Re: StreamDevice and AMSG field

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 5/20/25 01:00, Zimoch Dirk via Tech-talk wrote:
> Hi Dennis
>
> Yes, that field is new and not yet supported by StreamDevice.
> The idea of that field is to store clear text error messages together with the alarm status/severity for easier debugging. StreamDevice could use it to store messages like "Parse Error", "Connection lost", "Reply timeout" etc.
> The field is not modifiable by dbPutField and thus neither by caput nor by redirection from a StreamDevice protocol.
> As storing something into AMSG uses a totally different method, it would be difficult to make it writable by redirections.

AMSG is intended to provide context for STAT and SEVR, about the active record alarm.

As device support should not write directly to STAT and SEVR, neither should it write AMSG.

The interface for writing to all three fields is the "recGblSetSevrMsg()" function,
which is an extension of "recGblSetSevr()".  These functions implement the Maximize
Severity algorithm to ensure that all three fields are consistent.

> DBCORE_API int recGblSetSevrMsg(void *precord, epicsEnum16 new_stat,
>                                 epicsEnum16 new_sevr,
>                                 EPICS_PRINTF_FMT(const char *msg), ...) EPICS_PRINTF_STYLE(4,5);

So Stream could be updated to call recGblSetSevrMsg() here:

> $ git grep recGblSetSevr
> src/StreamEpics.cc:        (void) recGblSetSevr(record, UDF_ALARM, INVALID_ALARM);
> src/StreamEpics.cc:            (void) recGblSetSevr(record, status, INVALID_ALARM);
> src/StreamEpics.cc:        (void) recGblSetSevr(record, UDF_ALARM, INVALID_ALARM);
> src/StreamEpics.cc:        (void) recGblSetSevr(record, status ? status : UDF_ALARM, INVALID_ALARM);
> src/StreamEpics.cc:                (void) recGblSetSevr(pdbaddr->precord,
> src/devmbboStream.c:        recGblSetSevr(record, STATE_ALARM, mbbo->unsv);
> src/devmbboStream.c:        recGblSetSevr(record, STATE_ALARM, (&(mbbo->zrsv))[mbbo->val]);
> src/devmbboStream.c:        if (!recGblSetSevr(record, COS_ALARM, mbbo->cosv)) mbbo->lalm = mbbo->val;

There is a feature test macro also defined in recGbl.h

> /** Feature test macro for alarm message (AMSG) field and support
>  *
>  * Covers addition of dbCommon::amsg, recGblSetSevrMsg(), lset::getAlarmMsg()
>  *
>  * @since 7.0.6
>  */
> #define HAS_ALARM_MESSAGE 1




> Dirk
>
> > -----Original Message-----
> > From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Neidherr, Dennis
> > Dr. via Tech-talk
> > Sent: Dienstag, 20. Mai 2025 08:57
> > To: tech-talk at aps.anl.gov
> > Subject: StreamDevice and AMSG field
> >
> > Dear all,
> >
> > and again a small question:
> > According to the documentation there is a (new?) field called AMSG to store
> > alarm (or error) messages. Is this somehow also useable with StreamDevice?
> > Because this field is marked as "non-writable", I can not simply redirect errors
> > into it like I tried here:
> >
> > setAmplitude0 {
> >      out ":SOUR1:VOLT %f;:SYST:ERR?";
> > 	in "+%(myAgilent:ErrorCode)i,\"No error\"";
> > 	# @mismatch { in
> > "%(myAgilent:ErrorCode)i,\"%(myAgilent:ErrorMsg)#s\"" }
> > 	@mismatch { in "%(myAgilent:ErrorCode)i,\"%(AMSG)#s\"" }
> > 	@writetimeout { disconnect; }
> > 	@readtimeout { disconnect; }
> > 	@replyTimeout { disconnect; }
> > }
> >
> > I can certainly use another record to store errors but with the AMSG-field this
> > would be a more elegant way. So, is there some workaround or have I maybe
> > missed something?
> >
> > Thanks and
> > Greetings Dennis