[ntp:questions] pps breaks when nmea is enabled for ntpd

David Lord snews at lordynet.org
Sat Jun 15 15:54:07 UTC 2013

Richard Cagley wrote:
> I have a TI DM8168 processor and a u-blox gps.
> If I enable an internet server and pps, then pps works great
> server clock.redhat.com iburst prefer minpoll 4 maxpoll 4
> server minpoll 4 maxpoll 4
> fudge flag3 1
> However, if I add an NMEA server to my ntp.conf file like this
> server mode 1
> fudge flag1 1
> server minpoll 4 maxpoll 4
> fudge flag3 1
> then pps stops working. I can kill ntpd and ppstest no longer works. It's
> as though nmea is clobbering the serial port.
> It sorta feels like this, but there was no resolution
> http://lists.ntp.org/pipermail/questions/2011-September/030347.html
> Can anyone help me. I've really been struggling with this.

I'm using NetBSD-6.1 ntpd 4.2.6p5 but have also had pps + nmea
working on ubuntu.

You probably need to determine then add time2 0.xyz sec to
your config. The time2 value is for your particular gps and
gps firmware version.

For my "Sure" gps I have:

server mode 18 prefer
fudge stratum 4 time2 0.417 flag1 0 refid GPSb
fudge flag2 0 flag3 1 refid PPSb

 From peer summary I have: mean=0.000 rms=0.004 max=0.038

The 0.038 is mostly due to load from two cron jobs each evening.


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