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%  IgH EtherCAT Master Documentation

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\begin{document}

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\pagenumbering{roman}

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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\sf\textbf{IgH \includegraphics[height=2.4ex]{images/ethercat}

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      Master \masterversion}\\[1ex]

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      \textbf{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, \rcsInfoLongDate\\[1ex]

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      Revision \rcsInfoRevision}

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

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

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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 / 3.x.

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

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

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chips, as well as a generic driver for all chips supported by the Linux

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kernel.

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  \begin{itemize}

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  \item The native drivers operate the hardware without interrupts.

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  \item Native drivers for additional Ethernet hardware can easily be

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  implemented using the common device interface (see~\autoref{sec:ecdev})

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  provided by the master module.

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  \item For any other hardware, the generic driver can be used. It uses the

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  lower layers of the Linux network stack.

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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} \cite{rtai}

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  (including LXRT via RTDM), ADEOS\nomenclature{ADEOS}{Adaptive Domain

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  Environment for Operating Systems}, RT-Preempt \cite{rt-preempt}, Xenomai

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  (including RTDM), 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 \autoref{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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\item Distributed Clocks support (see \autoref{sec:dc}).

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  \begin{itemize}

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  \item Configuration of the slave's DC parameters through the application

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  interface.

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  \item Synchronization (offset and drift compensation) of the distributed

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  slave clocks to the reference clock.

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  \item Optional synchronization of the reference clock to the master clock or

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  the other way round.

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  \end{itemize}

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\item CANopen over EtherCAT (CoE)

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  \begin{itemize}

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  \item SDO upload, download and information service.

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  \item Slave configuration via SDOs.

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  \item SDO access from userspace and from the application.

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  \end{itemize}

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\item Ethernet over EtherCAT (EoE)

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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 Vendor-specific over EtherCAT (VoE)

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  \begin{itemize}

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  \item Communication with vendor-specific mailbox protocols via the API.

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  \end{itemize}

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\item File Access over EtherCAT (FoE)

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  \begin{itemize}

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  \item Loading and storing files via the command-line tool.

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  \item Updating a slave's firmware can be done easily.

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  \end{itemize}

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\item Servo Profile over EtherCAT (SoE)

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  \begin{itemize}

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  \item Implemented according to IEC 61800-7 \cite{soespec}.

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  \item Storing IDN configurations, that are written to the slave during

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  startup.

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  \item Accessing IDNs via the command-line tool.

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  \item Accessing IDNs at runtime via the the user-space library.

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  \end{itemize}

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\item Userspace command-line-tool ``ethercat'' (see \autoref{sec:tool})

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  \begin{itemize}

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  \item Detailed information about master, slaves, domains and bus

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  configuration.

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  \item Setting the master's debug level.

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  \item Reading/Writing alias addresses.

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  \item Listing slave configurations.

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  \item Viewing process data.

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  \item SDO download/upload; listing SDO dictionaries.

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  \item Loading and storing files via FoE.

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  \item SoE IDN access.

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  \item Access to slave registers.

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  \item Slave SII (EEPROM) access.

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  \item Controlling application-layer states.

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  \item Generation of slave description XML and C-code from existing slaves.

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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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  \item Service file for systemd.

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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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To allow static linking of userspace application against the master's

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application interface (see \autoref{chap:api}), the userspace library (see

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\autoref{sec:userlib}) is licensed under the terms and conditions of the GNU

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Lesser General Public License (LGPL \cite{lgpl})\index{LGPL}, version 2.1.

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

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\chapter{Architecture}

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\label{chap:arch}

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\index{Master!Architecture}

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

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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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\autoref{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=\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 \autoref{sec:mastermod}), the ``Device

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Interface'' (see \autoref{sec:ecdev}) and the ``Application Interface'' (see

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\autoref{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 \autoref{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]\index{Application} A program that uses the EtherCAT master

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(usually for cyclic exchange of process data with EtherCAT slaves). These

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programs are not part of the EtherCAT master code\footnote{Although there are

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some examples provided in the \textit{examples/} directory.}, but have to be

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generated or written by the user. An application can request a master through

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the application interface (see \autoref{chap:api}). If this succeeds, it has

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the control over the master: It can provide a bus configuration and exchange

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process data.  Applications can be kernel modules (that use the kernel

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application interface directly) or userspace programs, that use the

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application interface via the EtherCAT library (see \autoref{sec:userlib}), or

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the RTDM library (see~\autoref{sec:rtdm}).

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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 certain Ethernet device(s) identified

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by its MAC address(es)\index{MAC address}. These addresses have to be

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specified on module loading via the \textit{main\_devices} (and optional:

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\textit{backup\_devices}) module parameter.  The number of master instances to

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initialize is taken from the number of MAC addresses given.

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

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waits for one 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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\autoref{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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\autoref{chap:api}) and the \lstinline+--master+ option of the

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\textit{ethercat} command-line tool (see \autoref{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{Debug Level} The master module also has a parameter

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\textit{debug\_level} to set the initial debug level for all masters (see

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also~\autoref{sec:ethercat-debug}).

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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 \autoref{sec:system}). For systems that are

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managed by systemd \cite{systemd}, there is also a service file available.

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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.