UM0851 datasheet(209/245 Pages) STMICROELECTRONICS

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UM0851

Miscellaneous device drivers

Doc ID 16604 Rev 2

209/245

9.1.3

GPIO usage in user mode

The following GPIO operations are allowed from user space: request, free, set and get

direction, set and get value.

Note:

Setting a GPIO in interrupt mode is not possible from user space.

Request

User space may ask the kernel to export control of a GPIO pin to user space by writing its

number to this file "/sys/class/gpio/export".

Example: The following line creates a "gpio19 node" for GPIO #19, if it is not requested by

kernel code:

echo 19 > /sys/class/gpio/export

This node can be used for further communication with the GPIO pin.

Free

User space may ask the kernel to take back control of a GPIO pin from user space by writing

its number to this file "/sys/class/gpio/unexport".

Example: The following line removes the "gpio19" node exported using "export" file.

echo 19 > /sys/class/gpio/unexport

Set and get direction

Once a GPIO pin is requested, you can find the following files under /sys/class/gpio/gpiopin/

folder: "direction" and "value". The direction of the GPIO can be set to OUT or IN by writing

"out" or "in" on "direction" file. Here gpiopin, is a file formed after exporting a GPIO pin (for

example, gpio9, gpio42).

Example: setting direction in OUT mode

echo "out" > /sys/class/gpio/gpio42/direction

The direction of GPIO can be read by reading the above file.

Set and get value

The value of the GPIO can be configured, if GPIO is configured in OUT mode and its value

can be read if the GPIO is configured in IN mode. The value can be set by writing 1 or 0 in

the "/sys/class/gpio/gpionr/value" file.

Example: setting gpio pin 42

echo 1 > /sys/class/gpio/gpio42/value

Similarly the value can be read by reading the same file. Here gpiopin, is a file formed after

exporting a GPIO pin (for example gpio9, gpio42).

9.1.4

GPIO usage in kernel mode

The following GPIO operations are allowed from kernel space: Request, set and get

direction and value, and configure GPIO for interrupt.

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