Re: devSnmp, device replying with a string containing units

[Marco Filho via Tech-talk <tech-talk at aps.anl.gov>]

Hi, Andrea

According to the documentation I found here: https://groups.frib.msu.edu/controls/files/devSnmp.html in the topic set_type you need to set the type of the variable that you are getting. 'i' for integer, 'f' for floating point, 's' for string.

An example record that I got from one IOC:

record(ai, "$(P)$(R)InputVoltage$(CH)-R") {
    field(DESC, "Present input voltage in channel $(CH)")
    field(EGU,  "RMS V (AC)")
    field(DTYP, "Snmp")
    field(SCAN, ".5 second")
    field(PREC, "1")
    field(INP,  "@$(HOST) $(COMMUNITY) UPS-MIB::upsInputVoltage.$(CH) INTEGER: 100 i")
}

Maybe that helps? I'm not sure.

Cheers,

Marco

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Andrea Celentano via Tech-talk <tech-talk at aps.anl.gov>
Sent: 06 March 2025 15:21:26
To: tech-talk at aps.anl.gov
Subject: devSnmp, device replying with a string containing units

 

Dear colleagues, 

I have a device that can be programmed using SNMP (Wiener MPOD crate). 

A typical reply to the command:

snmpget  -v 2c -m +WIENER-CRATE-MIB -c guru 10.152.72.10 outputVoltage.u0

Looks as:

WIENER-CRATE-MIB::outputVoltage.u0 = Opaque: Float: 0.000000 A

Where, as you see, the device replies with the number (0.0000) containing also units (A)

My record to read this is:

record(ai, “wienerCh0:v")

{

  field(DESC, “Voltage")

  field(DTYP, "Snmp")

  field(SCAN, "$(SCAN)")

  field(PREC, "3")

  field(EGU,  “V")

  field(INP,  “@10.152.72.10 guru WIENER-CRATE-MIB::outputVoltage.u0 Float: 100")

  field(ADEL, "1.0")  

}

If I execute my IOC, I get the error:

2025/03/06 15:00:49  devSnmp AI read error 'wienerCh0:v' : epicsScanDouble failed on '5.000000 V'

As if the IOC is not able to parse the “Volt” units. And indeed, the PV is not properly populated:

caget wienerCh0:v

wienerCh0:v            0

May I ask you if any of you also faced this issue? 

Thanks,

Andrea