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<!-- Copyright (C) 2002 Free Software Foundation, Inc. -->
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<!-- This material may be distributed only subject to the terms -->
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<!-- and conditions set forth in the Open Publication License, v1.0 -->
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<!-- or later (the latest version is presently available at -->
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<!-- http://www.opencontent.org/openpub/). -->
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<!-- Distribution of the work or derivative of the work in any -->
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<!-- standard (paper) book form is prohibited unless prior -->
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<!-- permission is obtained from the copyright holder. -->
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<HTML
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><HEAD
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><TITLE
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>Synthetic Target Watchdog Device</TITLE
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"></HEAD
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><BODY
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><H1
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><A
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NAME="DEVS-WATCHDOG-SYNTH">Synthetic Target Watchdog Device</H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN4"
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></A
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><H2
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>Name</H2
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>Synthetic Target Watchdog Device -- Emulate watchdog hardware in the synthetic target</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN7"
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></A
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><H2
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>Overview</H2
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><P
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>Some target hardware comes equipped with a watchdog timer. Application
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code can start this timer and after a certain period of time,
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typically a second, the watchdog will trigger. Usually this causes the
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hardware to reboot. The application can prevent this by regularly
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resetting the watchdog. An automatic reboot can be very useful when
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deploying hardware in the field: a hardware glitch could cause the
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unit to hang; or the software could receive an unexpected sequence of
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inputs, never seen in the laboratory, causing the system to lock up.
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Often the hardware is still functional, and a reboot sorts out the
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problem with only a brief interruption in service.
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</P
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><P
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>The synthetic target watchdog package emulates watchdog hardware.
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During system initialization watchdog device will be instantiated,
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and the <TT
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CLASS="FILENAME"
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>watchdog.tcl</TT
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> script will be loaded by the
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I/O auxiliary. When the eCos application starts the watchdog device,
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the <TT
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CLASS="FILENAME"
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>watchdog.tcl</TT
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> script will start checking the
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state of the eCos application at one second intervals. A watchdog
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reset call simply involves a message to the I/O auxiliary. If the
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<TT
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CLASS="FILENAME"
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>watchdog.tcl</TT
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> script detects that a second has
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<A
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HREF="devs-watchdog-synth.html#SYNTH-WATCHDOG-WALLCLOCK-ELAPSED"
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>elapsed</A
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>
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without a reset then it will send a <TT
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CLASS="LITERAL"
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>SIGPWR</TT
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> signal
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to the eCos application, causing the latter to terminate. If gdb is
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being used to run the application, the user will get a chance to
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investigate what is happening. This behaviour is different from real
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hardware in that there is no automatic reboot, but the synthetic
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target is used only for development purposes, not deployment in the
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field: if a reboot is desired then this can be achieved very easily
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by using gdb commands to run another instance of the application.
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</P
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="DEVS-WATCHDOG-SYNTH-INSTALL"
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></A
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><H2
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>Installation</H2
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><P
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>Before a synthetic target eCos application can use a watchdog device
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it is necessary to build and install host-side support. The relevant
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code resides in the <TT
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CLASS="FILENAME"
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>host</TT
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>
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subdirectory of the synthetic target watchdog package, and building it
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involves the standard <B
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CLASS="COMMAND"
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>configure</B
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>,
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<B
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CLASS="COMMAND"
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>make</B
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> and <B
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CLASS="COMMAND"
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>make install</B
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> steps. The
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implementation of the watchdog support does not require any
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executables, just a Tcl script <TT
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CLASS="FILENAME"
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>watchdog.tcl</TT
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> and
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some support files, so the <B
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CLASS="COMMAND"
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>make</B
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> step is a no-op.
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</P
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><P
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>There are two main ways of building the host-side software. It is
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possible to build both the generic host-side software and all
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package-specific host-side software, including the watchdog support,
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in a single build tree. This involves using the
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<B
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CLASS="COMMAND"
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>configure</B
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> script at the toplevel of the eCos
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repository. For more information on this, see the
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<TT
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CLASS="FILENAME"
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>README.host</TT
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> file at the top of the repository.
