[ntp:questions] ntpd + GPS + PPS + Linux (Ubuntu Lucid)

Stephan Skrodzki skrodzki at stevekist.de
Wed Jun 1 13:58:45 UTC 2011

Hi there,

I am trying since some time to attach a SkyTraq Based GPS receiver to a
serial port + pps which "basically" works fine by using gpsd 2.92 and
ntpd 4.2.4p8.

Still I get "time resets" every some hours which I do not really
understand: i get less time resets (+1 sec ... -1 sec) when I configure
only pps via shm. Configuring gps + pps via shm even gets worse...

Ok, not to bother you with support requests on old version, I will go
for the actual release and therefore I have a few questions:

a) can I use PPS there without the PPSAPI? I do not really want to build
a new kernel... having a short look it seems that there is no PPS
support for the SHM interface (anymore?)?

b) could somebody hint me to a working ntp.conf for nmea gps + pps and
no external ntp servers?

c) I did convince somebody at SkyTraq to provide me also a special NMEA
sentence for discovering leap seconds, AFAIS I have to modifiy
refclock_nmea.c in the same way as done for the GARMIN devices...

Sorry if my questions are not precise enough but some answers could make
me save a lot of work :-)

Thanks & Br

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