[ntp:questions] Strange jumps in PPM

mike cook michael.cook at sfr.fr
Wed Aug 21 08:48:24 UTC 2013

Le 21 août 2013 à 09:14, A C a écrit :

> On 8/20/2013 23:53, mike cook wrote:
>> Le 21 août 2013 à 08:33, mike cook a écrit :
>>> Le 21 août 2013 à 08:03, A C a écrit :
>>>> Ok, so I saw the below event in the loops on my system which is
>>>> controled by ATOM, SHM, and several internet servers.
>>>> I suspect it has to do with the GPS PPS output glitching during
>>>> extreme satellite events (bad constellation arrangement, fringe
>>>> signal, etc.)
>>>> Is there a way to have ntpd ignore the PPS quickly if it spins
>>>> out of control?  The system recovers fairly quickly and the clock
>>>> doesn't go too far out but it would be nice to avoid these
>>>> jumps.
>> I realize now that I didn't respond to the question :-( .  AFIK there
>> are no knobs available to do this. It would be nice to be able to
>> specify maximum acceptable offset or jitter by clock.
> That would be very useful to have.  I could easily avoid these hiccups since they're so wildly different and sudden compared to the normal operation.

   It might be accomplished automatically by establishing a Figure Of Confidence over the life of the clock which could be the average of the previous n offsets and exclude the clock if an offset exceeding x times the average occurs. The clock offsets would then be monitored and the clock included when/if the offset over n samples returned to the previous average.

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