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Note that if you have an existing build tree which does not include
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the synthetic target watchdog support then it will be necessary to
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rerun the toplevel configure script: the search for appropriate
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packages happens at configure time.
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</P
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><P
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>The alternative is to build just the host-side for this package.
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This requires a separate build directory, building directly in the
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source tree is disallowed. The <B
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CLASS="COMMAND"
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>configure</B
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> options
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are much the same as for a build from the toplevel, and the
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<TT
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CLASS="FILENAME"
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>README.host</TT
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> file can be consulted for more
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details. It is essential that the watchdog support be configured with
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the same <TT
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CLASS="OPTION"
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>--prefix</TT
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> option as other eCos host-side
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software, especially the I/O auxiliary provided by the architectural
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synthetic target HAL package, otherwise the I/O auxiliary will be
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unable to locate the watchdog support.
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</P
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="SYNTH-WATCHDOG-TARGET-CONFIG"
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></A
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><H2
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>Target-side
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Configuration</H2
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><P
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>The watchdog device depends on the generic watchdog support,
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<TT
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CLASS="VARNAME"
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>CYGPKG_IO_WATCHDOG</TT
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>: if the generic support is
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absent then the watchdog device will be inactive. Some templates
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include this generic package by default, but not all. If the
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configuration does not include the generic package then it can be
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added using the eCos configuration tools, for example:
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</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>$ ecosconfig add CYGPKG_IO_WATCHDOG</PRE
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></TD
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></TR
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></TABLE
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><P
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>By default the configuration will use the hardware-specific support,
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i.e. this package. However the generic watchdog package contains an
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alternative implementation using the kernel alarm facility, and that
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implementation can be selected if desired. However usually it will be
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better to rely on an external watchdog facility as provided by the I/O
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auxiliary and the <TT
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CLASS="FILENAME"
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>watchdog.tcl</TT
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> script: if there
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are serious problems within the application, for example memory
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corruption, then an internal software-only implementation will not be
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reliable.
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</P
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><P
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>The watchdog resolution is currently fixed to one second: if the
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device does not receive a reset signal at least once a second then
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the watchdog will trigger and the eCos application will be terminated
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with a <TT
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CLASS="LITERAL"
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>SIGPWR</TT
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> signal. The current implementation
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does not allow this resolution to be changed.
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</P
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><P
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>On some targets the watchdog device does not perform a hard reset.
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Instead the device works more or less via the interrupt subsystem,
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allowing application code to install action routines that will be
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called when the watchdog triggers. The synthetic target watchdog
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support effectively does perform a hard reset, by sending a
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<TT
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CLASS="LITERAL"
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>SIGPWR</TT
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> signal to the eCos application, and there is
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no support for action routines.
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</P
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><P
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>The synthetic target watchdog package provides some configuration
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options for manipulating the compiler flags used for building the
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target-side code. That code is fairly simple, so for nearly all
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applications the default flags will suffice.
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</P
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><P
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>It should be noted that the watchdog device is subject to selective
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linking. Unless some code explicitly references the device, for
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example by calling the start and reset functions, the watchdog support
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will not appear in the final executable. This is desirable because a
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watchdog device has no effect until started.
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</P
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="SYNTH-WATCHDOG-WALLCLOCK-ELAPSED"
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></A
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><H2
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>Wallclock versus Elapsed Time</H2
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><P
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>On real hardware the watchdog device uses wallclock time: if the
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device does not receive a reset signal within a set period of time
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then the watchdog will trigger. When developing for the synthetic
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target this is not always appropriate. There may be other processes
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running, using up some or most of the cpu time. For example, the
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application may be written such that it will issue a reset after some
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calculations which are known to complete within half a second, well
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within the one-second resolution of the watchdog device. However if
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other Linux processes are running then the synthetic target
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application may get timesliced, and half a second of computation may
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take several seconds of wallclock time.
