Re: [chrony-users] kernel PPS troubleshooting

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On Tue, Nov 26, 2013 at 08:49:19PM -0500, Battocchi, Scott L. wrote:
> Bill,
> Thanks for taking an initial look.  I've added my system to our network to compare our GPS time with the general NTP pool and it looks like our GPS could be right on the edge of that 0.4s window.  I'm going to let it run for a bit like this and report back after trying a larger offset for our SHM refclock.  The receiver I am using is an MTK3339 if anyone else has a standard offset they use (default speed and strings (9600 8n1 with GGA GSA RMC VTG and VSG enabled).

Yes, from the log it looks like the SHM and PPS sources are too far
from each other (large offdiff value). Also, the GPS source might be
too jittery to be used reliably as the locking reference for PPS.

One way to find out which one is wrong is to add a good NTP source as
the reference, add the noselect option to the GPS and PPS sources
(without any locking) and observe the offset values in the refclocks
log or chronyc sourcestats output.

Miroslav Lichvar

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