[time-nuts] Garmin 18x GPS WNRO, revisited

[Fiorenzo Cattaneo]

The Garmin 18x I have still works, and I verified it works after a power
cycle. I'm running firmware version 4.40.

Apparently all the 4.XX firmware versions are related to GPS week rollover
fixes. Earlier versions also have fixes for "improved" time keeping. Here
is the download link for 18X:

https://www8.garmin.com/support/download_details.jsp?id=4055

These are all the downloads for the 18x, including the Garmin tool
SNSRXCFG:

https://www8.garmin.com/support/collection.jsp?product=010-00321-31


This link from David might also be of interest:

https://www.satsignal.eu/ntp/Garmin-GSP18x-LVC-firmware-issue.htm


I've found the upgrade process to be a bit complicated, the upgrade
instructions didn't work for me. So this is what I did:
* set receiver at 9600 baud, power cycle
* with garmin utility, set receiver in garmin mode, power cycle
* run upgrade utility, power cycle,
After the upgrade I couldn't get the receiver back to NMEA mode, so I just
did it programmatically:

/* fd is the file descriptor pointing to the open file to the tty device
in RAW mode @ 9600 baud */
/* send_byte is a wrapper code to write() which handles timeouts and write
errors */
void garmin_set_nmea(int fd)
{
        printf("==> garmin_set_nmea\n");
        /*
         * garmin binary command to switch to NMEA output
         */
        int i;
        unsigned char buffer[] = { 0x10, 0x0A, 0x02, 0x26, 0x00, 0xCE,
0x10, 0x03 };
        for (i = 0; i < sizeof (buffer); i++)
                send_byte(fd, buffer[i]);
}


-- Fio Cattaneo

Universal AC, can Entropy be reversed? -- "THERE IS AS YET INSUFFICIENT
DATA FOR A MEANINGFUL ANSWER."

-----Original Message-----
From: time-nuts <time-nuts-bounces at lists.febo.com> On Behalf Of David J
Taylor via time-nuts
Sent: Friday, 29 November, 2019 10:28
To: Discussion of precise time and frequency measurement
<time-nuts at lists.febo.com>
Cc: David J Taylor <david-taylor at blueyonder.co.uk>
Subject: Re: [time-nuts] Garmin 18x GPS WNRO, revisited

From: Rich Wales

I may have found the answer to my own question.

I added "time1 619315200" to the "refclock" line in my ntp.conf file, and
restarted ntpsec, and it appears to be sane once again.

(And, of course, 619315200 = 7,168 days = 1,024 weeks.)

Rich Wales
richw at richw.org
====================================

Thanks for reporting that, Rich.  I haven't seen that issue with either
the
GPS18 LVC, or the GPS18x LVC, but neither have been powered down.  Were
yours running continually?  Anyway, I love the fix!

I'm running reference NTP here, and noted that with a type 22 PPS driver,
the "prefer" must include the type 20 NMEA driver.  With the problem
pending, I had hoped that using an e.g. Internet source for coarse time
might have been enough, and had commented out the NMEA source, but it
appears not to be the case.  The PPS was never used (but it appeared in
the billboard).

Cheers,
David
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk
Twitter: @gm8arv


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