[ntp:questions] NTP, GPSD & PPS
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?
More information about the questions