[ntp:questions] Running ntpd with PPS precision signal only

alex n alexvm22 at gmail.com
Mon Mar 5 18:15:03 UTC 2012


Hi Dave,

Thanks for your help.

> Assuming you are not disconnecting the PPS by disconnecting the NMEA,
> if you want the PPS to survive NMEA outage you'll likely need to
> switch from unified NMEA+PPS driver to NMEA-only and PPS-only:

NMEA and PPS drivers work fine, but sometime after power on a time
diffrenece between NMEA and PPS is too big (about 3 secs) and I have

xGPS_NMEA(0)     .NV24.           0   31d   16  377    0.000  2510.04   8.180
xPPS(0)                .PPS.            0   31d   16  377    0.000
-481.79   3.693

I think there isn't a synchronization between NMEA and PPS signals
though I found and set time2 properly.

> If that doesn't do the trick, also add one or more network servers
> with "prefer".

Unfortunately I can't use any network servers on my embedded system...

>I'm unsure at the moment if the PPS driver requires a
> reachable prefer peer continuously, or only to bootstrap.  Also you
> may need a fudge time2 on the NMEA to offset its end-of-sentence
> timestamps to be closer to the preceding PPS timestamp -- the PPS
> driver requires the prefer peer(s) get the system clock offset
> relative to the PPS under 0.4s before the PPS is engaged.

Thanks,
Alex.


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