[time-nuts] raspberry pi, adafruit gps & ntp

folkert folkert at vanheusden.com
Sun Jun 16 16:16:04 EDT 2013


Hi,

Ok today my friend Henk (Henk are you still subscribed here?) soldered
the raspberry pi on my adafruit ultimate gps breakout v3. Apart from the
soldering things were totally easy to get to work: only a few tweaks to
cmdline.txt and inittab and the serial data streamed in.
I decided _not_ to patch the kernel after a couple of issues with
missing include files and such. But as only "watching" the nmea stream
gives bad results, I needed to find an alternative for the PPS signal.
So I wrote a little program which watches the GPIO port using poll
(which waits for an interrupt) and then pokes in the shared memory
segment of ntpd.

After 51 minutes of ntpd run-time this gives:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*firewall.intran 192.168.64.2     3 u    7   64  377    0.560   -0.506   0.493
-belle.intranet. 192.168.64.2     3 u   58   64  377    0.560   -0.470   0.405
-time2.intranet. 194.109.20.18    3 u   56   64  377    1.034   -1.282   1.392
+auth1.xs4all.nl 193.67.79.202    2 u   28   64  377   17.580   -0.160   0.490
xSHM(0)          .NMEA.           0 l    1   16  377    0.000  -359.47  10.670
+SHM(1)          .PPS.            0 l    1    8  377    0.000    2.964   0.061

I started the program with statistics logging enabled so I will produce
some nice graphs after a day or so.


Folkert van Heusden

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