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

[Alexander Carver]

On 10/24/2011 11:21, Gary E. Miller wrote:
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> Yo Alexander!
>
> On Sat, 22 Oct 2011, Alexander Carver wrote:
>
> > Does anyone have an idea why the time reported to ntpd from gpsd (via SHM(0) )
> > would suddenly be off by more than half a second?
>
> 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.