Yo Frank! On Thu, 5 May 2016 20:13:53 -0400 Frank Nicholas <fr...@nicholasfamilycentral.com> wrote:
> > NMEA sentences are vaiable length. So you want to use the first one
> > to cut jitter on the NMEA time. In practice you have the PPS,
> > 10,000 times more accurate, so never a problem unless you lose
> > PPS.
>
> And on the Adafruit HAT & Ultimate GPS breakout board, the first NMEA
> sentence at the start of a cycle is “GPGGA”. So are you saying that
> with PPS, it really doesn’t matter? Your second sentence makes me
> think it matters. The last sentence makes me think it **doesn’t**
> matter...
It does not matter, up to a point.
If you lose PPS, your ntpd may fall back to NMEA time, if the fudge is
off that makes things jumpy.
Your ntpd may lock onto NMEA time instead of PPS time and now you could
be way off. This can happen at startup.
As some point, you NMEA time os so far off that the PPS is not paired
to the proper second.
> > Some GPS can barely get all their sentences out every second at
> > 9600. If you have a lot of sats in view, or optional NMEA turned
> > on, your buffers may overflow.
>
> On the above GPS, there are periodic (not every second) sentences
> that will cause a cycle to extend beyond one (1) second at 9600.
Yup, not good.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com Tel:+1 541 382 8588
pgp7dkwGHNXUU.pgp
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