[ntp:questions] Re: NMEA Driver works only intermittently

rtxo gnu at wraith.sf.ca.us
Tue Sep 9 04:49:45 UTC 2003

Frank Hage wrote:
> I'm a bit stuck with my NTP - NMEA setup under Debian Linux.  The driver
> does work well sometimes, but stops working intermittently. I'm stumped.
> Any help appreciated.

Hi Frank--

> I'm Using a Garmin GPS 16 under Debian Linux 3.0 (2.4.18 kernel)
> ntpp version: ntpd 4.1.2 at 1.892 Tue Aug 26 10:32:03 MDT 2003 (1)

The nmea driver is "atomized" which means you should run a linux
kernel that has had the PPSKit applied. You can find the PPSKit
on kernel.org.

> refclock_gtlin: fd 9 time 3272028642.852101 timecode 60
> $GPRMC,165043,V,4720.5622,N,06041.7866,E,,,080903,008.1,E*61

(stuff deleted)

> $GPGGA,165043,4720.5622,N,06041.7866,E,0,00,,,M,,M,,*56
> nmea: gpsread 55 $GPGGA,165043,4720.5622,N,06041.7866,E,0,00,,,M,,M,,*56
> refclock_gtlin: fd 9 time 3272028643.035334 timecode 28
> $GPGSA,A,1,,,,,,,,,,,,,,,*1E
> nmea: gpsread 28 $GPGSA,A,1,,,,,,,,,,,,,,,*1E
> refclock_gtlin: fd 9 time 3272028643.185247 timecode 68
> $GPGSV,3,3,12,24,26,177,00,26,00,222,00,28,18,109,00,30,00,295,00*79
> nmea: gpsread 68
> $GPGSV,3,3,12,24,26,177,00,26,00,222,00,28,18,109,00,30,00,295,00*79
> refclock_gtlin: fd 9 time 3272028643.218573 timecode 18 $PGRME,,M,,M,,M*00
> nmea: gpsread 18 $PGRME,,M,,M,,M*00
> refclock_gtlin: fd 9 time 3272028643.285215 timecode 27
> $PGRMB,0.0,200,,,,K,,N,W*28

Your garmin is putting out what looks like default sentences.
Check your gps16 docs and turn off every sentence, then turn
on only the $GPGGA and the PPS signal. I've used a gps35 and
done this:

   Turn output off
   turn on just gpgga
   Turn on PPS:

Use the mode 2 flag in the type 20 clock to recognise the $GPGGA
sentence in the ntp.conf file.

These config steps and some hardware hacking let me run a very
acceptable stratum 1 with the gps35. You might check out


...for more details.


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