Re: PPS in GPSD vs Chrony

[Gary E. Miller]

Yo Gary!

> > Here is a quick test comparing the PPS rate of 32 and 1 Hz. The
> > polling interval didn't change (1 second) and it was running on an
> > idle system (an Orange Pi PC). The RMS offset value is about 4.7 ns
> > vs 13.5 ns, so the improvement is not as good as the square root of
> > the rate ratio, but still significant.
> > 
> > https://i.imgur.com/9E7zUai.png  
> 
> If the poll rate stays at 1Hz then why does a higher "PPS" help?
> Maybe it keeps chronyd (I assume you are using chronyd) fresh in the
> CPU cache and running on its own core.  This is an odd one.

Hmm, how does the time daemon (gpsd, chonryd, ntpd) know which of the
32 pulses is the top of the second?  NMEA time is very unlikely to be
better than 30 ms.

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

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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