I think Richard is correct.
The sync state depends on your system.
On my setting a 'sync' is when the correction is bellow 100 nanoseconds, when
it is usually bellow 10 nanoseconds and I except to have it stable for 5
seconds long.
There is no generic sync.
So each user need to define a 'sync' that match to its system needs.
Erez
-----Original Message-----
From: Miroslav Lichvar <mlich...@redhat.com>
Sent: Thursday, 17 March 2022 08:52
To: Martin Pecka <pecka...@fel.cvut.cz>
Cc: linuxptp-devel@lists.sourceforge.net
Subject: Re: [Linuxptp-devel] [PATCH] Add non-portable management option to
query the servo state (via SERVO_STATE_NP).
On Wed, Mar 16, 2022 at 11:55:27PM +0100, Martin Pecka wrote:
> > People naively want a simple Boolean flag. However, the reality is
> > that there is no simple answer to the question, is my computer
> > synchronized.
> Well, that is actually what people expect from a time sync daemon.
> Chrony has it (* or + in `chronyc sources`),
* or + only tells you whether a time source is selected for synchronization,
nothing about the clock actually being synchronized, no matter what definition
you have for that. It's a common misconception. In PTP that would be a port
being in the slave state.
On systemd-based distributions there is a "time-sync" target, after which can
be ordered start of services that require "synchronized"
clock. With the chrony-wait service, the time-sync target is reached when the
reported remaining correction of the clock is less than 100 milliseconds.
With ptp4l or phc2sys, you would just wait for the first non-zero offset
smaller than some value (e.g. 1000 nanoseconds).
> systemd has it ("System clock synchronized: yes" in timedatectl)
'yes' is reported by timedatectl when the maxerror value of the system clock
(from adjtimex() or ntp_gettime()) is smaller than 16 seconds.
That normally happens on the first update of the clock. timedated/ctl doesn't
know what is actually controlling the clock. This works even with ptp4l (if SW
timestamping) and phc2sys.
--
Miroslav Lichvar
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