[chrony-users] Strange "loss of PPS lock"

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I have a couple of installs where a PC is synchronized to PPS.
The PPS signal is connected to DCD on a serial port and ldattach is used
to attach it to /dev/pps0.  chrony.conf has:

refclock    PPS /dev/pps0 refid PPS prefer

and a couple (3-4) external NTP servers as absolute time reference.
That normally works just fine.  PPS source is marked with * and offset is
within 20us or so.

"but sometimes" it loses lock.  The PPS source is marked with x and an NTP
server is selected and tracked.  an hour later or so, the situation automatically
rectifies itself.  I notice this because the installation is monitored using Nagios
and NTP stratum is one of the monitored parameters.  It goes from 1 to 2.

What can be the cause of this?  The jitter value displayed in chronyc sources
remains within 5-20us all the time.  But the offset to PPS can go as high as 2ms
during this.  It may be that the combined offsets of the NTP servers as seen by
chrony are closer to another than the PPS source is, but still I don't want them to
get selected as long as the PPS can be locked and tracked.  In some locations
there even is a separate SHM source, derived from serial comms with the reference
to check if it is in sync, configured as "lock" (which itself is configured "noselect"),
but it still happens.  That "lock" reference is in-lock at those times.

Only thing is that this is "an old version" (3.2 from Debian distro) version.
Is it a known problem that has been fixed after that?


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