[ntp:questions] 1s offset

David Taylor david-taylor at blueyonder.co.uk.invalid
Wed Mar 6 16:05:36 UTC 2013


On 05/03/2013 20:32, folkert wrote:
> Hi,
>
> Something odd is happening.
> I have an old Garmin 18x LVC, a couple of years old and one I bought a
> couple of weeks ago.
> The one from a couple of weeks ago has the most recent firmware.
> The older one only returns one sentence (GPMRC if I remember correctly),
> the new one has factory default settings and returns a couple of them.
> Now when I run either 4.2.6p5 or dev-4.2.7p359, I always get an offset
> of ~1s.
> Both systems are configured to use NMEA + PPS synchronization.
> If I use 4.2.5p158 instead, the synchronization is perfect, on both
> systems.
> As the older garmin has much older firmware and the new garmin the most
> recent one (3.80 iirc), I don't think it is firmware issue. Also I tried
> the new garmin with only 1 nmea sentence but that didn't help.
> The 4.2.5p158 ntp version does not seem to do ipv6? So that is..., a bit
> unfortunate.
>
> Any ideas?
>
>
> Folkert van Heusden

Folkert,

Agreed that it's unlikely to be a firmware issue, but there is an 
interesting graph here:

   http://www.satsignal.eu/ntp/Garmin-GSP18x-LVC-firmware-issue.htm

specifically:

   http://www.satsignal.eu/ntp/Garmin-18x-3.7.png

which shows that the end of the NMEA sentence may be well over 0.5 s 
after the  PPS, and hence into the next second.  Could it be that:

(a) 4.2.5p158 looks for the start of the data, not the end

and:

(b) you haven't specified the appropriate time offset value (fudge 
field) for the serial data for the other two versions of NTP?

Just my initial thoughts.
-- 
Cheers,
David
Web: http://www.satsignal.eu



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