Re: question about pvmonitor behavior

[Alfio Rizzo via Tech-talk <tech-talk at aps.anl.gov>]

Hej Erico,

Your explanation is quite clear,

However I am confused why the .HIHI and other fields seems to be processed even if the PP attribute is missing.

I have checked a dfanout we use in some IOCs

record(dfanout, "$P$R:#FB_ProcHiValue") {
    field(DESC, "Set alarm limit value")
    field(DOL,  "$P$R:FB_ProcHiValue CP")
    field(OMSL, "closed_loop")
    field(OUTA, "$P$R:MeasValue.HIGH")
   
}

And according to the IOC owner, the value from $P$R:FB_ProcHiValue  is propagated to "$P$R:MeasValue.HIGH 

But again, if  it is instead field(OUTA, "$P$R:MeasValue.VAL") without the PP, as you wrote, the record is not processed as expected...

Anyway, since it is not harmful to put the PP attribute, we will update that kind of records adding it in the OUTA

Best

Alfio

______________________

 

Alfio Rizzo

PhD / Automation Section Leader / ICS HW&I Group

 

European Spallation Source ERIC

P.O. Box 176, SE-221 00 Lund, Sweden

Visiting address: Partikelgatan 2, 224 84 Lund

Mobile: +46 72 179 23 42

E-mail: alfio.rizzo at ess.eu

ess.eu

 

 

---

From: Érico Nogueira Rolim <erico.rolim at lnls.br>
Sent: Tuesday, March 17, 2026 2:33 PM
To: Alfio Rizzo <Alfio.Rizzo at ess.eu>; tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: question about pvmonitor behavior

 

Hi Alfio!

To make matters clear, the issue isn't pvmonitor vs camonitor, it's your OUT link. You should be using "myaipv PP" as the output link, to tell the record to process after it receives the write. Even if "pvget myaipv" showed the updated value, any other database or device support connections wouldn't have been updated (the same way the monitor command didn't receive any changes), since the record itself wasn't processed. Most of the time, OUT links should include PP. This is documented in [1].

IIRC writing into RVAL doesn't work correctly, but I'd welcome someone clearing that up.

HIHI is quite different from VAL, regarding the field definition:

    field(VAL,DBF_DOUBLE) {
        prompt("Current EGU Value")
        promptgroup("40 - Input")
        asl(ASL0)
        pp(TRUE)
    }

    field(HIHI,DBF_DOUBLE) {
        prompt("Hihi Alarm Limit")
        promptgroup("70 - Alarm")
        pp(TRUE)
        interest(1)
        prop(YES)       # get_alarm_double
    }

It's possible either interest(1) or prop(YES) cause HIHI changes to be propagated to monitors (probably prop(YES), given the get_alarm_double comment). However, from my quick testing, it doesn't actually cause the record to be processed, so you still need PP to cause processing.

[1] https:// docs.epics-controls.org/en/latest/appdevguide/lockScanProcess.html#process-passive

Cheers,

Érico

On 3/17/26 07:27, Alfio Rizzo via Tech-talk wrote:

Hej

I noticed that the pvmonitor of a record value does not update  when the .VAL is  changed from the  OUT field of another record,

E.g. Using this simple db

record(ai, "myaipv"){
   field(PINI, "YES")
   field(VAL, 100)
}

record(ao, "myaopv") {
   field(PINI, "YES")
   field(VAL, 30)
   field(OUT, "myaipv")  
}

If I do pvput myaovpv 1000, the myaipv.VAL is updated correctly (pvget myaipv gives back the updated value)

But this change is not shown in the pvmonitor  STDOUT

According to what I heard this is the intended behavior, but why apparently it applies only to  the .VAL field ?

I have tested the OUT with other fields like the alarm fields, or .RVAL , etc (i.e. OUT, "myaipv.HIHI") (OUT, "myaipv.RVAL")

Then if I do pvmonitor myaipv.HIHI for instance, everytime the myaopv value changes, 

The pvmonitor reacts as well showing the updated .HIHI field value

Can someone give some more explanation about ?

I am using EPICS 7.0.9/6.0.0

Thanks

Best

Alfio 

 

______________________

 

Alfio Rizzo

PhD / Automation Section Leader / ICS HW&I Group

 

European Spallation Source ERIC

P.O. Box 176, SE-221 00 Lund, Sweden

Visiting address: Partikelgatan 2, 224 84 Lund

Mobile: +46 72 179 23 42

E-mail: alfio.rizzo at ess.eu

ess.eu

 

 

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