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

Dave Hart hart at ntp.org
Thu Mar 1 19:51:14 UTC 2012


On Wed, Feb 29, 2012 at 17:23, alex n <alexvm22 at gmail.com> wrote:
> If I disconnect GPS receiver ntpd stopped (reach value is decreased to 0).
> PPS is incoming from FPGA. Perhaps I need some config settings?
>
> my ntp.config
>
> #NMEA + PPS
> server 127.127.20.0 mode 16 prefer minpoll 4
> fudge 127.127.20.0 flag1 1 flag3 1 refid NV24

As an aside, in an integrated NMEA+PPS setup such as above, you don't
need (and probably don't want) prefer.

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:

server 127.127.20.0 mode 16 prefer minpoll 4
fudge 127.127.20.0 refid NV24

server 127.127.22.0 minpoll 4
fudge 127.127.22.0 flag3 1

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

Cheers,
Dave Hart


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