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

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sun Jan 16 07:08:49 UTC 2011


"unruh" <unruh at wormhole.physics.ubc.ca> wrote in message 
news:slrnij3r1n.a4g.unruh at wormhole.physics.ubc.ca...
[]
> Your referent is somewhat unclear.
> If you are saying that your unit is out of spec, then return it.

When operated with earlier firmware, the unit is in spec, but may be out 
of spec with the V3.50 firmware.  Rather than return the unit, I am hoping 
to work with Garmin to produce a better firmware for all users.

> If you are saying something else, I do not know what it is.
> IF the unit operates to spec, then there is enough information to link
> the nmea sentence to its pulse. If it is operating out of spec, then
> there is no reason to even believe that the PPS is actually occuring on
> the turn of the second UTC. A broken device is, I agree, not very useful
> for timekeeping.

When the NMEA data arrives immediately after the PPS signal (within a few 
milliseconds rather than the expected few hundred milliseconds), and when 
that minimum expected delay is not specified, there is an ambiguity as to 
which PPS pulse the NMEA refers.

The aim of my post was to suggest a work-round to that problem for users 
of the reference NTP implementation.

Cheers,
David 




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