Re: [chrony-users] How to use a "PPS" with freq higher than 1Hz?

[Vincenzo Miceli <vincenzomiceli@xxxxxxxxxxx>]

Thanks Miroslav,

I was able to get the PPS to start by removing the "lock GPS" and using a public NTP. I guess the NMEA coming from the GPS has too much jitter then? I don't fully understand though as the NMEA is always coming once a second and at higher frequencies (I would think) the chrony algorithm has to deal with more samples closer together and can still sample the GPS once a second and compare that with the 10 pulses per second, maybe with the PPS-GPS separation still working off the 200msec limit...  I'm sure there are good statistical reasons though 🙂🙂

Cheers,

Enzo

---

From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
Sent: Tuesday 30 March 2021 13:58
To: chrony-users@xxxxxxxxxxxxxxxxxxxx <chrony-users@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [chrony-users] How to use a "PPS" with freq higher than 1Hz?

 

On Tue, Mar 30, 2021 at 12:10:33PM +0000, Vincenzo Miceli wrote:
> refclock PPS /dev/pps0 refid PPS lock GPS precision 1e-9 poll 3 offset 0.0 rate 5 dpoll -3 prefer
>
> but monitoring with "watch chronyc sources -v" shows no readings from PPS

A higher PPS rate requires a more accurate and stable source for
"locking". For a 5Hz PPS it needs to fit within 40ms. Your screenshot
shows "+/- 100ms". That's too much. You will need to set a smaller
delay for the GPS source.

If that GPS source is not stable enough, you might need to disable the
"lock" option, or use an NTP server, in order to start the PPS refclock.

--
Miroslav Lichvar


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