| Re: [chrony-users] PTP as chrony time source and leap seconds |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] PTP as chrony time source and leap seconds
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Mon, 10 Aug 2020 10:05:23 +0200
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On Fri, Aug 07, 2020 at 12:48:14PM +0200, Olaf Frączyk wrote:
> Hello,
>
> I would like to use PTP as one of chrony time sources. The chrony would
> discipline local clock and serve NTP to clients.
>
> I have found that one needs to specify number of leap seconds in config file
> when using PHC.
There is also the "tai" option to automatically correct refclock
samples for the TAI-UTC offset.
> Why is it necessary? The PTP protocol includes TAI-UTC offset.
PTP does, but chrony doesn't speak PTP.
> I saw that a possible solution would be to synchronize system clock using
> ptp4l with phc2sys and use local clock as chrony time source - however it
> may cause problems if PTP synchronization fails - and chrony will not know
> that local clock is unsynchronized. That's why I would like to use PTP
> source in chrony directly.
It's the opposite. The PHC refclock may be problematic when PTP stops
working. With phc2sys in the automatic mode (-a option) that shouldn't
be a problem.
My recommendation is to use phc2sys -a -E ntpshm and configure chrony
to use that SHM as a reference clock. In linuxptp there is a
timemaster program, which can be useful when you have multiple PTP
sources and don't want to deal with all the different programs that
need to be configured and started.
--
Miroslav Lichvar
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