Re: Embedded EPICS IOC

[Andrew Johnson <anj@aps.anl.gov>]

Hi David,

David DeBonis wrote:
> We are working on an embedded EPICS IOC deployment but are running into 
> some confusion on what is necessary to build to our target architecture 
> which is ARM running a linux kernel 2.6.x.  We have our 
> own cross-compilers that we would like to use and build with but we seem 
> to be running into issue with some post-build executables that need to 
> be run on the target.
>  
> Can someone clarify what EPICS binaries are necessary to be deployed to 
> the target to run as a "Soft IOC" standalone?  Also, can we 
> cross-compile all we need on our host system yet run fully standalone on 
> the target?

You've probably come across the issue with the CA Repeater.  All IOCs 
contain the CA Client library, and when it starts up the client library 
looks for a running CA Repeater on the localhost network interface.  If 
it doesn't find one, it will fork and attempt to exec the caRepeater binary.

In the case of a purely embedded IOC you have two choices about how to 
solve this issue and prevent the warning message that appears if the 
exec is unsuccessful.  The simplest solution is to include the 
caRepeater on your target disk partition and arrange for it to be run 
before the IOC starts.  It should never exit even if the IOC does, so it 
should never need restarting.  With this solution you will need to 
include the caRepeater executable on the target as well as the ioc itself.

The alternative solution is to explicitly start the repeater as a 
separate thread within the IOC's main() program.  This may use slightly 
fewer resources than when running it in a separate process (not least 
because you don't need the separate caRepeater executable), but it is a 
little more complicated to set up as it requires adding some lines to 
main(), and it is not guaranteed to work unchanged on different versions 
of EPICS Base since the caRepeaterThread() routine is not an official 
API.  The code you would need is as follows:

    #include "epicsThread.h"
    extern "C" void caRepeaterThread (void *);

    epicsThreadCreate("CAC-repeater", epicsThreadPriorityLow,
        epicsThreadGetStackSize(epicsThreadStackMedium),
        caRepeaterThread, 0);

That epicsThreadCreate() call should appear at the top of the main() 
definition in your IOC's xxxApp/src/xxxMain.cpp file.

You should be able to do what you want using a linux-arm cross-compiler 
to generate a fully stand-alone ioc executable (and caRepeater if you 
chose the first option above).  You might also want to experiment with 
statically linking against the EPICS libraries, for which there are 
controls in the EPICS build system to turn off building shared libraries 
(make sure you remove the lib*.so files from your lib/linux-arm 
directories if you do that).  If you stick with the shared libraries, 
you'll need to copy them all to the target as well as the executables, 
and be aware of the issues of the runtime search path to find them all.

HTH,

- Andrew
--
When a distinguished but elderly scientist states that something is
possible, he is almost certainly right.  When he states that something
is impossible, he is very probably wrong.  -- Arthur C. Clarke