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

[folkert]

> Thanks, Folkert, that's most helpful!  One thing which is unclear to
> me is what do you mean by pin 8?  Is that a programming number, or
> does it refer to the GPIO header?  I did try and find this in the
> RPi documentation, but it's not clear.

Check this picture:
http://jeffskinnerbox.files.wordpress.com/2012/11/raspberry-pi-rev-1-gpio-pin-out1.jpg

GPIO pin 8 is in the upper right block with SPI in it.
GPIO 8 (CE0) is written above it. By the numbering on that diagram it is
physical pin 24.

> I'm currently using NTP driver type 22 on the RPi I would like to
> test with. If I move to the type 28 driver it doesn't matter that
> PPS is left supported in the Linux kernel.  Please confirm there is
> no need to revert to a kernel without PPS support.  Is there a
> simple way of stopping the OS stealing that GPIO pin - turning off
> PPS support with a simple edit?

If I remember correctly, the kernel patch uses GPIO 18 (PCM_CLK), so
using GPIO 8 will work fine with the patched kernel.

> What might matter, of course, is that I would need to move the
> actual PPS signal to a different pin as kernel-PPS and your program
> would not live together, as both would want to grab that pin.  So it
> may mean making a small hardware change as well if I can't turn off
> PPS support.

Maybe, but I'm not an electronics expert (not at all in fact) you can
feed both pins?

> One thing you might want to try is to pulse one of the GPIO pins in
> response to the rising-edge interrupt you get, to see what the delay
> is when measured by a 'scope.

Ok, I've uploaded version 0.2 which can do so.
This version can also, in debug mode, show the offset of the local clock
to the PPS timestamp.


Folkert van Heusden

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