Experimental Physics and
Industrial Control System

Torsten Bögershausen via Core-talk <core-talk at aps.anl.gov> · Tue, 30 Jun 2020 18:14:10 +0200

On 30/06/20 17:55, Johnson, Andrew N. wrote:

Hi Torsten,

On Jun 30, 2020, at 3:09 AM, Torsten Bögershausen via Core-talk

<core-talk at aps.anl.gov <mailto:core-talk at aps.anl.gov>> wrote:

I have a problem with dbLinkIsConstant(), it seems.

If I run the motor module with this code:

#if LT_EPICSBASE(7,0,0,0)
#define dbLinkIsConstant(lnk) ((lnk)->type == CONSTANT)
#else
#include "dbLink.h"
#endif

And later

   if (dbLinkIsConstant(&pmr->dol))
   {
       pmr->udf = FALSE;

       Debug(pmr,3, "init_record %s\n", "dbLinkIsConstant=true set

UDF=FALSE");

       recGblInitConstantLink(&pmr->dol, DBF_DOUBLE, &pmr->val);
   }

I get this log message:

[motorRecord.cc:906 <http://motorrecord.cc:906>  IOC:m1] init_record

dbLinkIsConstant=true set UDF=FALSE

However, the .DOL field is empty.
Is this the expected behavior ?

Yes, an empty or unpopulated link field has always been represented with

type==CONSTANT which is a macro with value 0 so this is also the default

if the link field is not set at all. In 3.16.1 I introduced extensible

links and the dbLinkIsConstant() routine to Base because extensible

links can also provide constant values, and they don’t have type==CONSTANT.

Note that recGblInitConstantLink() has always returned TRUE if the link

is a constant and provided a value (else FALSE), so there is no actual

need for the conditional around it – that was merely an optimization for

earlier versions of Base but is no longer helpful. My suggested

replacement for the code above is to not call dbLinkIsConstant() at all,

just do this instead:

   if (recGblInitConstantLink(&pmr->dol, DBF_DOUBLE, &pmr->val))
   {
       pmr->udf = FALSE;

       Debug(pmr,3, "init_record %s\n", "recGblInitConstantLink set

UDF=FALSE");

   }

That should be backwards compatible with older Base versions, and I

believe all of the record types  have now had that modification done

already. This was documented in the Release Notes for version 3.16.1

<https://epics.anl.gov/base/R3-16/1-docs/RELEASE_NOTES.html>, look for

the section titled “Support Routine Modifications for Extensible Link

Types”.

HTH,

- Andrew

--
Complexity comes for free, simplicity you have to work for.

Thanks Andrew for the good explanation
I (now) realized that I had mis-used the .UDF field to keep track
if there was ever a communication to the controller, or if it is still
"offline". The .UDF seemed good for this purpose, but it isn't.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System