Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Wed, 04 Mar 1998 09:24:30 -0600

Noboru Yamamoto wrote:
> 
> Dear Colleague,
> 
>  One of my colleague try to get output value of AO record from the record
> on another IOC. So he put channel name in DOL field. After initializing
> IOC, dbpr command shows that DOL has CA_LINK.
> However value which this AO record got is jut garbage.
> After looking at the codes, aoRecord.c and aiRecord.c and devAiSoft.c,
> I modified one line of code in aoRecord.c. With this modification,
> AO record get correct number from CA_LINK.
> I'm not quite sure if it has another side effect. Honestly speaking,
> I don't understand why original code get the garbage and why the modified
> version does get the correct number.
> 
> Anyway, here is a original code in aoRecord.c.
> 
> ===== extracted from aoRecord.c ======================================
> static long process(pao)
>         struct aoRecord     *pao;
> {
>         struct aodset   *pdset = (struct aodset *)(pao->dset);
>         long             status=0;
>         unsigned char    pact=pao->pact;
>         double          value;
> 
>         if ((pdset==NULL) || (pdset->write_ao==NULL)) {
>                 pao->pact=TRUE;
>                 recGblRecordError(S_dev_missingSup,(void *)pao,"write_ao");
>                 return(S_dev_missingSup);
>         }
> 
>         /* fetch value and convert*/
>         if (pao->pact == FALSE) {
>                 if ((pao->dol.type != CONSTANT) &&
>                     (pao->omsl == CLOSED_LOOP)) {
>                    fetch_value(pao, &value);
>                 }
>                 else {
>                    value = pao->val;
>                 }
>                 convert(pao, &value);
>         }
> ...
> =========================================================================

I looked a little closer and I think the problem is that fetch_value
does not change value if dbGetLink reports an error. Since value is not
initialized it is just garbage in this case. This will happen whenever
the CA link has a problem.

Noboru,

Is this what happened?

If this is true then the change should be:

        /* fetch value and convert*/
        if (pao->pact == FALSE) {
                if ((pao->dol.type != CONSTANT) &&
                    (pao->omsl == CLOSED_LOOP)) {

                   status = fetch_value(pao, &value);
                }
                else {
                   value = pao->val;
                }
                if(!status) convert(pao, value);
        }

And fetch_value modified to return a status value.
I will change it for the next release of epics.

Marty Kraimer

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System