Re: PPS fix determination vs. cgps? (fwd)

[Gary E. Miller]

Yo Steve!

On Thu, 21 Jan 2021 13:42:15 -0600
Steve Bourland <sbourland@swri.org> wrote:

> > When in doubt, this tells me a lot about what you did:
> > 
> > # pstree -paul | fgrep gpsd  
> 
> -gpsd,3515,nobody -N -D 3 -n /dev/ttyS0
> 
> (when not wanting to see the output, it is simply ./gpsd -n
> /dev/ttyS0)

Both looks good.

> > No, maybe not long enough.  It can take up to 30 minutes to get the
> > current leap second.  Without that some GPS will not output PPS.  In
> > other cases the receiver reported time may be off up to 18 seconds.
> >  
> 
> So to help my understand...it had been running for over 30 minutes
> prior, and now has run for over 24 hours with the same output.  I
> have an LED on the adapter board that converts the Garmin cable to
> RS-232, driven by the PPS line....and it is blinking away happily.

So, we have now ruled out that common problem.

> > I already asked for the one thing that solves most problems, that
> > tmp.log.  Help me help you, send that.  
> 
> Have started the collection, will attach to this message.

Looks like you are sending GPRMC, GPGSA and GPGSV every cycle.  That
is not normal.  The Garmin, and most other receivers, do not compute
GSV every fix, so sending it every fix is a waste.  Maybe that is
confusing the cycle ender.

BTW, what is your serial port speed?

Can you reset your device to gpsd normal NMEA sentences and see if that
changes anything?  At least try GSV every 5 fixes, not every one.

> > Correct.  But, as you said, xgps and xgps are working as you
> > expect, so no point looking at the working part.  
> 
> My thinking was to see why they thought they had a good fix (what
> they were keying off of)

That is right there in the log you sent:

gpsd:IO: <= GPS: $GPGSA,A,3,01,26,,31,32,,,,,,,,1.9,1.7,0.9*33
gpsd:PROG: NMEA0183: xxGSA sets mode 3

> to see if PPS was looking for a different
> key...

Nope.  Same thing, the mode byte.  You see it in include/gps.h as
gps_fix_t -> mode.  The issue here is always WHEN, not WHERE.  Nothing
is the "same time" in gpsd.

> again, my lack of
> understanding of the systems involved.

No one understands all this.

> > The FULL and COMPLETE debug log.  
> 
> Just to try and help keep your life a bit simpler, original command
> that generated the above PPS log message:
> -gpsd,3515,nobody -N -D 3 -n /dev/ttyS0

Everyone thinks that, almmost never true.

> Log attached with hopefully enough seconds of runtime (file size
> limits) called with:
> # gpsd -nND 6 /dev/ttyS0 >& tmp.log

Yes, good enough.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  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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