PPS input on a generic GPIO pin on Raspberry Pi.

Peter Ankerstål peter at pean.org
Tue Mar 22 21:09:38 UTC 2016

> On 05 Mar 2016, at 07:54, Peter Ankerstål <peter at pean.org> wrote:
>>> GPIO is supported on the Pi, I'm using it on 11-Current on my home
>>> control software to drive relays on my pool hardware (e.g. valves,
>>> heater, VFD motor drive, etc) and it is working very well.  I don't
>>> believe tapping into that at the kernel level to expose a pps signal
>>> (e.g. on /dev/pps or something of the like) would be very difficult
>>> at
>>> all, since the low-level driver capability is already present.
>>> If I get some free time I'll dig around a bit and see if I can cobble
>>> something up.  It's of some interest to me as well since I have a GPS
>>> clock here that currently talks to a serial port on an Intel-based
>>> machine and being able to move that to a $35 "appliance" for NTP
>>> using
>>> the Adafruit setup looks sort of attractive given that the Pi plus
>>> the
>>> module would be under $100 all-in.
>> Don't "cobble something up" just yet... there is "a right way" to fix
>> this, which is a generic gpio-pps driver.  The problem is that it
>> requires support from the new INTRNG, and the rpi hasn't been converted
>> to that yet.  I'm checking around to see if someone has done the
>> conversion for rpi and it just hasn't been reveiwed/committed yet; if
>> not, I guess I'll try to do it myself.
>> Writing the actual gpio-pps driver will be pretty quick and easy once
>> we have the intrng support, I think it'll take me a couple hours.
Any new here? Would be really nice to test this on the PI.

> Oh, so there is hope. Thanks for looking into it. 
> Im not a programmer myself but im willing to help if I can. 
>> Also, FYI, another option with PPS is to use a usb-serial adapter and
>> feed the PPS in on the CTS or DCD pin.  I tested that on rpi a few
>> months ago and it worked fine.  There's surpisingly little jitter even
>> when the usb bus is heavily loaded with other traffic such as disk or
>> network IO.
> Yes that was going to be my plan B. Good to know that it works.
> /Peter. 

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