Experimental Physics and
Industrial Control System

Rolf Keitel <[email protected]> · Fri, 14 Jun 2013 07:24:16 -0700

I ran into some  behaviour of the analog output record which surprised me:

I have several ao records, all DTYP="Soft Channel", which - when

processed - are meant to send different constant values each to a target

record.

I am setting DOL to the desired constant value and OMSL=closed_loop and

everything seems to work as desired.

When I do a caput to one of these ao records, however, the record

outputs from this moment the value received from the caput and ignores

the DOL value.

This seems counter-intuitive to me. I had expected that in closed_loop

mode, the VAL field would be *always* obtained from the DOL link.

The record processing routine shows that this is the programmed

behaviour (during record init the VAL field has been loaded from the

constant link):

    ...
    /* fetch value and convert*/
    if (prec->pact == FALSE) {
                if ((prec->dol.type != CONSTANT)
                && (prec->omsl == menuOmslclosed_loop)) {
                    status = fetch_value(prec, &value);
                }
                else {
                    value = prec->val;
                }
        if(!status) convert(prec, value);
        prec->udf = isnan(prec->val);
    }
    ...

The recordreference manual (3.14) does not say anything about the

behaviour of a constant link:

"... If closed_loop is specified, the VAL field's value is obtained from

the address specified in the desired output location field (DOL), which

can be either a database link or a channel access link. ..."

Does anyone remember what the rationale is for treating a constant link

differently from a db or ca link?

- rolf -

--
+-------------------------------------------------------+
| Rolf Keitel, Ph.D.                Tel: (604) 222-7453 |
| TRIUMF                                                |
| Vancouver, B.C., Canada                               |
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System