document}

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\pagenumbering{roman}

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\pagestyle{empty}

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\begin{titlepage}

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  \begin{center}

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    \rule{\textwidth}{1.5mm}

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    {\Huge\bf IgH \includegraphics[height=2.4ex]{images/ethercat}

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      Master \masterversion\\[1ex]

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      Preliminary Documentation}

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    \vspace{1ex}

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    \rule{\textwidth}{1.5mm}

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    \vspace{\fill} {\Large Dipl.-Ing. (FH) Florian Pose,

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    \url{fp@igh-essen.com}\\[1ex] Ingenieurgemeinschaft \IgH}

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    \vspace{\fill}

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    {\Large Essen, \SVNDate\\[1ex]

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      Revision \SVNRevision}

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  \end{center}

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\end{titlepage}

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%------------------------------------------------------------------------------

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\tableofcontents

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\listoftables

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\section*{Conventions}

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\addcontentsline{toc}{section}{Conventions}

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\markleft{Conventions}

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The following typographic conventions are used:

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\begin{itemize}

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\item \textit{Italic face} is used for newly introduced terms and file names.

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\item \texttt{Typewriter face} is used for code examples and command line

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output.

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\item \texttt{\textbf{Bold typewriter face}} is used for user input in command

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lines.

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\end{itemize}

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Data values and addresses are usually specified as hexadecimal values. These

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are marked in the \textit{C} programming language style with the prefix

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\lstinline+0x+ (example: \lstinline+0x88A4+). Unless otherwise noted, address

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values are specified as byte addresses.

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Function names are always printed with parentheses, but without

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parameters. So, if a function \lstinline+ecrt_request_master()+ has

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empty parentheses, this shall not imply that it has no parameters.

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If shell commands have to be entered, this is marked by a dollar prompt:

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\begin{lstlisting}

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$

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Further, if a shell command has to be entered as the superuser, the

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prompt is a mesh:

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\begin{lstlisting}

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#

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%------------------------------------------------------------------------------

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\chapter{The IgH EtherCAT Master}

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\label{chapter:master}

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\pagenumbering{arabic}

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This chapter covers some general information about the EtherCAT master.

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%------------------------------------------------------------------------------

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\section{Feature Summary}

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\label{sec:summary}

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\index{Master!Features}

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The list below gives a short summary of the master features.

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\begin{itemize}

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\item Designed as a kernel module for Linux 2.6.

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\item Implemented according to IEC 61158-12 \cite{dlspec} \cite{alspec}.

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\item Comes with EtherCAT-capable drivers for several common Ethernet devices.

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  \begin{itemize}

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  \item The Ethernet hardware is operated without interrupts.

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  \item Drivers for additional Ethernet hardware can easily be implemented

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  using the common device interface (see sec.~\ref{sec:ecdev}) provided by the

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  master module.

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  \end{itemize}

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\item The master module supports multiple EtherCAT masters running in

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parallel.

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\item The master code supports any Linux realtime extension through its

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independent architecture.

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  \begin{itemize}

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  \item RTAI\nomenclature{RTAI}{Realtime Application Interface},

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  ADEOS\nomenclature{ADEOS}{Adaptive Domain Environment for Operating

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  Systems}, etc.

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  \item It runs well even without realtime extensions.

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  \end{itemize}

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\item Common ``Application Interface'' for applications, that want to use

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EtherCAT functionality (see chap.~\ref{chap:api}).

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\item \textit{Domains} are introduced, to allow grouping of process

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  data transfers with different slave groups and task periods.

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  \begin{itemize}

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  \item Handling of multiple domains with different task periods.

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  \item Automatic calculation of process data mapping, FMMU and sync manager

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  configuration within each domain.

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  \end{itemize}

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\item Communication through several finite state machines.

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  \begin{itemize}

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  \item Automatic bus scanning after topology changes.

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  \item Bus monitoring during operation.

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  \item Automatic reconfiguration of slaves (for example after power failure)

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  during operation.

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  \end{itemize}

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  \begin{itemize}

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  \end{itemize}

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  \begin{itemize}

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  \item Transparent use of EoE slaves via virtual network interfaces.

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  \item Natively supports either a switched or a routed EoE network

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  architecture.

