[ntp:questions] GPX18x LVC 3.50 firmware - high serial delay problem workround

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sat Jan 15 06:50:34 UTC 2011


"unruh" <unruh at wormhole.physics.ubc.ca> wrote in message 
news:slrnij219b.cr7.unruh at wormhole.physics.ubc.ca...
[]
> The shmslp driver does something similar. It uses some other source to
> get the seconds right and then hands over to the PPS to get the
> nanoseconds right. But it uses only the PPS pulse, not the serial nmea
> data. It thus requires you to have another source of time. However with
> something like the GPS18 it delivers both the nanoseconds via that PPS
> AND the seconds via the nmea sentence. Of course that only works if you
> know which second that PPS pulse refers to. The specs of the GPS18 say
> that it is the previous pulse that that nmea timestamp refers to . But
> if it takes 2 sec say to deliver the nmea sentence, then the "previous"
> pps pulse is the wrong one. So the sentence MUST start less than 1 sec
> after the pulse. If it does not, it is broken and is not working
> according to spec. I have never had trouble with teh GPS18, but they are
> refering to the GPS 18x, the newer version.

Yes, it's the GPS 18x LVC - the newer version - and even then the problem 
only happens with newer versions of its firmware.  This has been reported 
to Garmin.

Cheers,
David
 




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