Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Mon, 20 Dec 2021 21:15:57 -0800

On 12/20/21 4:22 PM, Wang, Andrew via Tech-talk wrote:
> All,
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> 
> Quick question.
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> 
> Suppose I have two analog input records called “A” and “B” on which I would like to do caput. If I have a bash script containing the following code:
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> caput A 100
> 
> caput B 200
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> Will that give sufficient time for caput to respond? Or should there ideally be a “delay” between each caput. The reason why I ask is because within the sequencer, we do something similar, but with pvPut, and sometimes we see that “B” does not get updated with a new value.

By default, ordering w/ CA (and PVA) is not strict.  As you have found
in the situation you describe, it is possible for the effects of B to
precede A.  With CA this can be made stricter with the ca_put_callback
operation.

> caput -c A 100
> caput -c B 200

Adding '-c' will cause caput to wait for the server/IOC to confirm that
the PUT has been completely processed before exiting.  (note also '-w'
for a timeout on this wait)

It's been awhile since I did this in the sequencer.  As I read it, passing
ASYNC or SYNC to pvPut() has the same effect as '-c'.  The difference
between these two modifiers is in how your sequencer program will need to
be adjusted to wait for the PUT operation(s) to complete.

cf. pvPut(), pvPutComplete(), pvPutCancel(), and the pvArray*() variants.

https://www-csr.bessy.de/control/SoftDist/sequencer/Reference.html?highlight=pvput#pvput

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System