[time-nuts] My Garmin 18x, Ver 3.50, currently 1 second slow to UTC
geoff36 at gmail.com
Wed Jan 5 11:08:38 UTC 2011
Hal Murray wrote:
> It would be really neat if you could run similar experiments on 3.3 and/or
I have run some more tests Hal, with V3.5, averaging ON and OFF.
I include V3.2 for comparison.
I measured the time of the "START" character ($) of the $GPRMC
sentence and the "LAST" 0x10 (Linefeed) character, relative to the
leading transition of the 1PPS, GPS 18x set to 4800 Baud.
Version 3.20 firmware for Garmin 18x
START Min = 370
START Avg = 433 (N = 7200)
START Max = 518
LAST Min = 519
LAST Avg = 582 (N = 7200)
LAST Max = 667
Version 3.50 firmware for Garmin 18x with Averaging ON
START Min = 768
START Avg = 813 (N = 4194)
START Max = 871
LAST Min = 917
LAST Avg = 962 (N = 4194)
LAST Max = 1020 ( 7 sentences finished over 1,000 ms)
Version 3.50 firmware for Garmin 18x with Averaging OFF
START Min = 769
START Avg = 805 (N = 3563)
START Max = 858
LAST Min = 918
LAST Avg = 954 (N = 3563)
LAST Max = 1007 ( 4 sentences finished over 1,000 ms)
This agrees with what Kasper Pedersen wrote earlier:
> 3.10 starts transmitting 350ms .. 480ms after PPS
> 3.30 starts transmitting 920ms .. 1220ms (!) after PPS
> 3.50 starts transmitting 700ms .. 1220ms (!) after PPS
The "averaging" appears to have about an 8 ms penalty in delaying the
NMEA data stream.
We can see in the above, that V3.5 RMC is infrequently not finishing
"within" the correct second !
For "my" application I need both RMC and GGA to finish within the
current second - which the Garmin 18x does very comfortably with
version 3.2 and under.
Kevin Rosenberg wrote:
> Has anyone had trouble with reverting firmware upgrades on
> Garmin products? Of course, feedback on going back from
> 3.50 to 3.20 on an 18x would be most specific to my situation.
I have "reverted" quite a number of times now Kevin - trying to
understand why the 18x can be 1 second slow. I have never had an issue
putting in an older version into the 18x, the updater software does
know what your doing, it says:
"Your current software version is newer than the update version.
Do you want to replace your current software version with an older version ? "
We click the YES box.
To do the above timing tests I had v3.5 loaded into my 18x, I then
reverted to v3.2 and everything worked fine Kevin (to answer your
Regards, Kiwi Geoff (New Zealand).
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