[ntp:questions] Re: NMEA and PPS

John Pettitt jpp at cloudview.com
Mon Jul 10 01:20:28 UTC 2006

DJ wrote:
> Hi
> the rtfm is confusing on  the subject of NMEA and PPS. I have an
> external RS-232 GPS rx with NMEA output feeding /dev/gps0 and
> in ntp.conf (on intel/linux platform). With the correct
> use of fudge time1 I can get my ntpd to act as a stratum 0 server and
> will track pool ntp servers to within 100ms drift . I wish to improve
> the precision/accuracy and would like to use the PPS kernel/drivers. Is
> this possible with a simple NMEA device i.e. does the PPS kernel patch
> give a better stability or do I need a PPS gps clock ?

It all depends if your gps has a pps output - rtfm(receiver) - some (like the gps 18lvc do, others
like the gps18serial don't).   Having pps is independent of being an NMEA device (both of the
examples above are NMEA).

If you do have pps on your gps then you need to figure out how to get it to ntp and that will
involve ether a kernel rebuild (FreeBSD) or the user space pps code (Linux 2.6) or ppskit (linux
2.4) google for your os and pps will normaly yield info.


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