Robust C Library and Utility for GPIO sysfs Interface in Linux
by Derek Hildreth – Technologic Systems
This comprehensive and easy to read example C code is designed to work alone or included as a library for dealing with general purpose I/O via the sysfs interface in Linux. It can easily be applied to any computer which utilizes the GPIO sysfs interface (both pro and maker boards). Getting started is a breeze. You just need to decide if you’re going to use it as a library (including it into your existing code) or as a stand-alone utility. We’ll talk about in this article, but first and foremost, here’s the source code we’ll be working with:
To get started, download or clone this repository to your board, extract it, and change your directory to it, like so:
wget https://github.com/embeddedarm/gpio-sysfs-demo/archive/master.zip unzip master.zip cd gpio-sysfs-demo-master/
The two important files in this repository came from Technologic System’s GitHub pages:
The included Makefile makes quick work out of compiling the example code mentioned in the sections below, as you’ll see soon enough.
As a stand-alone utility, you can easily copy the resulting gpioctl program to a directory in your current PATH and include in a script or use it for those one-off commands.
To do this, we’ll simply run sudo make install. The Makefile will compile the standalone utility using (essentially) gcc -D CTL gpiolib.c -o gpioctl and then automatically copy it to /usr/local/bin, which is popularly included in PATH. Then, you can run gpioctl –help for instructions on how to use it. For example, say you want to output logical high on DIO #59. You would first set the DIO to be an output, and then you’d set it. Here’s an example of toggling it:
gpioctl –ddrout 59
gpioctl –setout 59
gpioctl –clrout 59
That’s it! If, say, DIO #59 was tied to an LED, you should see the LED turn on and off again.