Re: Understand put requests

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

The details of what happens when you write a new request before the previous one is complete can depend on the record type and device/driver support.  But in general I think it will queue at most one new request if the record is currently processing a previous request.

Your client can use ca_put_callback to ensure that a previous request is complete before issuing another one.

Mark

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Zhang, Tong via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, May 30, 2025 8:03 AM
To: Liu, Wanming <wmliu at anl.gov>
Cc: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: RE: Understand put requests

 

Hi Wanming,

 

Normally, the device is working well with caput under human interaction, but just sometimes does not respond (got stuck on the last setpoint) to the optimization algorithms issued put requests.

 

Cheers,

Tong

 

From: Liu, Wanming <wmliu at anl.gov>
Sent: Thursday, May 29, 2025 9:56 PM
To: Zhang, Tong <ZhangT at frib.msu.edu>
Subject: Re: Understand put requests

 

[EXTERNAL] This email originated from outside of FRIB

I would try to use caput or pvput in a terminal to make sure it response before try to do it with a script or whatever.

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Zhang, Tong via Tech-talk <tech-talk at aps.anl.gov>
Sent: Thursday, May 29, 2025 3:55 PM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Understand put requests

 

Dear Colleague,

I'm building something to deal with the real device controls and came
across some issues. Some power supply devices could not be changed
during the running of optimization routines, which is executing the CA
put requests repeatedly, not very fast, a few seconds per iteration. 

Since I'm not the device IOC creator, my understanding is that possibly
the specific device does not respond to the request promptly, the
questions are:

- How does a device control IOC to respond a new incoming change
request if it's still processing one?
- Is there any way to know that the PV is ready to take a new change
request?
- Or is there any way to signal the PV to ignore any processed request
but take the latest request?

To my point of view as an application developer, the expected behavior
is the device only process the latest request and drop the one that is
under processing. But before talking with the responsible engineer, I
would like to fully understand this problem.

Appreciate your help.

--
Tong Zhang <zhangt at frib.msu.edu>
Facility for Rare Isotope Beams, Michigan State University