[ntp:questions] NTP, GPSD & PPS

Paul tik-tok at bodosom.net
Tue Dec 9 20:51:51 UTC 2014


On Tue, Dec 9, 2014 at 12:24 PM, David Taylor <
david-taylor at blueyonder.co.uk.invalid> wrote:

> Paul, does the NMEA (or ATOM) driver solve the problem of having perhaps a
> couple of hundred milliseconds peak-to-peak jitter in the GPS serial data,
> thereby preventing NTP using the PPS source?


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.


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