[time-nuts] raspberry pi, pps & interrupts by kernel

folkert folkert at vanheusden.com
Sat Dec 13 20:47:16 EST 2014


Years(?) ago I wrote a program rpi_gpio_ntpd to be able to use a pps
with a raspberry pi (or any other linux system with standard gpio pin
support) and ntp. Works fine altough the jitter is between 0 and 15us.

By accident I read https://github.com/raspberrypi/linux/issues/109
where it is written that the standard(?) image (the one installed with
the "rpi_update" script) now includes kernel gpio pps support!
I've installed that kernel and indeed, there now is a
/sys/module/bcm2708/parameters/pps_gpio_pin "file" to which you "echo"
the pin number on which you feed the pps signal.

I tested it...and could not get it to work. gpsd opens pps0 but strace
does not show me the regular ppsapi syscalls and also ppstest gives a
time out.
I'm probably missing something trivial here but if any other of you
would like to give it a try please let me know (here) if and how you

Folkert van Heusden

Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com

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