Experimental Physics and
Industrial Control System

Nicholas DiMonte <[email protected]> · Fri, 25 Jan 2002 13:22:57 -0600

I had a similar problems in the past. I use the "pvConnected" command
to verify a connection before reading any pv from another IOC.

Nick

Advance Photon Source
Argonne, Il 60439 USA
Phone: 630-252-8856
Fax:     630-252-6123
Email:  [email protected]

Andy Foster wrote:

> I have recently experienced something strange with the
> sequencer. This is EPICS 3.13.4, sequencer Version 1.9.2.Beta12.
>
> What happened was this. In IOC1, a sequence program was
> looping with a 1 second delay. Each time through the loop,
> it called pvGet on a record field which was an array of
> 6 doubles. This record was in IOC2.
>
> With IOC1 and IOC2 running everything was fine.
> However, when IOC2 was rebooted, I started getting garbage values in
> the array elements in IOC1 as a result of the pvGet. Numbers the
> size of 10**271 appeared after the disconnect event.
> This caused my application in IOC1 to crash with
> "Floating point overflow".
>
> I traced this down to what I think maybe a bug in the
> sequencer. When a pvGet completes, there is an unconditional
> copy of the data in the Channel Access structure to the user's
> variable. This is a "bcopy" in "seq_ca.c".
>
> What seemed to be missing was a check on "args.status" for
> ECA_NORMAL before doing this copy. "args" are returned from
> the sequencer event handler routine "seq_event_handler".
> Putting in this check, solved the problem.
>
> There is a question over what to do with the users variable
> (memory space) if the CA status is not ECA_NORMAL.
> I chose to set it to 0. The
> alternative, I guess, would be to leave the value as it was
> before the pvGet failure.
>
> I looked at seq-2.0.1, and saw that it has lots of changes
> made by William Lupton (to support 3.14 and some bug fixes).
> But, looking at the code, it wasn't obvious to me that this
> particular problem had been addressed.
>
> Is there a version of the sequencer available which just has
> the bug fixes and so will run with 3.13.4? Then, I could
> try that version out and, if necessary, my fix could be
> added to this.
>
> Cheers,
>
> Andy
>
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System