On 18/06/2013 08:41, Miroslav Lichvar wrote:
[]
IIRC, the one second interval is used only to collect the SHM samples
and store them in a buffer. In the minpoll/maxpoll interval the
collected samples are processed in a median filter and one final
sample is used to update the clock. This improves the jitter.
Yes, that makes sense.
I'll try setting it to 4, as a test, and see whether anything changes.
The difference with NTP sources is that changing the poll interval
affects also the jitter as there will be a different number of samples
in the filter.
I've put a couple of graphs here:
http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#user-mode
which show a drop of RMS offset from around 5 microseconds to 4
microseconds and a drop in averaged jitter from just below 7 to just
above 5 microseconds, when the minpoll was changed from 3 to 4.
--
Cheers,
David
Web: http://www.satsignal.eu
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