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  \end{itemize}

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\item Userspace command-line-tool ``ethercat`` (see sec.~\ref{sec:tool})

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  \begin{itemize}

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  \item Showing the bus configuration.

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  \item Showing domains and process data.

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  \item Setting the master's debug level.

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  \item Writing alias addresses.

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  \item Reading/writing a slave's SII.

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  \item Setting slave states.

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  \item Generate slave description XML.

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  \end{itemize}

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\item Seamless system integration though LSB\nomenclature{LSB}{Linux

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    Standard Base} compliance.

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  \begin{itemize}

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  \item Master and network device configuration via sysconfig files.

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  \item Init script for master control.

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  \end{itemize}

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\item Virtual read-only network interface for monitoring and debugging

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  purposes.

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\end{itemize}

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%------------------------------------------------------------------------------

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\section{License}

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\label{sec:license}

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The master code is released under the terms and conditions of the GNU General

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Public License (GPL \cite{gpl})\index{GPL}, version 2. Other developers, that

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want to use EtherCAT with Linux systems, are invited to use the master code or

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even participate on development.

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%------------------------------------------------------------------------------

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\chapter{Architecture}

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\label{sec:arch}

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\index{Master!Architecture}

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The EtherCAT master is integrated into the Linux 2.6 kernel. This was

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an early design decision, which has been made for several reasons:

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\begin{itemize}

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\item Kernel code has significantly better realtime characteristics, i.\,e.\

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less latency than userspace code. It was foreseeable, that a fieldbus master

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has a lot of cyclic work to do. Cyclic work is usually triggered by timer

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interrupts inside the kernel. The execution delay of a function that processes

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timer interrupts is less, when it resides in kernelspace, because there is no

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need of time-consuming context switches to a userspace process.

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\item It was also foreseeable, that the master code has to directly

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communicate with the Ethernet hardware. This has to be done in the kernel

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anyway (through network device drivers), which is one more reason for the

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master code being in kernelspace.

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\end{itemize}

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Figure~\ref{fig:arch} gives a general overview of the master architecture.

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\begin{figure}[htbp]

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  \centering

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  \includegraphics[width=.9\textwidth]{images/architecture}

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  \caption{Master Architecture}

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  \label{fig:arch}

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\end{figure}

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The components of the master environment are described below:

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\begin{description}

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\item[Master Module]\index{Master Module} Kernel module containing one or more

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EtherCAT master instances (see sec.~\ref{sec:mastermod}), the ``Device

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Interface'' (see sec.~\ref{sec:ecdev}) and the ``Application Interface'' (see

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chap.~\ref{chap:api}).

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\item[Device Modules]\index{Device modules} EtherCAT-capable Ethernet device

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driver modules\index{Device modules}, that offer their devices to the EtherCAT

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master via the device interface (see sec.~\ref{sec:ecdev}). These modified

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network drivers can handle network devices used for EtherCAT operation and

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``normal'' Ethernet devices in parallel. A master can accept a certain device

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and then is able to send and receive EtherCAT frames. Ethernet devices

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declined by the master module are connected to the kernel's network stack as

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usual.

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\item[Application Modules]\index{Application} A kernel module that uses the

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EtherCAT master (usually for cyclic exchange of process data with EtherCAT

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slaves). These modules are not part of the EtherCAT master

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code\footnote{Although there are some examples provided in the

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\textit{examples/} directory.}, but have to be generated or written by the

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user. An application module can ``request'' a master through the application

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interface (see chap.~\ref{chap:api}). If this succeeds, it has the control

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over the master: It can provide a bus configuration and exchange process data.

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\end{description}

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%------------------------------------------------------------------------------

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\section{Master Module}

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\label{sec:mastermod}

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\index{Master module}

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The EtherCAT master kernel module \textit{ec\_master} can contain multiple

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master instances. Each master waits for a certain Ethernet device identified

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by its MAC address\index{MAC address}. These addresses have to be specified on

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module loading via the \textit{main\_devices} module parameter. The number of

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master instances to initialize is taken from the number of MAC addresses

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given.

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The below command loads the master module with a single master instance that

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waits for the Ethernet device with the MAC address

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\lstinline+00:0E:0C:DA:A2:20+. The master will be accessible via index $0$.