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</P
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><P
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>Another problem with using wallclock time is that it interferes with
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debugging: if the application hits a breakpoint then it is unlikely
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that the user will manage to restart it in less than a second, and the
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watchdog will not get reset in time.
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</P
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><P
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>To avoid these problems the synthetic target watchdog normally uses
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consumed cpu time rather than wallclock time. If the application is
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timesliced or if it is halted inside gdb then it does not consume any
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cpu time. The application actually has to spend a whole second's worth
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of cpu cycles without issuing a reset before the watchdog triggers.
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</P
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><P
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>However using consumed cpu time is not a perfect solution either. If
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the application makes blocking system calls then it is not using cpu
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time. Interaction with the I/O auxiliary involves system calls, but
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these should take only a short amount of time so their effects can be
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ignored. If the application makes direct system calls such as
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<TT
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CLASS="FUNCTION"
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>cyg_hal_sys_read</TT
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> then the system behaviour
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becomes undefined. In addition by default the idle thread will make
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blocking <TT
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CLASS="FUNCTION"
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>select</TT
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> system calls, effectively waiting
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until an interrupt occurs. If an application spends much of its time
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idle then the watchdog device may take much longer to trigger than
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expected. It may be desirable to enable the synthetic target HAL
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configuration option <TT
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CLASS="VARNAME"
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>CYGIMP_HAL_IDLE_THREAD_SPIN</TT
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>,
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causing the idle thread to spin rather than block, at the cost of
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wasted cpu cycles.
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</P
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><P
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>The default is to use consumed cpu time, but this can be changed in
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the target definition file:
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</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>synth_device watchdog {
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use wallclock_time
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…
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}</PRE
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></TD
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></TR
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></TABLE
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="SYNTH-WATCHDOG-GUI"
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| 330 |
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></A
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| 331 |
|
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><H2
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| 332 |
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>User Interface</H2
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| 333 |
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><P
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| 334 |
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>When the synthetic target is run in graphical mode the watchdog device
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extends the user interface in two ways. The <SPAN
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CLASS="GUIMENU"
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>Help</SPAN
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>
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menu is extended with an entry for the watchdog-specific
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documentation. There is also a graphical display of the current state
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of the watchdog. Initially the watchdog is asleep:
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</P
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><DIV
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CLASS="INFORMALFIGURE"
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><A
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NAME="AEN60"><P
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></P
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><DIV
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CLASS="MEDIAOBJECT"
|
| 350 |
|
|
><P
|
| 351 |
|
|
><IMG
|
| 352 |
|
|
SRC="asleep.gif"
|
| 353 |
|
|
ALIGN="CENTER"></P
|
| 354 |
|
|
></DIV
|
| 355 |
|
|
><P
|
| 356 |
|
|
></P
|
| 357 |
|
|
></DIV
|
| 358 |
|
|
><P
|
| 359 |
|
|
>When application code starts the device the watchdog will begin to
|
| 360 |
|
|
keep an eye on things (or occasionally both eyes).
