ASYN/devGPIB/GPIBCVTIO problem

[John Dobbins <jad@lepp.cornell.edu>]

A follow up note:

I changed dfanoutRecord DOL to be "aiRecord.VAL NPP" and then used a seq record 
to first process aiRecord and then after a delay process dfanoutRecord.

This fixes the bad behavior which is consistent with the theory that dfanout was 
grabbing aiRecord.VAL too soon.

Also note that if I replace dfanout with an ao, DTYP = "Soft Channel" I see the 
same behavior, so this problem is not specific to dfanout.

John


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Dear All,

I am confused about what is happening with an Analog In record connected to an
ASYN device. In particular this is a devGPIB device with a command of type
GPIBCVTIO.

I have created the custom convert routine for this devGPIB GPIBCVTIO command and
it appears to work, i.e. I have connected it to an Analog In record and if from
the EPICS command line I force the record to process (dbpf aiRecord.PROC 1) and
then examine the record's value (dbpr aiRecord) it has correctly retrieved the
value from hardware.

However, I next did the following:

I added a dfanout record and an Analog Out record. All three records are
passive. I set the DOL of the dfanout record to be the "aiRecord.VAL PP" and
OUTA of the dfanout record to be the "aoRecord.VAL PP".

      aiRecord -> dfanoutRecord -> aoRecord

I see this behavior when I make dfanoutRecord process:

1) aiRecord processes
3) ao record processes writing the stale value, i.e. the value the aiRecord had
before it processed

Note, from ASYN diagnostic output I see #1 happen and then #3 happen.

I infer that in between these the following happened

2) dfanoutRecord retrieved stale data from aiRecord and passed it to aoRecord

So the question is why is the dfanout record retrieving the stale value? It
seems it must be that the value is retrieved before the aiRecord is actually
done processing.

The last lines of my convert routine are:

       precord->val = floatData;
       precord->udf = 0;

      return 0;
  }

After which the code in devGPIB is responsible for setting PACT = 0.

Have I gone wrong somewhere? Any advice appreciated.

info: EPICS 3.14.7, ASYN 4.2.1, Linux IOC


Thanks,

John Dobbins
Cornell University
Lab for Elementary Particle Physics
Ithaca, NY