Re: [gpsd-users] Sudden shift in time?

[Gary E. Miller]

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Yo Alexander

On Mon, 24 Oct 2011, Alexander Carver wrote:

> > Yup.  SHM(0) time is taken from the serial stream coming out of the GPS
> > as was never designed to be more accurate than 1Sec.  Just check out the
> > NMEA stream from a GPS on the console.  You can see it varies all over the
> > place.
>
> Well, not NMEA but SiRF in my case.  Anyway, I can understand variance but I
> didn't expect to go from an offset of 20ms to 660ms in one read. That's what's
> got me surprised, the jitter is actually reasonably low normally but this was
> just way off the charts then went back to normal.  First time I had ever
> actually seen it.  All the logs show that the time stamp is normally staying
> within 50ms of the clock so I was even more confused by the very sudden shift.

You may not have expected it, but there it is anyway.

Same applies to all the binary GPS outputs.  That little CPU in the
GPS sometimes has a lot of work to do before it can output a fix and
they make no attempt to compensate for the extra CPU load in the output.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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