GPIOD_Debian_Raspberry_Pi

Explore GPIOD on Raspberry Pi running Debian Linux

Motivation

Recent explorations demonstrate that Debian (not Debian based Raspberry Pi OS - R-Pi OS) runs well on the Pi Zero and Pi 3B+. One question regarding this is the usability of GPIO which is one of the useful capabilities of the Raspberry Pi.

The library previously used was WiringPi and which seems to be languishing. It's been set aside by its original developer and what seems like the most popular fork has not received an update in nearly a year. Along with looking at GPIO on the Pi, this project will use gpiod to explore GPIO including both shell commands and C/C++ programs.

References

Archived Github repo https://github.com/brgl/libgpiod
Current kernel repo https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/
libgpiod doxygen docs https://libgpiod.readthedocs.io/en/latest/index.html

GPIO access

On Debian the GPIO devices are owned by root and commands that access them thus require root. I have temporarily fixed that by adding the gpio group to /etc/group and changing the ownership and permissions for the device nodes. (The /etc/group entry is copied from Raspbian.)

sudo vim /etc/group
sudo chown root.gpio /dev/gpiochip?
sudo chmod g+rw /dev/gpiochip?

with the result

hbarta@bullpi3b:~$ grep gpio /etc/group
gpio:x:997:hbarta
hbarta@bullpi3b:~$ ls -l /dev/gpiochip0
crw-rw---- 1 root gpio 254, 0 Aug  7 08:25 /dev/gpiochip0
hbarta@bullpi3b:~$

gpioinfo et al now report results w/out the need for root access.

Status

Complete unless the need for further exploration is encountered.

Work in progress working through first CLI commands then various protions of the libgpiod (doxygen) documentation.

name	Doc page	dir	status
CLI exploration	https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/about/	`CLI`	done
High-level API	https://libgpiod.readthedocs.io/en/latest/group__high__level.html	`C_blinky`	done
GPIO chip operations	https://libgpiod.readthedocs.io/en/latest/group__chips.html	`chip_operations`	done
Line info	https://libgpiod.readthedocs.io/en/latest/group__line__info.html	`line_info`	done
Line requests	https://libgpiod.readthedocs.io/en/latest/group__line__request.html	`line_request`	done
Setting line configuration	https://libgpiod.readthedocs.io/en/latest/group__line__config.html	`line_config`	done
Reading & setting line values	https://libgpiod.readthedocs.io/en/latest/group__line__value.html	`line_IO`	done
Line events handling	https://libgpiod.readthedocs.io/en/latest/group__line__event.html	`line_events`	done

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