[ntp:questions] Re: Garmin GPS 18 firmware update -> 200ms offset

Patrick Klos pklos at osmium.mv.net
Tue Nov 29 17:26:09 UTC 2005


In article <438c54e5$0$17246$4d4ef98e at read.news.ch.uu.net>,
Roman =?ISO-8859-1?Q?M=E4der?=  <newsXXF.10.rmaeder at spamgourmet.com> wrote:
>Patrick Klos wrote:
>> .... Keep in mind that there is no relationship between the PPS and the
>> time that the NMEA strings are sent over the (async) serial line except
>> that the NMEA
>> messages are EXPECTED to come out BEFORE the next PPS.  Of course, that's
>> not
>> always the case, but that's a different issue.  (we've seen NMEA strings
>> for one second not show up until AFTER the following PPS causing all kinds
>> of confusion!)
>
>for the Garmin GPS 18 it's the other way around: the pps pulse precedes the
>first NMEA sentence output for that second. As far as I can tell the start
>of the sentence is aligned perfectly with the pulse.

I'm sure you can't rely on the NMEA strings coming out with any specific
relationship to the pulse.  We've seen Garmin GPS's get very busy inside
and skew the NMEA strings all over the place, including after the NEXT PPS.

================= GPS based time synchronization solutions =================
    Patrick Klos                           Email: patrick at timegeeks.com
    Klos Technologies, Inc.                Web:   http://www.timegeeks.com/
==================== http://www.loving-long-island.com/ ====================




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