[ntp:questions] NTP, GPSD & PPS

Paul tik-tok at bodosom.net
Tue Dec 9 21:06:24 UTC 2014

On Tue, Dec 9, 2014 at 3:17 PM, Nomen Nescio <nobody at dizum.com> wrote:

> The PPS pulses and NMEA sentences need to be "close enough" before
> ntpd will accept them. Usually that means the the NMEA sentence needs to
> arrive during the bounds of the second it is naming.

If that's not happening your GPS is buggy and should be fixed or replaced.
However it's not enough for NTP.  The timestamps need to be consistently in
the same acceptable window.  Some units are quite bad at this so ...

> It is not uncommon to have to adjust the offset to fix this problem.

you can't get a reliable lock with a static offset.

> You can't use the PPS without something to name the seconds. This can
> either be the NMEA sentences provided by the ATOM driver

Refclock 22 (ATOM) doesn't provide NMEA.

People that want to use NMEA really should buy a GPS that can deliver
stable sentences.
 *    .FURY.           0 l    1    8  377    0.000    0.008
not this:
x127.127.20.0    .AMTK.           0 l    4    8  377    0.000   28.560

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