"unruh" <un...@wormhole.physics.ubc.ca> wrote in message
news:slrnij219b.cr7.un...@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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