| Re: [chrony-users] kernel PPS troubleshooting |
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On Thu, Nov 28, 2013 at 11:11:18AM -0800, Bill Unruh wrote:
> On Thu, 28 Nov 2013, Miroslav Lichvar wrote:
> >That looks similar to what I see with with a Garmin 18x LVC. This is a
> >capture 30 hours long I did some time ago (the NMEA source's offset
> >value was set to 0.5):
> >
> >http://mlichvar.fedorapeople.org/tmp/18x_nmea.png
>
> Is this the nmea time or the PPS time? And is the vertical axis seconds or
> milliseconds?
That's the NMEA time (as provided by gpsd) when the clock was
synchronized to PPS. It's unfortunately in seconds. I think it was
with 115200 baud rate.
> The problem in his case is that the PPS signal is occasionally
> (but far too often) off by almost .3 sec. That is rediculous. And it is only
> when the gps-nmea and the PPS are the only sources.
He said chronyd was switching between the PPS and GPS sources, so the
0.3s spike could be just the PPS-NMEA offset. The other graph with
chronyd using NTP sources doesn't seem to have this problem.
--
Miroslav Lichvar
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