[ntp:questions] garmin 18x and linux

Chris Albertson albertson.chris at gmail.com
Sat Sep 3 01:48:04 UTC 2011

On Fri, Sep 2, 2011 at 12:06 AM, unruh <unruh at wormhole.physics.ubc.ca>wrote:

> No. ntp can use the GPS nmea sentences to time the clock to a few 10s of
> ms. -- you may need to fudge the time offset to make up for the delay of
> the nmea sentence.
Yes, maybe NTP can but not with this Garmin 18 unit.   Some GPSes are better
than others.  And like I said very good units are available for not much
money.  These Garmin units have problems with their NMEA timing.   I tried
to use an even earlier unit and had the same result.   Not worth knocking
your head on a wall when good timing units are available for cheap.

The problem is not just with the timing of the serial data coming out of the
GPS.  There are FIFO buffers in the Serial port in the computer and in the
OS.    PPs is handled by a very low latency interrupt driven interface that
tie stamps the PPS.

Chris Albertson
Redondo Beach, California

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