[gpsd-dev] New 0.5 draft of the SemPiTernal HOWTO

[Frank Nicholas]

> On May 5, 2016, at 8:07 PM, Gary E. Miller <gem at rellim.com> wrote:
> 
> Yo Frank!
> 
> On Thu, 5 May 2016 19:49:28 -0400
> Frank Nicholas <frank at nicholasfamilycentral.com> wrote:
> 
>> We want to use PGGA sentence because it appears first, closest to
>> the start of the second in each cycle.
>> 
>> You have mode set to 17, using message GPRMC.  Can someone who knows
>> more than me, explain to me if it really matters?
> 
> 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...

> 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.

Thanks,
Frank
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