Experimental Physics and
Industrial Control System

"J. Lewis Muir" <[email protected]> · Fri, 22 Nov 2013 11:39:15 -0600

On 11/22/13 11:16 AM, Andrew Johnson wrote:
> Hi Lewis,
>
> On 11/22/2013 10:53 AM, J. Lewis Muir wrote:
>> EPICS Base developers, it would be great if a write to the calcout
>> VAL field did trigger record processing.  But maybe there's a reason
>> why it doesn't?
>
> I didn't design that record type, but why would you want to be able
> to write a value to a field when that value is normally going to be
> immediately overwritten when the record processes?

Hi, Andrew.

My only reason is just from a PV "API" standpoint.  Lots of people leave
off the ".VAL" suffix from the PV name, so in this case, they wouldn't
be able to do that unless the VAL field was pp(TRUE).

> Note that the pp(TRUE) setting only applies when doing a put through
> CA, a database link can directly control whether processing happens or
> not.

Interesting.  Thanks for pointing that out; I didn't know that.

> In this particular case you're getting clever with the record so I do
> understand the request, but the ability to access the VAL field from a
> Calc expression is a lot newer than the calcout record. Note also that
> in an OCAL expression, VAL actually returns the last value from the
> OVAL field, not the VAL field, so setting OCAL to "1000 * VAL" would
> not do the scaling of the VAL field that Benoit wants it to do.

Right, that's what I said when I wrote, "So maybe you could write to
that [the OVAL field], and use the OCAL expression and set DOPT to 'Use
OCAL' and get the behavior you want by writing to OVAL instead of VAL
(albeit confusing)?"

Thanks,

Lewis

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System