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

[Vincenzo Miceli]

Thanks Miroslav,

actually, my GPS module can be setup to issue NMEA sentences at a user specified frequency, so I think I'll start with 2Hz then see how high can it go... I'll report back when I have new results.

Cheers
Enzo
________________________________
From: Miroslav Lichvar <***@redhat.com>
Sent: Wednesday 31 March 2021 10:21
To: chrony-***@chrony.tuxfamily.org <chrony-***@chrony.tuxfamily.org>
Subject: Re: [chrony-users] How to use a "PPS" with freq higher than 1Hz?

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 🙂🙂

If the NMEA rate stays at 1 per second (some receivers can be
configured to report at a higher rate) then you would need to increase
maxlockage of the PPS refclock.

The locking feature uses just the latest sample. In theory it could
use a longer-term average, but I'm not sure if it's worth the
complications.
--
Miroslav Lichvar