Experimental Physics and
Industrial Control System

<[email protected]> · Fri, 27 Jun 2014 17:01:26 +0000

All,

What is the correct thing to do when a bad link name is encountered at initialisation? 

We recently had a problem when an string parameter was badly named in the OUT link of  stringoutRecord of an areaDetector device. This printed an error message at start up (which no-one saw) but didn't disable the record and subsequent writes to the record (by autosave/restore) trashed the first parameter in the device (which was also a string). I don't think this is the right thing to do.

The rough call chain at the time of the problem is that iocInit initialises the record by calling:

prec->rset->init_record (i.e. init_record in stringoutRecord.c)
  prec->dset->init_record (i.e. initSoWrite in devAsynOctet.c)
    initDrvUser in devAsynOctet.c
       ... 
       asynPortDriver::drvUserCreate in asynPortDriver.cpp

The bottom routine prints an error message because it can't find the parameter and returns bad status but doesn't change pasynUser->reason. 

Then initDrvUser also printed an error, but couldn't do anything more since it is a void function. Hence the record didn't know there was a problem and believed that initialisation had succeeded.

If it did return an error it could propagate it up to the initSoWrite function which has access to the record structure and so could change the value of fields or return an error to record support. If record support gets an error it returns it to iocInit, but otherwise ignores it. iocInit then ignores any bad status.

The options are:
 - set the reason to -1 and check for it in asynPortDriver so any subsequent write fails.
 - change initDrvUser to return a status and disable the record somehow (or set it to Soft Channel) in device support, record support or iocInit.

In similar circumstances devAsynInt32 tries to disable the record by setting pact to 1 and returning a bad status - is this the right thing to do? I looked at various other device drivers and consistency wasn't a feature. Some called recGblRecordError, but this only prints a message, doesn't disable the record.

I know that consistency in device support isn't one of EPICS's features, but if we could decide on a reasonable approach I would be happy to make asyn adhere to it...

Cheers,

Nick Rees
Principal Software Engineer           Phone: +44 (0)1235-778430
Diamond Light Source                  Fax:   +44 (0)1235-446713

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System