[chrony-users] Chrony gets out of sync regularly

[Gabriele Coppi <gabriele.coppi@xxxxxxxxx>]

I am having some issues running Chrony with only GPS+PPS (coming from the GPS) on RPi 4. At the startup gpsd starts running with no particular issue and I got GPS and PPS solution with no problem checking gpsmon. I have installed chrony to use the GPS and PPS as a time sources to keep the clock in sync with those. Compared to the default chrony config file I commented all the debian pool server and the rtcsync since the RPi does not have a RTC. I also added the following lines:

refclock SHM 0 precision 1e-1 delay 0.5 refid GPS
refclock SHM 1 precision 1e-7 refid PPS

The chronyc sources command shows that after a settling time the PPS source is chosen as the best and the GPS is discarded. This situation is pretty stable for 17min and then gets out of sync for 17min and then gets in sync again for 17min. During the out of sync, so when both sources are discarded, the sources still have a reach of 377.

Looking at the tracking.log I can see that at the beginning and the end of the each 17min session I have a 0.0.0.0 IP Address as source.

Any idea why I have this regular behaviour between sync and out of sync?

Gabriele