Experimental Physics and
Industrial Control System

"Claus, Ric via Tech-talk" <tech-talk at aps.anl.gov> · Fri, 8 Dec 2023 23:56:58 +0000

Hello,

 I have written a PV server using P4P based on the lazycounter_server_cothread.py example in the P4P repository.  It uses NTScalars with the valueAlarm option set to True.  I am able to set valueAlarm fields through both the program and pvput commands and then see the results with pvget:

$ pvget -vv DAQ:NEH:tst:3:test_pv
DAQ:NEH:tst:3:test_pv epics:nt/NTScalar:1.0
   uint value 2
   alarm_t alarm
       int severity 0
       int status 0
       string message
   time_t timeStamp 2023-12-08 10:04:59.245
       long secondsPastEpoch 1702058699
       int nanoseconds 244999885
       int userTag 0
   structure valueAlarm
       boolean active true
       uint lowAlarmLimit 2
       uint lowWarningLimit 0
       uint highWarningLimit 0
       uint highAlarmLimit 4
       int lowAlarmSeverity 3
       int lowWarningSeverity 0
       int highWarningSeverity 0
       int highAlarmSeverity 3
       double hysteresis 0

However, I don’t see the alarm structure’s fields changing (although I’m not sure what to expect).  Where should the alarm evaluation occur?  

I found this comment in the Normative-Types-Specification page:

Code that checks for alarms should use code similar to the following:

followed by some C code showing how to do the alarm evaluation (without hysteresis) and raising.  Is it the intention that similar code should be in the application layer of my PV server, rather than in some common lower layer?  If so, how should this be done since I haven’t found the equivalent of some of these routines in P4P? 

Thank you for any guidance you can give me!

Ric Claus
SLAC/LCLS

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System