GPIO¶

GPIO state¶

The current state of the systems' GPIOs can be obtained in user-mode, as shown in the following example:

$ cat /sys/kernel/debug/gpio

The above command on Variscite's VAR-DVK-MX6 will show the following:

root@varsomam33:~# cat /sys/kernel/debug/gpio
GPIOs 0-31, platform/44e07000.gpio, gpio:

GPIOs 32-63, platform/4804c000.gpio, gpio:
 gpio-60  (cd                  ) in  lo IRQ

GPIOs 64-95, platform/481ac000.gpio, gpio:
 gpio-82  (wp                  ) in  lo

GPIOs 96-127, platform/481ae000.gpio, gpio:
 gpio-100 (button0             ) in  hi IRQ
 gpio-105 (kim                 ) out lo
 gpio-117 (wlan-en-regulator   ) out lo

GPIOs 510-511, platform/50000000.gpmc, omap-gpmc:
 gpio-510 (ready               ) in  hi
root@varsomam33:~#

Each GPIO is defined as in or out and the state is shown as lo or hi.

For example , SD-Card card-detect:
When SD-Card is removed the state will be:

 gpio-60  (cd                  ) in  hi IRQ

When the SD-Card is plugged the state will be:

 gpio-60  (cd                  ) in  lo IRQ

Manipulating a single GPIO via /sys/class/gpio¶

GPIOs in AM33 are grouped in groups of 32 pins.
For example GPIO1_3 belong to the first group pin 3. Its absolute number will be 3.

GPIO7_4 will be (7-1)*32+4=196.

Lets assume that you defined this GPIO in the device tree. We will show in the following sections how to define it.

To configure as output:

$ echo 196 > /sys/class/gpio/export
$ echo out > /sys/class/gpio/gpio196/direction

Set GPIO high:

$ echo 1 > /sys/class/gpio/gpio196/value

Set GPIO low:

$ echo 0 > /sys/class/gpio/gpio196/value

To configure as input:

$ echo 196 > /sys/class/gpio/export
$ echo in > /sys/class/gpio/gpio196/direction

$ cat /sys/class/gpio/gpio196/value

Will read the current value.

Reference reading¶

http://processors.wiki.ti.com/index.php/Linux_PSP_GPIO_Driver_Guide