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\begin{lstlisting}

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# `\textbf{modprobe ec\_master main\_devices=00:0E:0C:DA:A2:20}`

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\end{lstlisting}

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MAC addresses for multiple masters have to be separated by commas:

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\begin{lstlisting}

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# `\textbf{modprobe ec\_master main\_devices=00:0E:0C:DA:A2:20,00:e0:81:71:d5:1c}`

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\end{lstlisting}

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The two masters can be addressed by their indices 0 and 1 respectively (see

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figure~\ref{fig:masters}). The master index is needed for the

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\lstinline+ecrt_master_request()+ function of the application interface (see

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chap.~\ref{chap:api}) and the \lstinline+--master+ option of the

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\textit{ethercat} command-line tool (see sec.~\ref{sec:tool}), which defaults

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to $0$.

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\begin{figure}[htbp]

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  \centering

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  \includegraphics[width=.5\textwidth]{images/masters}

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  \caption{Multiple masters in one module}

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  \label{fig:masters}

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\end{figure}

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\paragraph{Init Script}

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\index{Init script}

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In most cases it is not necessary to load the master module and the Ethernet

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driver modules manually. There is an init script available, so the master can

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be started as a service (see sec.~\ref{sec:system}).

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\paragraph{Syslog}

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The master module outputs information about its state and events to the kernel

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ring buffer. These also end up in the system logs.  The above module loading

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command should result in the messages below:

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\begin{lstlisting}

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# `\textbf{dmesg | tail -2}`

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EtherCAT: Master driver `\masterversion`

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EtherCAT: 2 masters waiting for devices.

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# `\textbf{tail -2 /var/log/messages}`

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Jul  4 10:22:45 ethercat kernel: EtherCAT: Master driver `\masterversion`

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Jul  4 10:22:45 ethercat kernel: EtherCAT: 2 masters waiting

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                                 for devices.

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\end{lstlisting}

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All EtherCAT master output is prefixed with \lstinline+EtherCAT+ which makes

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searching the logs easier.

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%------------------------------------------------------------------------------

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\section{Master Phases}

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\index{Master phases}

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Every EtherCAT master provided by the master module (see

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sec.~\ref{sec:mastermod}) runs through several phases (see

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fig.~\ref{fig:phases}):

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\begin{figure}[htbp]

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  \centering

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  \includegraphics[width=.9\textwidth]{images/phases}

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  \caption{Master phases and transitions}

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  \label{fig:phases}

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\end{figure}

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\begin{description}

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\item[Orphaned phase]\index{Orphaned phase} This mode takes effect, when the

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master still waits for its Ethernet device to connect. No bus communication is

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possible until then.

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\item[Idle phase]\index{Idle phase} takes effect when the master has accepted

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an Ethernet device, but is not requested by any application yet. The master

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runs its state machine (see sec.~\ref{sec:fsm-master}), that automatically

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scans the bus for slaves and executes pending operations from the userspace

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access the bus, but there is no process data exchange because of the missing

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bus configuration.

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\item[Operation phase]\index{Operation phase} The master is requested by an

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application that can provide a bus configuration and exchange process data.

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\end{description}

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%------------------------------------------------------------------------------

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\section{Process Data}

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\label{sec:processdata}

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This section shall introduce a few terms and ideas how the master handles

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process data.

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\paragraph{Process Data Image}

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\index{Process data}

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Slaves offer their inputs and outputs by presenting the master so-called

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determined by reading out the slave's TXPDO and RXPDO SII categories from the

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objects (see sec.~\ref{sec:coe}), if available.  The application can register

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via datagrams with ``logical'' memory access (like LWR, LRD or LRW) introduced

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in~\cite[sec.~5.4]{dlspec}.

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\paragraph{Process Data Domains}

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\index{Domain}

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The process data image can be easily managed by creating so-called

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process data exchange, so there has to be at least one. They were introduced

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for the following reasons:

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\begin{itemize}

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\item The maximum size of a datagram is limited due to the limited size of an

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Ethernet frame: The maximum data size is the Ethernet data field size minus

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the EtherCAT frame header, EtherCAT datagram header and EtherCAT datagram

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footer: $1500 - 2 - 12 - 2 = 1484$ octets. If the size of the process data

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image exceeds this limit, multiple frames have to be sent, and the image has