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<== Date ==> <== Thread ==>

Subject: RE: which time/timestamp format to use for an EPICS facility?
From: Di Maio Franck <Franck.DiMaio@iter.org>
To: "Konrad, Martin" <konrad@frib.msu.edu>, EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Mon, 9 Dec 2013 16:01:48 +0000
Hello Konrad

For immediate conversion (option 1), the simplest is to get the TAI/UTC offset from the GMC through the PTP hardware (PCI/PXI board or on-board chipset).  We tested that on our NI PXI boards and on on-board Intel chipsets. It works in both cases but we don't use.

For later conversion (option 2), the software needs a copy of the leap second table (with all history). This table can change twice a year but can be cached on the site network. This is the procedure we use.

Franck

-----Original Message-----
From: Konrad, Martin [mailto:konrad@frib.msu.edu] 
Sent: 09 December 2013 16:33
To: EPICS Tech Talk
Cc: Di Maio Franck; Benoit
Subject: Re: which time/timestamp format to use for an EPICS facility?

Hi Franck,
it's good to hear that ITER is prefering TAI over UTC as well :-)

> Actually, we are suppressing POSIX UTC from timing boards' drivers 
> only & convert to UTC for applications (inc. EPICS records).
What exactly does converting from TAI to UTC for an EPICS record mean? I see two ways to do that:

1. Convert from TAI to UTC. This requires leap second information on all EPICS IOCs.
2. Just copy the TAI timestamp into an EPICS timestamp and let the clients do the conversion. Since TAI has no leap seconds this should work smoothly. But strictly speaking this is against the definition of EPICS timestamps (which are defined to be in UTC - see epicsTime.h).

If you chose 1.: Do you periodically download the leap second information from a central server into all your IOCs? How do you deal with the fact that EPICS timestamps do not have a representation for leap seconds?

If you chose 2.: How do you make sure all your clients are converting time in the right way (including leap seconds)? Do you have any procedures in place for that?

Thanks a lot,

Martin

--
Martin Konrad
Control System Engineer
Facility for Rare Isotope Beams
Michigan State University
640 South Shaw Lane
East Lansing, MI 48824-1321, USA
Tel. 517-908-7253
Email: konrad@frib.msu.edu


References:
which time/timestamp format to use for an EPICS facility? Konrad, Martin
Re: which time/timestamp format to use for an EPICS facility? Konrad, Martin
RE: which time/timestamp format to use for an EPICS facility? Di Maio Franck
Re: which time/timestamp format to use for an EPICS facility? Benoit
Re: which time/timestamp format to use for an EPICS facility? Konrad, Martin

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