pifacecommon

Common functions for interacting with PiFace products.

Fork Documentation

This is a fork of https://github.com/piface/pifacecommon to make it work on a Raspberry Pi 4 with Raspberry Pi OS based on Debian Bookworm and a Linux Kernel 6.x.

TL;DR

The only difference is the GPIO #25 number in interrupts.py, which becomes 537 (512 + 25).

Longer version:

The Linux Kernel has changed the way GPIOs are being addressed -- since circa 2015 the "sysfs" interface has been slowly deprecated, to be entirely replaced by 2020. interrupts.py makes an access to /sys/class/gpio/gpio25/ which does not exist in the recent kernel gpio driver.

However, the feature has not been entirely removed. It still works, with a little caveat: the sysfs interface now explicitly lists each gpio chip, with a "base number" and a number of GPIOs handled. A user-level tool gpioinfo lists all the pins.

In our case, we want gpiochip0 which is defined as:

/sys/class/gpio/gpiochip512/base = 512
/sys/class/gpio/gpiochip512/ngpio = 58

There are ways to iterate all the pins. There's even a GPIO module for Python. However on the RPi 4, we know the legacy GPIO25 maps to offset #25 in the gpiochip0 with a base of 512. Thus, the new pin number is 512 + 25 = 537.

Original Documentation (obsolete)

http://pifacecommon.readthedocs.org/

You can also find the documentation installed at:

/usr/share/doc/python3-pifacecommon/

Install

On a Raspberry Pi 4 with Debian Bookworm, the old recommendation from using pip3 install pifacecommon is now obsolete.

The modern recommendation is to install PIP modules in a Python Virtual Environment, to avoid breaking APT-based system libraries.

Install the forked version of pifacecommon like this:

# Create a new Python Virtual Environment
$ python3 -m venv my_piface
$ cd my_piface

# Install PiFaceCommon from a locally checked out source
$ git clone https://github.com/ralfoide/pifacecommon.git
$ bin/pip3 install pifacecommon/

# Install PiFaceDigitalio from the repository
$ bin/pip3 install pifacedigitalio

# Try one of the examples
$ git clone https://github.com/piface/pifacedigitalio.git
$ bin/python3 pifacedigitalio/examples/presslights.py

Note: Allegedly, you can still install PIP modules globally if you pass the aptly-named argument --break-system-packages to pip.

You will also need to set up automatic loading of the SPI kernel module which can be done with the latest version of raspi-config. Run:

$ sudo raspi-config

Then navigate to Advanced Options, SPI and select yes.

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