Added support to reserve/enable a GPIO pin to be used from pps-gpio module

[tjko]

This change enables use of existing pps-gpio module with Raspberry Pi. This change should be "no-op", as it is disabled by default. It adds two kernel cmdline options:

bcm2708.pps_gpio_enable
bcm2708.pps_gpio_pin

When user wants to use pps-gpio module they need to add "bcm2708.pps_gpio_enable=1" into cmdline.txt, this will enable PPS on GPIO 18. If any other GPIO pin is desired it can be selected using the second option...

After system is booted with this option, pps-gpio module can simply be loaded and it will find the designated GPIO pin as a PPS source:

[   61.691271] pps_core: LinuxPPS API ver. 1 registered
[   61.691305] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <[email protected]>
[   61.700274] pps pps0: new PPS source pps-gpio.-1
[   61.700357] pps pps0: Registered IRQ 188 as PPS source

This change is based on the patch by Hauke Lampe: https://github.com/lampeh/rpi-misc/blob/master/linux-pps/linux-rpi-pps-gpio-bcm2708.diff

[popcornmix]

I think GPIO18 is a bad choice for a B+ board (it collides with I2S used by audio cards).

Can you remove pps_gpio_enable, initialise pps_gpio_pin to -1, and use bcm2708.pps_gpio_pin= as the way of enabling this (for any non-negative pin number).

[tjko]

That's a good idea, no really need for two kernel options.

Can I also include change to enable PPS modules in bcmrpi_defconfig? PPS modules add only about 52KB to /lib/modules

[tjko]

Patch has now been cleaned up, and uses just single new kernel/module option:
bcm2708.pps_gpio_pin=n

It shouldn't really change anything until user manually enables desired GPIO pin to be used as PPS source with pps-gpio kernel module.

I added info message when this option is used (nothing is printed if option is not specified), so its easier for users to confirm that the option they passed actually took effect (and that the option is supported in kernel that they use):

...
[    0.029535] bcm2708: GPIO 18 setup as pps-gpio device
...
[   26.587907] pps_core: LinuxPPS API ver. 1 registered
[   26.587937] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <[email protected]>
[   26.605937] pps pps0: new PPS source pps-gpio.18
[   26.606019] pps pps0: Registered IRQ 188 as PPS source
...

Also the device ID in the device tree gets populated with the GPIO pin number, making it bit clearer which /dev/ppsX device maps to which PPS source...

[kukabu]

It would be good!
CONFIG_PPS=m
CONFIG_PPS_CLIENT_LDISC=m
CONFIG_PPS_CLIENT_GPIO=m

[popcornmix]

Can you squash first two commits (git rebase -i HEAD~3 and following instructions, then git push -f).

[tjko]

Everything is now in as single commit. This should make using GPS as PPS source with Raspberry Pi rather easy, when it comes to kernel...

[jera-sea]

I am getting a timeout when using ppstest on /dev/pps0
the debug messages say "time format unspecified".
It is a copy of the latest raspbian image with the kernel recompiled and pps gpio added as modules.

[tjko]

It seems gpsd / ntpd can sometimes auto-load pps_ldisc module (that can
be used for PPS source on COM port using some of the signal lines ;
CTS etc...), this won't work on serial ports that don't implement
those lines like ttyAMA0 on RPi...
So on RPi you could see things like:

[   26.246266] pps_ldisc: PPS line discipline registered
[   26.248015] pps pps0: new PPS source ttyAMA0
[   26.248292] pps pps0: source "/dev/ttyAMA0" added

If that happens then likely pps_gpio was loaded after pps_ldisc
module, and created "pps1" (/dev/pps1") and you would need to use that
for PPS, instead...

If thats not it, then you may want to check that kernel got the command line parameter (bcm2708.pps_gpio_pin) specifying which GPIO pin to use:

[    0.029902] bcm2708: GPIO 18 setup as pps-gpio device

If you don't see message similar to one above, then loading pps_gpio wont work.
But if message similar to the one above shows up, then you should see pps_gpio generate messages like this:

[   78.339732] pps pps0: new PPS source pps-gpio.18
[   78.339813] pps pps0: Registered IRQ 188 as PPS source

Note which ppsX device was assigned, since it might not always be "pps0"...

(above assumes that you set pin 18 using command line option to
kernel: bcm2708.pps_gpio_pin=18)

Btw, have you checked the instructions at: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#easy

[jera-sea]

Oh god...
Sorry for wasting your time.

the ribbon cable was dodgy.

facepalm