[ntp:questions] Odd offset for PPS DCD w/ Garmin GPS 18x LVC

David J Taylor david-taylor at blueyonder.co.uk.invalid
Tue Mar 22 17:21:31 UTC 2011


"lellis" <larry.ellis at gmail.com> wrote in message 
news:efc6e755-c213-4a10-90f9-420384001da3 at s18g2000prg.googlegroups.com...
> On Win XP, I am seeing an odd positive offset of about 128ms on the
> Atom driver, relative to other sources:
>
>
>     remote           refid      st t when poll reach   delay
> offset  jitter
> ==============================================================================
> *GPS_NMEA(1)     .GPS.            0 l    6   16  377    0.000
> 0.373   0.919
> xPPS(1)          .PPS.            0 l    5   16  377    0.000
> 125.447   0.830
> -clock.team-cymr 172.16.65.22     2 u   39   64   77   12.989
> -41.044  44.960
> +ntp.okstate.edu .USNO.           1 u   42   64   77   28.906
> -18.762  25.784
> +navobs1.wustl.e .GPS.            1 u   38   64   77   19.133
> 1.819  19.599
>
> Normally, I just use NMEA with fudge, but that was also showing the
> odd offset so I removed fudge and added the Atom driver to help debug
> this.
>
> (Normally the status shows oPPS(1) but xPPS(1) is seen above for the
> obvious reason.
>
> ntpd is Dave Hart release 4.2.7p138;  I have a serialpps-ppsapi-
> provider.dll dated 6/6/2009.
>
> Any ideas or recommendations.

Larry,

You may want to revert to the 3.20 firmware for you GPS 18x LVC - see what 
others have written:

  http://support.ntp.org/bin/view/Support/ConfiguringNMEARefclocks#Section_6.1.12.2.

  http://support.ntp.org/bin/view/Support/ConfiguringGarminRefclocks

and there is a somewhat flawed analysis here:

  http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm#gps-18x

(flawed in that I was being helped by a UNIX person, and the Windows 
driver does not work in exactly the same way as we had assumed).

Cheers,
David 




More information about the questions mailing list