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Re: [gpsd-dev] ✘reset "Support UBX NAV-PVT" commit 22a020ec1c2bc85eff68

From: Gary E. Miller
Subject: Re: [gpsd-dev] ✘reset "Support UBX NAV-PVT" commit 22a020ec1c2bc85eff681ecacc6d2bb79fdddc9c
Date: Wed, 6 Sep 2017 12:53:09 -0700

Yo Hal!

On Wed, 06 Sep 2017 00:53:38 -0700
Hal Murray <address@hidden> wrote:

> address@hidden said:
> > One you do add it up, you'll see that it just does not fit in the
> > time allotted.   
> I did add it up.  It does fit.

Then we are using math from alternat universes.

> Let me try again.  There are 5 types of sentences.  Each second has 1
> each except for GPGSV which has 3.  So there are 7 sentences each
> second.  Back of envelope.  7 sentences times 100 bytes per sentence
> times 10 bits per byte. That 7000 bits, well below 9600.  (The 100
> bytes/sentence is way high.)

You are fogetting many terms.  The delay from PPS to the first sentence,
the delay between each sentence, the length variation in sentences, the
USB queueing time.

But even 7,000 is WAY too close for 9.600 to actually fit, given the
sentence length variations, etc.  I would never want to run
closer then 2x.

Believe your data, your data is telling you it does not work.

> > Well, without a time frame not useful.  
> I sent a typical sample a few messages ago.

And as I said already, your 'typical' is OK, It is the occasioanl worst
case that causes your failure.  Stop worrying about typical.

Let's not go around this loop yet again.

> It had time stamps.
> Would you like more?

No, I've seen enough, clearly your speed is too slow.

> PPS pulse is 4 ms wide.


> Serial port is active for about 1/2 second, idle for the other half.

Not good, but insufficient data.  And does not match up with your
calculations above.

> The serial stuff starts about the same time as the PPS.  Sometimes
> it's a few ms before the PPS.  Earliest I've seen is 7 ms before PPS.

If it is before the PPS then that is a real problem.  A show stopper
problem.  The PPS MUST be at the top of the second.  The NMEA MUST NOT
start before the top of the second.

If your NMEA is reporting the new second, before it happens, then of
course things will fail.  It is flat wrong about the time.

And I'm gonna bet you have still not tried: gpsctl -s 19200

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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