|
| 361 |
|
|
</P
|
| 362 |
|
|
><DIV
|
| 363 |
|
|
CLASS="INFORMALFIGURE"
|
| 364 |
|
|
><A
|
| 365 |
|
|
NAME="AEN65"><P
|
| 366 |
|
|
></P
|
| 367 |
|
|
><DIV
|
| 368 |
|
|
CLASS="MEDIAOBJECT"
|
| 369 |
|
|
><P
|
| 370 |
|
|
><IMG
|
| 371 |
|
|
SRC="awake.gif"
|
| 372 |
|
|
ALIGN="CENTER"></P
|
| 373 |
|
|
></DIV
|
| 374 |
|
|
><P
|
| 375 |
|
|
></P
|
| 376 |
|
|
></DIV
|
| 377 |
|
|
><P
|
| 378 |
|
|
>If the watchdog triggers the display will change again, and optionally
|
| 379 |
|
|
the user can receive an audible alert. The location of the watchdog
|
| 380 |
|
|
display within the I/O auxiliary's window can be controlled via
|
| 381 |
|
|
a <B
|
| 382 |
|
|
CLASS="COMMAND"
|
| 383 |
|
|
>watchdog_pack</B
|
| 384 |
|
|
> entry in the target definition
|
| 385 |
|
|
file. For example the following can be used to put the watchdog
|
| 386 |
|
|
display to the right of the central text window:
|
| 387 |
|
|
</P
|
| 388 |
|
|
><TABLE
|
| 389 |
|
|
BORDER="5"
|
| 390 |
|
|
BGCOLOR="#E0E0F0"
|
| 391 |
|
|
WIDTH="70%"
|
| 392 |
|
|
><TR
|
| 393 |
|
|
><TD
|
| 394 |
|
|
><PRE
|
| 395 |
|
|
CLASS="PROGRAMLISTING"
|
| 396 |
|
|
>synth_device watchdog {
|
| 397 |
|
|
watchdog_pack -in .main.e -side top
|
| 398 |
|
|
…
|
| 399 |
|
|
}</PRE
|
| 400 |
|
|
></TD
|
| 401 |
|
|
></TR
|
| 402 |
|
|
></TABLE
|
| 403 |
|
|
><P
|
| 404 |
|
|
>The user interface section of the generic synthetic target HAL
|
| 405 |
|
|
documentation can be consulted for more information on window packing.
|
| 406 |
|
|
</P
|
| 407 |
|
|
><P
|
| 408 |
|
|
>By default the watchdog support will not generate an audible alert
|
| 409 |
|
|
when the watchdog triggers, to avoid annoying colleagues. Sound can be
|
| 410 |
|
|
enabled in the target definition file, and two suitable files
|
| 411 |
|
|
<TT
|
| 412 |
|
|
CLASS="FILENAME"
|
| 413 |
|
|
>sound1.au</TT
|
| 414 |
|
|
> and <TT
|
| 415 |
|
|
CLASS="FILENAME"
|
| 416 |
|
|
>sound2.au</TT
|
| 417 |
|
|
> are
|
| 418 |
|
|
supplied as standard:
|
| 419 |
|
|
</P
|
| 420 |
|
|
><TABLE
|
| 421 |
|
|
BORDER="5"
|
| 422 |
|
|
BGCOLOR="#E0E0F0"
|
| 423 |
|
|
WIDTH="70%"
|
| 424 |
|
|
><TR
|
| 425 |
|
|
><TD
|
| 426 |
|
|
><PRE
|
| 427 |
|
|
CLASS="PROGRAMLISTING"
|
| 428 |
|
|
>synth_device watchdog {
|
| 429 |
|
|
sound sound1.au
|
| 430 |
|
|
…
|
| 431 |
|
|
}</PRE
|
| 432 |
|
|
></TD
|
| 433 |
|
|
></TR
|
| 434 |
|
|
></TABLE
|
| 435 |
|
|
><P
|
| 436 |
|
|
>An absolute path can be specified if desired:
|
| 437 |
|
|
</P
|
| 438 |
|
|
><TABLE
|
| 439 |
|
|
BORDER="5"
|
| 440 |
|
|
BGCOLOR="#E0E0F0"
|
| 441 |
|
|
WIDTH="70%"
|
| 442 |
|
|
><TR
|
| 443 |
|
|
><TD
|
| 444 |
|
|
><PRE
|
| 445 |
|
|
CLASS="PROGRAMLISTING"
|
| 446 |
|
|
