[time-nuts] GPS 18x PC/LVC 3.90 (August 28, 2013)

[Kiwi Geoff]

David J Taylor  wrote:
> GPS 18x PC/LVC 3.90 (August 28, 2013)
> Folks, I have received notice of an update to the GPS 18x LVC firmware,
> which can be downloaded here:
>     http://www8.garmin.com/support/agree.jsp?id=4055
> ...
> Any reports would, I'm sure, be welcome.

Thanks for the firmware upgrade pointer David.

Folks may remember that the 18x had some terrible issues with "serial
latency" in earlier versions, where the serial NMEA could complete in
the following second epoch. Sometimes you had the right UTC time, and
sometimes you didn't.

I recently made a 24 hour log of the Garmin 18x sitting in exactly the
same location that was used to create the graph (thanks to Hal Murray)
on your page David:

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

but using the new version 3.90

Here is a quick comparison between version 3.70 and the (new) 3.90 firmware.

The following times are the delay of the serial data with respect
leading edge of the 1PPS.

Measured every second for 24 hours, thus 86,400 samples

330ms Ver 3.70 Minimum delay of RMC first character
504ms Ver 3.70 Maximum delay of RMC first character
174ms  Ver 3.70 delta (Max - Min) RMC first character over 24 hr period

336ms Ver 3.90 Minimum delay of RMC first character
517ms Ver 3.90 Maximum delay of RMC first character
181ms  Ver 3.90 delta (Max - Min) RMC first character over 24 hr period

David, the new (3.90) version has a similar latency to version 3.70
and thankfully not back to the bad old days of crossing second epoch
boundaries !

And finally,  to go off "time nuts" topic (but just briefly ;-):

David, if you are like me and are fascinated with algorithms, here is
a wonderful bit of history that has just been brought back to life. A
working emulator of Clive Sinclair's Scientific Calculator, and how
they took a four function calculator chip from Texas Instruments and
in 320 words made the worlds first single chip Scientific Calculator.

It did not have the accuracy of the HP35's Cordic algorithms, but
still amazing - enjoy some UK history:

http://righto.com/sinclair

Regards, Kiwi Geoff (Christchurch, New Zealand).