Introduction

There are different ways and tools to access BeagleBone's GPIO hardware from programs, but sysfs is a simple one that is supported by the Linux kernel and makes the devices visible in the file system so we can work from the command line without needing to write any code. For simple applications you can use it with the sysfs way, either interactively or by putting the commands in shell scripts.

Sysfs is a pseudo filesystem provided by the Linux kernel that makes information about various kernel subsystems, hardware devices, and device drivers available in user space through virtual files. GPIO devices appear as part of sysfs.

RaspberryPi 4 (RBPi4)

Note: This code and commands have been tested directly on a RaspberryPi4. The GPIO process for the RBPi4 is quiete different fro, the BeagleBone Boards, please considers the instructions for RBPi4 or BBB.

Basic considerations

First steps

The system has some sysfs GPIO drivers already loaded, you can search for them at /sys/class/gpio/:

ls /sys/class/gpio
export  gpiochip0  gpiochip504  unexport

We'll look at how to use this interface next. Note that the device names starting with "gpiochip" are the GPIO controllers and we won't directly use them.

Next, the basic steps to use a GPIO pin from the sysfs interface are:

1. Export the pin.
2. Set the pin direction (input or output).
3. If an output pin, set the level to low or high.
4. If an input pin, read the pin's level (low or high).
5. When the gpio is not used anymore, unexport the pin.

Thus, to make available the GPIO24 as an output and write a logic 1, we should do:

Export the GPIO24 by

echo 24 >> /sys/class/gpio/export

then, the gpio24 linksys file is abilable at

ls /sys/class/gpio/
export  gpio24  gpiochip0  gpiochip504  unexport

you can go now and observe inside the gpio24 folder a series of configuration files

ls /sys/class/gpio/gpio24/
active_low  device  direction  edge  power  subsystem  uevent  value

the ones that we require for now are the direction and value, then, to make the GPIO24 an output write a logic 1 (3V):

echo out >> /sys/class/gpio/gpio24/direction
echo 1 >> /sys/class/gpio/gpio24/value

BeagleBone Black

Basic considerations

Your work and description here

Add here the description and the code that you develop to create a bash function to configure any GPIO to write (output) or read(input) by passing arguments to your command gpio.sh.