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:

https://github.com/embeddedarm/gpio-sysfs-demo

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:

• https://github.com/embeddedarm/ts4900-utils/blob/master/src/gpiolib.c
• https://github.com/embeddedarm/ts4900-utils/blob/master/src/gpiolib.h

The included Makefile makes quick work out of compiling the example code mentioned in the sections below, as you’ll see soon enough.

Stand-Alone Utility

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.

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