Experimental Physics and
Industrial Control System

Ah sorry, I misread about the TIME field I thought it was only not readable but would still be writeable.  Currently we are using a labview driver to talk with some of the NI hardware and I don’t have direct access over how they implemented it to use the device support to set it.  It seems the driver has the ability to caput and is what we have been doing to add data to the waveform records we need.  Is the best route then to

 

keep TSE=-2 ( I assume this still needs to be set so that the time field doesn’t get set by another means?)

create a PV to hold the timestamp from the digitizer

have a FLNK push the timestamp to the TIME field of the record A (is this possible?)

have TSEL copy that timestamp to all other records

 

From: Johnson, Andrew N. <anj at anl.gov> 
Sent: Monday, December 14, 2020 2:53 PM
To: Manoussakis, Adamandios <manoussakis1 at llnl.gov>
Cc: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: Re: Timestamping Confusion

 

Hi, 

 

On Dec 14, 2020, at 4:43 PM, Manoussakis, Adamandios via Tech-talk <tech-talk at aps.anl.gov> wrote:

 

Partial success so far, I was able to get the TSEL to grab the timestamp from another record that was set by TSE default 0 (sys clock I think this is?).  When I set TSE to -2 can you not write to the TIME field of a record like this

 

Caput mydevice:abc.TIME 2020-12-14 14:38:49.021827

 

I was hoping to simulate my digitizer setting the timestamp in my waveform record TIME field.

 

Sorry, the TIME field is not directly accessible through Channel Access at all, other than being readable as metadata (i.e. part of a DBR_TIME_xxx or similar data type). You can’t read or write a .TIME field directly, generally only a device support or a link type can set the TIME field of a record. The point of setting TSE to -2 is to tell the record that the device support has already set the TIME field and the record should not overwrite it with the current wall-clock time.

 

- Andrew

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Manoussakis, Adamandios via Tech-talk
Sent: Monday, December 14, 2020 1:32 PM
To: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: RE: Timestamping Confusion

 

Thank you both for the insight, it seems best for us to go a similar path of using TSEL to copy the timestamp from the digitizer to each of our waveform records and using TSE set to -2 to stop the IOC from overwriting the time field (please correct me if I am wrong on this). I think I just need to understand the best way to get the first timestamp and then use TSEL to pass it along to the other records.

 

Ralph when you stated to have the digitizer send the timestamp with the data, would I just have my digitizer set the TIME field in the waveform record then?

 

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Ralph Lange via Tech-talk
Sent: Saturday, December 12, 2020 5:25 AM
To: EPICS Tech Talk <tech-talk at aps.anl.gov>
Subject: Re: Timestamping Confusion

 

On Fri, 11 Dec 2020 at 22:33, Manoussakis, Adamandios via Tech-talk <tech-talk at aps.anl.gov> wrote:

Thanks for the comments Michael, when you are dealing with hundreds of waveform records and the timestamps are being taken when each record is processed (I would assume these would all be off by some delay if multiple softIOCs are running) do you then just have a master time waveform to lineup all your other signals to t0?  It seems the digitizer would have a time stamp of t0 for all of its signals but the epics records would not all align at the same timestamp since each one isn't processed at t0 to be timestamped.

 

The EPICS Device Support needs to know the timestamp t0 (preferably sent with the data by the digitizer) and write it to each record's timestamp when it updates the record.

In that case, by configuring their TSE to -2, all waveform records can use the digitizer timestamp. That timestamp can even be forwarded (using TSEL) through post-processing chains, so that processed data may still use the timestamp that the digitizer sent with the raw data at the beginning of the chain.

 

Cheers,
~Ralph

 

-- 

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