| Re: [chrony-users] Possible bug in PPS support |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Possible bug in PPS support
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Mon, 23 Oct 2017 19:44:06 +0200
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On Mon, Oct 23, 2017 at 10:24:54AM -0700, Bill Unruh wrote:
> On Mon, 23 Oct 2017, Rob Janssen wrote:
> > You don't support my calculation that if the clock apparently wandered
> > away 3400us
>
> Again, no evidence of that 3400 us.
If I understand it correctly, 3.4ms was the offset of the NTP source
13 hours after the PPS stopped working. The stddev of the NTP source
from sourcestats is ~50 microseconds, so if the offset was originally
better than 1.6ms (there are 3 different sources in the original
report with -0.1ms, 1.5ms, 1.5ms offsets), it drifted at least by
~1.8ms in that time.
If there was a significant change in the temperature, the error gained
in 13 hours could be much larger. On one of my servers with PPS I see
that the frequency offset can change by 0.5 ppm in just few seconds.
--
Miroslav Lichvar
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