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

folkert folkert at vanheusden.com
Mon Jun 17 14:37:55 UTC 2013


David,

> Fine, Folkert.  The GPIO pins are numbered in your program exactly
> as I would expect, and the diagram just confirms that.  Yes, the
> patched kernel can remain, and PPS operation should be unaffected.
> I was able to drive the two pins (GPIO 18 and GPIO 8) in parallel,
> and I have a signal level of about 2.5 V from a resistive divider.
> I'm actually driving it from a Trimble SMT module where the serial
> is over the USB, and gpsd see the GPS data perfectly.

Ah!
Is the serial over usb working stable on your rpi?
I have lots of problems with usb devices dropping from the usb bus. Also
with a powered hub.

> Thanks for the monitoring output.  The tie delay between the PPS
> leading edge and the change of the monitoring line varies between
> 270 to 390 microseconds, so despite the jitter being reported in the
> 3-5 microsecond range, the "internal clock" is perhaps running about
> 1/3 millisecond behind "real" time.  You will be able to see the
> performance compared to kernel-PPS here:
> 
>  http://www.satsignal.eu/mrtg/performance_raspi-2.php

cool!

> and a comparison with other stratum-1 Raspberry Pi cards here:
> 
>  http://www.satsignal.eu/mrtg/performance_ntp.php
> 
> The software compiled and installed without any issues.  I've yet to
> figure out how to get it to auto-start - you might like to add that
> to your instructions.  I may add a section to my Web page with a
> step-by-step guide, as this is so much easier than have to use a
> non-standard kernel.

Will do.

For now:

edit /etc/rc.local and add the following (BEFORE the exit 0 statement
and AFTER the #!/bin/sh line):

/usr/local/rpi_gpio_ntp -N 1 -g 8

(replace '8' by the gpio pin)


Folkert van Heusden

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