[ntp:questions] Single GPS/PPS time source gets marked as a falseticker

unruh unruh at wormhole.physics.ubc.ca
Thu Jul 14 14:04:26 UTC 2011


On 2011-07-14, Rob <nomail at example.com> wrote:
> Michael Eder <meder at whoi.edu> wrote:
>> We have looked at our GPS on a scope, the PPS it is dead on and the NMEA
>> (just one sentence) is also reliable with about a 680 ms latency and 10 ms
>> jitter.
>
> Again, are you using gpsd?
>
> If so, you may want to try removing the (huge) 680ms offset inside gpsd
> instead of in ntpd.
> There is a place in the code where a fixed offset is added to time obtained
> using NMEA (because the gpsd author does not want configurable items) and
> it cannot be correct for every possible receiver.
>
> Again, it is better to switch from NMEA to the native binary protocol
> of the receiver.

Why? That native binary will also suffer from large latency (the serial link
is slow no matter what is being sent over it) and probably also fairly
large jitter. And it suffers from the huge downside of your having to
learn a whole new language.




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