Re: [chrony-dev] pps source is still marked as synchronised when no absolute clock sources are available

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Wed, Jan 20, 2010 at 04:36:17PM +0100, Hattink, Tjalling (FINT) wrote:
> I agree with you that chrony will be able to keep time between the pps
> pulses. But in my situation I cannot blindly trust the incoming PPS
> signal
> being the correct time. When the GPS card has no lock it keeps
> generating
> PPS pulses from its own oscillator, but it will be free running and
> drifting
> fast as no GPS corrections come in. So somehow I have to tell chrony not
> to
> trust the PPS source anymore when GPS lock is gone. I used to do this
> for
> ntpd by making the SHM clock unreachable, but it works differenty in
> chrony.

I agree that sometimes it may be dangerous to keep using PPS signal
without any reference, but sometimes it's useful. When local stratum
is enabled, you can even use PPS signal without any reference and
correct the seconds by wristwatch if needed.

Ideally, this would be configurable. Perhaps a refclock option to bind
it with another one. This would also allowed to use PPS signal
immediately without waiting for first sync.

> If you would like to always trust any incoming PPS signals, even if no
> absolute reference source is available, maybe I can solve it by
> implementing a chronyc command to disable specific reference clocks. 

Suspend/resume refclock commands would be certainly useful also in
other cases.

-- 
Miroslav Lichvar

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