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Re: [gpsd-users] Garmin 18X LVC and upcoming week rollover

From: Gary E. Miller
Subject: Re: [gpsd-users] Garmin 18X LVC and upcoming week rollover
Date: Wed, 4 Dec 2019 16:59:11 -0800

Yo Rich!

On Wed, 4 Dec 2019 16:27:25 -0800
Rich Wales <address@hidden> wrote:

> See below for the output from "./gpspipe -R -x 15" (taking care to use
> the "gpspipe" from my latest build).

Common mistake.  Newer clints complaint about verson mismatches.

> I did "./gpsctl -b" about 20 minutes before logging this data.

Sadly you are still in NMEA mode:

> {"class":"DEVICES","devices":[{"class":"DEVICE","path":"/dev/gps0","driver":"NMEA0183"

Sometimes you have to repeat gpsdctl -b, without restarting gpsd, to get
into binary mode.

> $GPRMC,002034,A,3728.0473,N,12212.4437,W,000.0,326.8,200400,015.0,E,D*0C

200400 is 20 April 2000.  Not good.

> $GPGGA,002034,3728.0473,N,12212.4437,W,2,08,1.1,20.9,M,-32.4,M,,*45
> $GPGSA,A,3,03,07,08,09,16,23,27,30,,,,,1.9,1.1,1.5*3B
> $GPGSV,3,1,09,03,17,175,23,07,54,285,40,08,18,126,29,09,80,010,36*72
> $GPGSV,3,2,09,16,28,044,37,23,62,107,40,27,21,090,25,30,24,264,26*76
> $GPGSV,3,3,09,05,03,326,00*41
> $PGRME,3.3,M,7.2,M,7.9,M*25

Pretty much GPRMC, GPGGA, GPGSA and PGRME only.  None have leap seconds.

If you had a sentence with the leap second, then gpsd would look at the
18 current leap seconds and could fix the GPS epoch.

The Garmin $PGRMF reports leap seconds.

Also the Garmin packet 51 (Pid_Pvt_Data) contains the leap second.

With one of those, gpsd can disambiguate the GPS epoch.

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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