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<== Date ==> <== Thread ==>
Subject: Re: issue of getTimeStamp from EVR
From: Ralph Lange via Tech-talk <tech-talk at aps.anl.gov>
To: EPICS Tech Talk <tech-talk at aps.anl.gov>
Date: Fri, 7 Jul 2023 17:29:21 +0200
On Fri, 7 Jul 2023 at 17:17, Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> wrote:

In many cases, reliance on system time (via. NTP) can be entirely acceptable.
However, if a more precise wall clock time is desired, you could investigate
the  "NTPD Time Source" section.  This allows the system clock to be sync'd
through the EVR, which has much lower jitter than NTP.

I second that.

For the ITER fast controllers, we found that going to the PXIe timing card to read the timestamp is too slow and adds a lot of jitter.
Instead, we're running a PTP daemon that synchronizes the system clock to PTP. This is conceptually similar to what ntpd or chronyd are doing, but PTP allows for a better synchronization.
Result:
- EPICS just reads the system clock and gets a precise, low-jitter time stamp using a fast call.
- IOCs on fast controllers and virtualized not-so-fast hosts run exactly the same code. It's the system clock below that is better on a fast controller with PTP. 

Cheers,
~Ralph

References:
issue of getTimeStamp from EVR Di Wang via Tech-talk
Re: issue of getTimeStamp from EVR Michael Davidsaver via Tech-talk
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