[time-nuts] Adafruit Ultimate GPS timing message arrival times
Paul
tic-toc at bodosom.net
Mon Aug 1 09:52:18 EDT 2016
On Mon, Aug 1, 2016 at 3:01 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> Depends on your internet connection and/or the specific GPS module you are
> using.
>
> I don't know of any good GPS modules that use NMEA. I do know of really
> crappy internet connections. Bufferbloat is the buzzword.
>
Bufferbloat is an issue but the NTP problem is unknown assymetric delays.
If you're a bit flexible regarding "module" you can do quite well using
NMEA. Both points are shown in the output below (sent using a constant
width font). FURY is a Fury, offset and jitter in milliseconds.
$ ntpq -p
remote refid st t when poll reach delay offset
jitter
==============================================================================
oPPS(0) .GPPS. 0 l 3 8 377 0.000 -0.002
0.003
*GPS_NMEA(0) .FURY. 0 l 2 8 377 0.000 -0.010
0.018
time-d.nist.gov .ACTS. 1 u 264 512 353 105.770 29.742
0.348
+nub .GPPS. 1 s 4 16 377 0.151 -0.025
0.022
Compared to the MTK3xxx in the Adafruit UGPS circa 2-3 years ago.
remote refid st t when poll reach delay offset
jitter
==============================================================================
oPPS(0) .GPPS. 0 l 4 8 377 0.000 0.002
0.004
*GPS_NMEA(0) .ADAU. 0 l 3 8 377 0.000 -78.472
25.623
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