[ntp:questions] Problem troubleshooting gps/pps on freebsd 8.1

Dave Hart hart at ntp.org
Thu Dec 16 05:15:54 UTC 2010

On Thu, Dec 16, 2010 at 04:02 AM, Peter S <pst at telia.com> wrote:
> The gps is connected to the serial port and the pps signal to dcd. I
> run ntpd 4.2.6p2 and freebsd 8.1.
> I can simply not get the nmea reference clock to work and I don't know
> how to troubleshoot it.
> Running ntpd -d I see this so I guess ntpd sees the gps:
> nmea: gpsread 70 $GPRMC,033730,A,5926.7899,N,01758.1371,E,
> 000.3,339.3,161210,004.0,E*72
> nmea: gpsread 66 $GPGGA,033730,5926.7899,N,01758.1371,E,
> 1,05,2.4,32.4,M,23.3,M,,*7A

You may be suffering from a refclock_nmea bug where multiple sentences
were processed including stuffing an offset in the clock filter, when
only one should go that far.  Either configure the GPS to send only
one of GPRMC or GPGGA (both of which ntpd understands) or refer to
html/driver/driver20.html for the mode to use in ntp.conf to instruct
it to process only one or the other of the sentences you're seeing
each second.

I mention last because so few seem willing to upgrade ntpd when a
workaround will do, you could also upgrade to 4.2.6p3-RC11 or a recent
ntp-dev (4.2.7) which have this NMEA bug fixed.

Dave Hart

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