Hardware Reference
In-Depth Information
The ls command shows all the GPIO pins that have be exported. In this case, none have,
so you see only the four GPIO controllers. Export using the export command:
bone# echo 7 > export
bone# ls
export gpio7 gpiochip0 gpiochip32 gpiochip64 gpiochip96
unexport
Now you can see the gpio7 directory. Change into the gpio7 directory and look around:
bone# cd gpio7
bone# ls
active_low direction edge power subsystem uevent value
bone# cat direction
in
bone# cat value
0
Notice that the pin is already configured to be an input pin. (If it wasn't already con-
figured that way, use echo in > direction to configure it.) You can also see that
its current value is 0 — that is, it isn't pressed. Try pressing and holding it and running
again:
bone# cat value
1
The 1 informs you that the switch is pressed. When you are done with GPIO 7, you can
always unexport it:
bone# cd ..
bone# echo 7 > unexport
bone# ls
export gpiochip0 gpiochip32 gpiochip64 gpiochip96 unexport
Writing a GPIO Pin via sysfs
Now, suppose that you want to control an external LED. Recipe 3.2 shows how to wire an
LED to P9_14 . Figure 7-1 shows P9_14 is GPIO 50. Following the approach in Recipe
7.4 , enable GPIO 50 and make it an output:
Search WWH ::




Custom Search