Experimental Physics and
Industrial Control System

John Dobbins <[email protected]> · Sat, 04 Feb 2006 20:30:31 -0500

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System