Experimental Physics and
Industrial Control System

Eric Bjorklund <[email protected]> · Tue, 24 Apr 2001 18:37:08 -0600

I appear to have discovered a bug in longoutRecord.c under R3.13.4 which
probably dates back to R3.13.3, when the drvh & drvl fields were added.

The manifestation is that a longout record with OMSL in closed_loop and
a constant value in the DOL link, will end up with an arbitrary value
in VAL when the record is processed.

The culpret is in the following code from the "process" routine:

    if (!plongout->pact) {
            if (plongout->omsl == CLOSED_LOOP) {
                    status = dbGetLink(&(plongout->dol),DBR_LONG,
                            &value,0,0);
                    if (plongout->dol.type!=CONSTANT && RTN_SUCCESS(status))
                            plongout->udf=FALSE;
            }
            else {
                    value = plongout->val;
            }
            if (!status) convert(plongout,value);
     }

If dol.type is CONSTANT, dbGetLink does not fetch the link value, and so
the variable "value" is never initialized.

The fix, I've implemented for now is to initialize "value" in its declaration
at the begining of the process routine, i.e:

        long             value=plongout->val;

This restores the longout record to its previous behavior -- which is not
the same as, for example, an ao record with the similar setup since it
allows you to change the value by writing to the VAL field.  For that, however,
we'd probably have to add another field to longout (such as the ao's PVAL
field).

Eric Bjorklund
LANSCE-6 Controls
Los Alamos Neutron Scattering Center.
[email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System