Re: Disable alarm at IOC via PVAccess

[David Bracey via Tech-talk <tech-talk@aps.anl.gov>]

I’m afraid I’m not having any luck with that.  I should mention that I’m using softIocPVX and pvxget/pvxput to experiment with this.

 

I’m able to read the database fields STAT and SEVR with pvxget, but not allowed to set them with pvxput.

 

One puzzling thing is that the NT representation of the alarm info is alarm_t and valueAlarm_t, but the valueAlarm_t is constructed without an ‘enable’ field.  However, there are plenty of examples on the internet that show the full valueAlarm_t, including enable and hysteresis.

 

Can anyone tell me what governs the generation of the ‘enable’ field, and if it does exist, can I expect it to disable/enable the alarm?  Again, I’m looking for a general solution for any IOC (EPICS 7), so I don’t want to require custom code.

 

From: Tech-talk <tech-talk-bounces@aps.anl.gov> on behalf of Pierrick Hanlet via Tech-talk <tech-talk@aps.anl.gov>
Date: Wednesday, November 19, 2025 at 4:38 PM
To: tech-talk@aps.anl.gov <tech-talk@aps.anl.gov>
Subject: Re: Disable alarm at IOC via PVAccess

Hi Dave,
One can change the alarm severity to NO_ALARM.
Cheers,
Pierrick

On 11/19/25 16:27, David Bracey via Tech-talk wrote:

Is it possible to disable a PV’s alarm at the IOC, using PVAccess, on a “stock” IOC/PV?  (i.e. no custom code added)

 

I see that using channel access, one can disable the entire PV (via the DISV/DISA db fields) – however we are not using channel access.

 

Defining a simple DB record for a PV:

 

record(ai, "VAL1") {

    field(VAL, "1")

    field(SCAN, "1 second")

    field(HIHI, "2")

    field(LOLO, "0")

    field(HHSV, "MAJOR")

    field(LLSV, "MINOR")

}

One gets the following from pvxget:

 

VAL1

    value double = 1

    alarm.severity int32_t = 0

    alarm.status int32_t = 0

    alarm.message string = ""

    timeStamp.secondsPastEpoch int64_t = 1763589981

    timeStamp.nanoseconds int32_t = 529070863

    timeStamp.userTag int32_t = 0

    display.limitLow double = 0

    display.limitHigh double = 0

    display.description string = ""

    display.units string = ""

    display.precision int32_t = 0

    display.form.index int32_t = 0

    display.form.choices string[] = {7}["Default", "String", "Binary", "Decimal", "Hex", "Exponential", "Engineering"]

    control.limitLow double = 0

    control.limitHigh double = 0

    valueAlarm.lowAlarmLimit double = 0

    valueAlarm.lowWarningLimit double = nan

    valueAlarm.highWarningLimit double = nan

    valueAlarm.highAlarmLimit double = 2

 

From reading the docs, I gather that before the valueAlarm_t type, there used to be an alarmLimit_t type, which had an “enable” field – but currently I don’t see a way to do this besides possibly resetting the valueAlarm limits, and I don’t want to do that.

 

Can anyone recommend a way to disable the alarm at the IOC, given these coditions?

 

Thanks!

 

• Dave Bracey, Fermilab AD

-- 

Pierrick Hanlet

Fermi National Accelerator

Accelerator Front End Controls

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+1-312-687-4980 -- mobile

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