UM0851 datasheet(210/245 Pages) STMICROELECTRONICS

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Miscellaneous device drivers

UM0851

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Doc ID 16604 Rev 2

Request

You can request a GPIO pin by calling following function:

/*Gpio: is gpio pin number to be requested.

Label: is a string passed by user as a unique identification of user. */

int gpio_request(unsigned gpio, const char *label);

Passing invalid GPIO numbers to gpio_request() will fail, as will requesting GPIOs that have

already been claimed with that call. The return value of gpio_request() must be checked. On

error, standard Linux errors are returned, else 0 is returned.

Free

After using a GPIO pin that you previously requested, you must free it. You can free a GPIO

pin by calling the following function:

/* Gpio: is gpio pin number already requested */

void gpio_free(unsigned gpio);

Passing an invalid GPIO number to gpio_free() will fail.

Set direction

After requesting a GPIO pin, you must set its direction. This can be done using following

function:

/* Gpio: is gpio pin number.

Value: is value to be set, 0 or 1.*/

int gpio_direction_output(unsigned gpio, int value);

The return value is zero for success, else a negative errno. You must check the return value,

since the get/set calls do not return errors and a wrong configuration is possible. Setting the

direction can fail if the GPIO number is invalid, or when that particular GPIO can not be used

in that mode.

Set and get value

After the direction of GPIO is set, its value can be read or written. You can write a value to a

GPIO in OUT mode and can read a value from a GPIO in IN mode. This can be done using

following functions:

/* Gpio: is gpio pin number.

Value: is value to be set, 0 or 1. */

void gpio_set_value(unsigned gpio, int value);

/* