RE: wrong timestamps in monitors

["Dalesio, Leo" <dalesio@bnl.gov>]

There is no plan to make a time stamp relative to the update of a single field. What is the demand for this? What is the situation where this is required?

-----Original Message-----
From: tech-talk-bounces@aps.anl.gov on behalf of Benjamin Franksen
Sent: Thu 1/29/2009 8:46 AM
To: tech-talk@aps.anl.gov
Subject: wrong timestamps in monitors
 
Hi,

I think this is a known issue, it is at least as old as 3.13.9. EPICS posts 
CA events when a non-VAL fields get written to, and it does so 
independently of record support. There are two cases:

- If the field does not have the PP property, then the record is not 
processed as a result of the put, and the CA event is posted with the old 
timestamp.

- If the field /does/ have the PP property, then the record gets processed 
as a result of the put, which woudl update the record's timestamp, but 
processing comes /after/ EPICS base posts the event, thus the event has the 
wrong (old) timestamp.

It should be clear that this means one should /not/ trust the history of 
value changes as e.g. reported by the channel archiver (or simply the 
output of camonitor) whenever the PV in question references a non-VAL 
field. At least not w.r.t. the reported timestamps.

Is this going to be addressed any time soon?

Cheers
Ben
-- 
"Programming = Mathematics + Murphy's Law" (E.W.Dijkstra)

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