Getting access to GPIOs

Now let's look at how we can get access to GPIOs using both the command line (using Bash) and then using the C language.

Bash

Now it's time for an example. A very simple usage is the following one, where we use the gpio91 of the Wandboard to turn an LED on and off. The circuitry is reported in the following figure:

To control the LED, we must set the line as the output, so we should write out in the /sys/class/gpio/gpio91/direction file, but if we wish to set the LED to a precise state by default, it is better to write low, as show here:

root@wb:~# echo low > /sys/class/gpio/gpio91/direction                          

Note

You can now observe that the low value is the default for the out setting, but the preceding setting increases the code readability since it states the intention of the developer exactly.

OK, the LED is still off and we can turn it on and off by writing 1 and 0 in the file value, as shown in the following commands:

root@wb:~# echo 1 > /sys/class...