[ntp:questions] garmin 18x and linux

unruh unruh at wormhole.physics.ubc.ca
Mon Sep 5 16:47:20 UTC 2011

On 2011-09-05, Miroslav Lichvar <mlichvar at redhat.com> wrote:
> On Mon, Sep 05, 2011 at 03:04:54PM +0000, unruh wrote:
>> On 2011-09-05, Miroslav Lichvar <mlichvar at redhat.com> wrote:
>> > With 18x LVC (firmware 3.70) I see errors up to 150 ms. That
>> > wouldn't be that bad if it was randomly distributed.
>> >
>> > A capture over 30 hours:
>> > http://mlichvar.fedorapeople.org/tmp/18x_nmea.png
>> This was captured how? Is that the beginning or the end of the nmea
>> sentence?
>> You have some where the offset is negative. Does this really mean that
>> the nmea came in before the beginning of the second it referred to?
> No, I forgot to mention that was already with 0.5s correction applied.
> It's from gpsd which seems to make the NMEA receive timestamp after
> the message is processed.
Never did understand that. Timestamping the beginning of the sentences
is cheap enough and easy enough. 
Mind you, your fluctuations are far more than I would expect simply from 
variations in the length of the sentences.
Are there more sentences delivered than just the one gpsd uses?

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