Experimental Physics and
Industrial Control System

I have several work a rounds.  Right now, we store a timestamp PV as the acquisition time and then the data in additional PVs.  The correct way is to have the DAQ system call the ca_put immediately (the data is coming in at a 5 Hz level). There are others which collaborators have suggested as well. It just seemed unnecessarily complicated and un-natural given that there exists a location in the record for the time already.

It is of course possible to write some C code for the IOC that will let you do that, but the fact that it isn’t easy is an indication to me that there may a better way to do what you’re looking for.

Paul

Hi Paul,

On Jan 25, 2021, at 4:41 PM, Reimer, Paul E. via Tech-talk <tech-talk at aps.anl.gov> wrote:

The "acquisition time" is a trigger generated elsewhere and served by equipment that, at this time, can't talk directly to EPICS.  The best solution is to have the acquisition system talk directly with EPICS--I argued for this--but that is not what I have. The data is essentially buffered (with and acquisition timestamp) and then handed off to a system that talks with EPICS.

Are there any other protocols or APIs that an IOC might be able to use to communicate with the system, and what kinds of data sizes and rates are involved in the data transfers?

EPICS systems don’t generally use Channel Access clients as agents for acquiring data, and as a result we don’t have an easy way to put an EPICS timestamp into a Channel Access PV. It is of course possible to write some C code for the IOC that will let you do that, but the fact that it isn’t easy is an indication to me that there may a better way to do what you’re looking for.

If you could describe the larger problem to the community (i.e. to this list) we might be able to recommend alternatives that could turn out to be faster and easier – no promises, but it’s worth a try. 

- Andrew

On 1/25/21 16:34, Arnold, Ned D. wrote:

> I would like the timestamp field for that PV to reflect the acquisition time rather 
than the time that the ca_put(DBR_LONG, stchid, &iParVal) routine is 
called. 

Is the "acquisition time" a user defined time, an event within the IOC, or an external trigger generated from somewhere else?  

  Ned

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Reimer, Paul E. via Tech-talk<tech-talk at aps.anl.gov>
Sent: Monday, January 25, 2021 02:14 PM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Altering timestamp of softIOC PV

 

Hello,

Is it possible to alter the timestamp field of a PV? Specifically, I 
have a situation in which data is recorded by a computer, but might not 
be put into EPICS immediately (few sec delay is possible). I would like 
the timestamp field for that PV to reflect the acquisition time rather 
than the time that the ca_put(DBR_LONG, stchid, &iParVal) routine is 
called.  I note that the time field is of type "NOACCESS" in the manual.

Thanks,

Paul

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Paul E Reimer               +1-630-252-4037 (Office)
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Argonne National Laboratory +1-630-344-9207 (mobile)
9700 S Cass Ave             reimer at anl.gov
Lemont, IL  60439 USA.      he/his/him

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Complexity comes for free, simplicity you have to work for.

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Paul E Reimer               +1-630-252-4037 (Office)
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Argonne National Laboratory +1-630-344-9207 (mobile)
9700 S Cass Ave             reimer at anl.gov
Lemont, IL  60439 USA.      he/his/him

Replies:

Re: Altering timestamp of softIOC PV Johnson, Andrew N. via Tech-talk

References:

Altering timestamp of softIOC PV Reimer, Paul E. via Tech-talk

Re: Altering timestamp of softIOC PV Arnold, Ned D. via Tech-talk

Re: Altering timestamp of softIOC PV Reimer, Paul E. via Tech-talk

Re: Altering timestamp of softIOC PV Johnson, Andrew N. via Tech-talk

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