Buggy WNRO fixup

[Hal Murray]

>> I have a NMEA unit that's off by 1024 weeks.  Somebody
>> is fixing it twice.
> How do you know that?

The time on that system got set to Nov  4  2023

The "twice" part was sloppy, but something strange was going on.

The log message says -4096 weeks which just adds to my confusion.
20 Dec 12:22:32 ntpd[40363]: NMEA(1) Changed GPS epoch warp to -4096 weeks



>> Anybody know where that fixup code is located?  I took a
>> quick scan in the NMEA driver but didn't find it.
> I don't think ntpd adjusts NMEA years.  gpsd does, by looking at the leap
> second. 

The code is in ntpd/ntp_wrapdate.c

refclock_nmea calls it in at least 2 places:

        case NMEA_GPRMC:
                rc_date  = parse_date(&date, &rdata, 9, DATE_1_DDMMYY)
                        && unfold_century(&date, lfpuint(rd_timestamp));

        case NMEA_PGRMF:
                rc_date  = rc_date
                        && gpsfix_century(&date, &gpsw, &up->century_cache);

        rd_reftime = eval_gps_time(refclock_name(peer), &date, &tofs,
                                   (peer->cfg.mode & NMEA_DATETRUST_MASK), 
&up->epoch_warp, &rd_timestamp);


> Can you send this list a few seconds of your NMEA?

$GPRMC,133400.000,A,3726.0851,N,12212.2614,W,0.00,12.81,070502,,,A*4C
$GPGGA,133401.000,3726.0851,N,12212.2614,W,1,5,1.40,38.9,M,-25.7,M,,*5A
$GPGSA,M,3,18,23,10,32,08,,,,,,,,1.68,1.40,0.93*0E
$GPGSV,2,1,08,10,64,019,26,32,64,192,27,23,37,060,16,08,37,293,31*73
$GPGSV,2,2,08,18,23,121,14,24,18,061,,21,17,312,,35,,,*45
$GPRMC,133401.000,A,3726.0851,N,12212.2614,W,0.00,12.81,070502,,,A*4D
$GPGGA,133402.000,3726.0851,N,12212.2614,W,1,5,1.40,38.9,M,-25.7,M,,*59
$GPGSA,M,3,18,23,10,32,08,,,,,,,,1.68,1.40,0.93*0E
$GPGSV,2,1,08,10,64,019,26,32,64,192,27,23,37,060,16,08,37,293,31*73
$GPGSV,2,2,08,18,23,121,14,24,18,061,,21,17,312,,35,,75,24*74
$GPGSV,3,2,10,07,33,250,30,26,25,048,22,06,15,282,16,30,04,243,*7A
$GPGSV,3,3,10,02,01,324,,49,,,*43
$GPRMC,195030.000,A,3726.0713,N,12212.2560,W,0.00,344.40,100502,,,A*75
$GPGGA,195031.000,3726.0713,N,12212.2560,W,1,7,1.15,43.8,M,-25.7,M,,*57
$GPGSA,M,3,26,03,04,06,09,07,16,,,,,,1.45,1.15,0.89*06
$GPGSV,3,1,10,04,70,030,28,16,50,086,26,09,49,314,26,03,48,175,23*73
$GPGSV,3,2,10,07,33,250,30,26,25,048,22,06,15,282,16,30,04,243,*7A
$GPGSV,3,3,10,02,01,324,,49,,,*43
$GPRMC,195031.000,A,3726.0713,N,12212.2560,W,0.00,344.40,100502,,,A*74


-- 
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