[ntp:questions] Re: Garmin gps18: The best DIY gps refclock?

John Pettitt jpp at cloudview.com
Mon Nov 28 17:58:57 UTC 2005


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Roman Mäder wrote:
> Eugen COCA wrote:
> 
> 
>>Any indication about connecting the PPS signal and setting up the ntpd
>>service to work with ?
>>
>>Thank you !
>>
>>P.S. I think the 1 us jitter is true only if using the PPS signal.
> 
> 
> I did configure the PPS device in addition to the NMEA refclock,
> but it does not give me any additional accuracy.
> this "ntpq -p" output is typical:
> 
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> +GPS_NMEA(0)     .GPS.            0 l   25   64  377    0.000   -0.036   0.020
> oPPS(0)          .PPS.            0 l   43   64  377    0.000   -0.046   0.030
> ....
> 
> configured as:
> 
> server 127.127.20.0 mode 2 prefer
> server 127.127.22.0
> fudge 127.127.22.1 flag3 1
> 
> 

The NMEA driver (20) has PPS code built in so you don't need the stand
alone PPS driver (22) - that's why you don't see any difference.  If
you remove the link to pps0 from /dev and restart ntpd you'll see the
non PPS results (not even close to the PPS numbers).

John (also using a GPS18LVC)
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