From Variscite Wiki

1 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-AM43 will show the following:

root@varsomam43:~# cat /sys/kernel/debug/gpio
GPIOs 0-31, platform/44e07000.gpio, gpio:
 gpio-6   (cd                  ) in  lo IRQ

GPIOs 32-63, platform/4804c000.gpio, gpio:
 gpio-48  (kim                 ) out lo
 gpio-52  (vmmcwl_fixed        ) out lo

GPIOs 64-95, platform/481ac000.gpio, gpio:

GPIOs 96-127, platform/481ae000.gpio, gpio:

GPIOs 128-159, platform/48320000.gpio, gpio:
 gpio-136 (?                   ) out lo
 gpio-154 (?                   ) out lo
 gpio-157 (ft5x06_irq_gpio     ) in  hi IRQ

GPIOs 160-191, platform/48322000.gpio, gpio:
 gpio-164 (sw6                 ) in  hi IRQ
 gpio-165 (sw5                 ) in  hi IRQ
 gpio-166 (sw4                 ) in  hi IRQ
 gpio-167 (vtt_fixed           ) out hi

GPIOs 510-511, platform/50000000.gpmc, omap-gpmc:

Each GPIO is defined as in or out and the state is shown as lo or hi.
For example , SW4 the Menu Button:
When SW4 is pressed the state will be:

 gpio-166 (sw4                 ) in  lo IRQ

When SW4 is released the state will be:

 gpio-166 (sw4                 ) in  hi IRQ

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

GPIOs in the AM437X are grouped in 6 groups of 32 pins from GPIO0-GPIO5.
For example GPIO0_3 belongs to the first group pin 3. Its absolute number will be 3.
GPIO5_8 will be (5)*32+8=168.
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 168 > /sys/class/gpio/export
$ echo out > /sys/class/gpio/gpio168/direction

Set GPIO low:

$ echo 0 > /sys/class/gpio/gpio168/value

Set GPIO high:

$ echo 1 > /sys/class/gpio/gpio168/value

To configure as input:

$ echo 168 > /sys/class/gpio/export
$ echo in > /sys/class/gpio/gpio168/direction
$ cat /sys/class/gpio/gpio168/value

Will read the current value.

3 Reference reading