After I sent this message, I did some research and found the
following blurb from the ntp.org archives. Looks like 18x is
behaving as expected. Ugh.... Might be easier just to buy
an 18 LVC than mess with this 18x.
URL: http://support.ntp.org/bin/view/Support/ConfiguringGarminRefclocks
6.1.4.2. GPS18x-LVC specifics
Please note that the GPS18x-LVC sometimes gives odd huge offsets in the
range of -600ms upto -700ms. One specific model was examined a bit closer
and showed a varying delay between the asserting edge of the PPS signal
and the receive time of the $GPRMC sentence of 580ms to 610ms at 4800bd.
(Only $GPRMC was enabled in the GPS18x and the NMEA driver, though
according to the GPS18x spec $GPRMC should be the first sentence in a
burst anyway if enabled in the receiver. See section 4.2 of Garmin's
GPS18x tech spec.) Using a fudge time2 of 0.600 was needed to avoid
malfunction of the NMEA clock driver. I (mailto:[email protected]) do not
know if this affects all GPS18x-LVC models or if this is baud rate
dependent. (Apart from the transmission duration itself, which is of
course baud rate dependent per se and should account for ~150ms for a
$GPRMC at 4800bd.)
If you experience severe trouble with the GPS18x-LVC a possible solution
is to configure a few good public NTP servers as reference and configure
the NMEA driver as a 'noselect' peer with PPS disabled and a fudge time2
of 0.0. When the system becomes stable, use the negated offset given for
the NMEA driver as fudge time2, remove the 'noselect' from the clock
driver and enable PPS processing with fudge flag1.
It seems that using the GPS18x-LVC without PPS support and some basic
calibration cannot be recommended.
On Mon, February 28, 2011 1:24 pm, Alby wrote:
>
>
> David:
>
>
> Well, it appears I do have an 18x (GPS 18x LVC, 5m). I'm running this
> on a Debian OS (Version 2.6.26.pps001). As for the type 28, I was just
> following the ntp.conf specs from:
>
> URL: http://time.qnan.org/#results
>
>
>
> Got any suggestions to correct this 18x device and a recommended
> server/fudge config setting?
>
> Thanks,
>
>
_______________________________________________
pool mailing list
[email protected]
http://lists.ntp.org/listinfo/pool
