[ntp:questions] NTP, GPSD & PPS

David Taylor david-taylor at blueyonder.co.uk.invalid
Wed Dec 10 09:26:34 UTC 2014


On 09/12/2014 20:51, Paul wrote:
[]
> As I mentioned previously it's still possible to use refclock 1 (LOCAL).
> The driver is claimed to be deprecated but it's still present in 4.2.7 so
> presumably will be in 4.2.8.
>
> server 127.127.22.0 minpoll 3 maxpoll 3
> fudge  127.127.22.0 stratum 0
> server 127.127.20.0 minpoll 3 mode 16 prefer
> fudge  127.127.20.0 time2 0.5 flag4 0
> server 127.127.1.0 minpoll 3 prefer
> fudge  127.127.1.0 stratum 12
>
>
> Note that in this configuration the LOCAL clock isn't *undisciplined*.
> You're good until you restart.  If you(sometimes) have internet access you
> can "prefer" another server to number the seconds.  If you never have
> internet access you'll have to wait until NTP accepts timestamps from the
> GPS.  This will eventually happen with an 18x given a descent sky view.
>
> My NTP appliances manage to number seconds via NMEA or the equivalent  so
> while folks are fixing things they could fix this too.

There's actually an elegant (I think) piece of code in the Windows port 
of NTP which uses the PPS time (measured via interrupt) as the timestamp 
of the first NMEA sentence received, thus removing all the offset, and 
the offset variation, from the NMEA sentence timing.  Perhaps something 
like this could be a more generally available option for GPS/PPS systems?

-- 
Cheers,
David
Web: http://www.satsignal.eu



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