[ntp:questions] How to debug PPS?

David Lord snews at lordynet.org
Sun Apr 25 01:07:38 UTC 2010

Chaofu Chen wrote:
> To David: 
> The PPS is feed in from pin 1 (DCD) of /dev/cuad1. As I've said, NTP works fine now, after changing "ident" value in PPSGENERIC and recompiling and installing the new kernel. Performance of type 20 driver is good enough for me, thanks for your advice. Maybe I will try that someday.

Probably on FreeBSD you have a more recent version of ntpd and
that would be no better with type 22 driver. Problem I had was
the offset without PPS corresponds to that derived from NMEA
which is 100s of ms out which is then too far for PPS to kick
in. I'm pretty sure this was a known problem that's been fixed
in more recent ntpd. My solution using a large fudge time1 for
NMEA driver along with type 22 driver seems more stable than
with just type 20 driver where I've lost PPS after a couple of
days and had offset shoot up from a few us to 100s of ms with
PPS failing to kick back in.


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