[time-nuts] Linux PPS clues?

Gary E. Miller gem at rellim.com
Thu Oct 20 14:11:08 EDT 2016

Yo Ilia!

On Thu, 20 Oct 2016 07:52:10 +0000
Ilia Platone <info at iliaplatone.com> wrote:

> I quickly read the gpsd howto and it explains what I want to do using 
> kpps on a raspberry. From there I can see a typical accuracy of 1uS,
> but the informations of the live graphs page are precise down to the
> ns: are these averaged?

Well, that is a complicated question.  The graphs are directly from the
ntpd logs.  No modification to the data except scaling.  But ntpd
itself is sort of a big PLL.  Also the way ntpd handles PPS is somewhat
complicated.  There is an algorithm for ignoring outlier pulses, and the
accepted puless are averaged in the mipoll interval before being
logged or input into the PLL

But, bottom line, you can pretty much expect the RasPi sysclock to be
stable and accurate, to one standard deviation of better than 1 µs. 90%
of the time, to better than 2 µs.  Better than 5.5 µs for 98% of the

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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