>synth_device watchdog {
|
| 447 |
|
|
sound /usr/share/emacs/site-lisp/emacspeak/sounds/default-8k/alarm.au
|
| 448 |
|
|
…
|
| 449 |
|
|
}</PRE
|
| 450 |
|
|
></TD
|
| 451 |
|
|
></TR
|
| 452 |
|
|
></TABLE
|
| 453 |
|
|
><P
|
| 454 |
|
|
>Sound facilities are not built into the I/O auxiliary itself, instead
|
| 455 |
|
|
an external program is used. The default player is
|
| 456 |
|
|
<B
|
| 457 |
|
|
CLASS="COMMAND"
|
| 458 |
|
|
>play</B
|
| 459 |
|
|
>, a front-end to the
|
| 460 |
|
|
<SPAN
|
| 461 |
|
|
CLASS="APPLICATION"
|
| 462 |
|
|
>sox</SPAN
|
| 463 |
|
|
> application shipped with some Linux
|
| 464 |
|
|
distributions. If another player should be used then this can be
|
| 465 |
|
|
specified in the target definition file:
|
| 466 |
|
|
</P
|
| 467 |
|
|
><TABLE
|
| 468 |
|
|
BORDER="5"
|
| 469 |
|
|
BGCOLOR="#E0E0F0"
|
| 470 |
|
|
WIDTH="70%"
|
| 471 |
|
|
><TR
|
| 472 |
|
|
><TD
|
| 473 |
|
|
><PRE
|
| 474 |
|
|
CLASS="PROGRAMLISTING"
|
| 475 |
|
|
>synth_device watchdog {
|
| 476 |
|
|
…
|
| 477 |
|
|
sound_player my_sound_player</PRE
|
| 478 |
|
|
></TD
|
| 479 |
|
|
></TR
|
| 480 |
|
|
></TABLE
|
| 481 |
|
|
><P
|
| 482 |
|
|
>The specified program will be run in the background with a single
|
| 483 |
|
|
argument, the sound file.
|
| 484 |
|
|
</P
|
| 485 |
|
|
></DIV
|
| 486 |
|
|
><DIV
|
| 487 |
|
|
CLASS="REFSECT1"
|
| 488 |
|
|
><A
|
| 489 |
|
|
NAME="DEVS-WATCHDOG-SYNTH-ARGS"
|
| 490 |
|
|
></A
|
| 491 |
|
|
><H2
|
| 492 |
|
|
>Command Line Arguments</H2
|
| 493 |
|
|
><P
|
| 494 |
|
|
>The watchdog support does not use any command line arguments. All
|
| 495 |
|
|
configuration is handled through the target definition file.
|
| 496 |
|
|
</P
|
| 497 |
|
|
></DIV
|
| 498 |
|
|
><DIV
|
| 499 |
|
|
CLASS="REFSECT1"
|
| 500 |
|
|
><A
|
| 501 |
|
|
NAME="DEVS-WATCHDOG-SYNTH-HOOKS"
|
| 502 |
|
|
></A
|
| 503 |
|
|
><H2
|
| 504 |
|
|
>Hooks</H2
|
| 505 |
|
|
><P
|
| 506 |
|
|
>The watchdog support does not provide any hooks for use by other
|
| 507 |
|
|
scripts. There is rarely any need for customizing the system's
|
| 508 |
|
|
behaviour when a watchdog triggers because those should be rare
|
| 509 |
|
|
events, even during application development.
|
| 510 |
|
|
</P
|
| 511 |
|
|
></DIV
|
| 512 |
|
|
><DIV
|
| 513 |
|
|
CLASS="REFSECT1"
|
| 514 |
|
|
><A
|
| 515 |
|
|
NAME="DEVS-WATCHDOG-SYNTH-TCL"
|
| 516 |
|
|
></A
|
| 517 |
|
|
><H2
|
| 518 |
|
|
>Additional Tcl Procedures</H2
|
| 519 |
|
|
><P
|
| 520 |
|
|
>The watchdog support does not provide any additional Tcl procedures or
|
| 521 |
|
|
variables for use by other scripts.
|
| 522 |
|
|
</P
|
| 523 |
|
|
></DIV
|
| 524 |
|
|
></BODY
|
| 525 |
|
|
></HTML
|
| 526 |
|
|
>
|
