Add a wait_for_edge() function about pifacecommon HOT 3 OPEN

I am also looking for such a function

from pifacecommon.

I've had an idea for this for a very long time - just not got around to implementing it. I'm not even sure if Raspbian is still organised like this but I imagine it would work something like this:

1. Bring up GPIO25 in userland with echo 25 > /sys/class/gpio/export.

2. In Python, use epoll to wait on changes:

   with open('/sys/class/gpio/gpio25/value', 'r') as gpio25:
       epoll = select.epoll()
       epoll.register(gpio25, select.EPOLLIN | select.EPOLLET)
       events = epoll.poll()  #  wait for interrupt
       epoll.close()
   

This could be wrapped up into a wait_for_edge function. This is how the C libs work: https://github.com/piface/libmcp23s17/blob/master/src/mcp23s17.c#L189-L203

from pifacecommon.

libgpiod is the future of Linux gpio, so when someone gets around to implementing this, it should use that:

• https://github.com/brgl/libgpiod
• https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git

from pifacecommon.