Re: [chrony-users] kernel PPS troubleshooting

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On Mon, Dec 02, 2013 at 02:59:05PM -0500, Battocchi, Scott L. wrote:
> Since we will not have access to a network time source and will be relying on GPSD/NMEA to get us in the correct ballpark on system startup, is there another configuration option we can try to minimize the snapping back to GPS so quickly?

You can mark the NMEA source as noselect and still lock the PPS source
to it. The PPS samples will be ignored when NMEA is off by more than
0.2 seconds, but according to your graphs that shouldn't happen very

> The three attached plots are:
> 4hr_offsets:  Hours 0-4, offsets straight from statistics.log
> 4hr_offsets_PPSadjusted:  Hours 0-4, adjusted offsets assuming PPS was always 0 and using the most recent PPS value to adjust the actual offset in statistics.log
> Syncsource_PPSadjusted:   Hours 2-4, same data as PPSadjusted but with background highlighted according to active sync source from tracking.log

Nice graphs!

> I have the full console output as well with debugging enabled and am trying to figure out how best to parse and analyze it.  One thing I notices in comparison to my previous run is that all of the ignored PPS samples are coming from line 465 in refclock.c:
> refclock.c:465:(RCL_AddPulse)[28-14:20:00] refclock pulse ignored second=0.999999657 sync=0 dist=1.500000000

Hm, that's weird. Do they all have the same sync and dist value? Could
you please attach corresponding parts of the tracking, refclock and
statistics logs around the time when the PPS source is dropped?

> and not line 440 like they were on the previous run:
> refclock.c:440:(RCL_AddPulse)[26-18:03:56] refclock pulse ignored offdiff=-0.313099609 refdisp=0.041061551 disp=0.022734546

They are ignored in a different place because the lock option
wasn't used this time.

Miroslav Lichvar

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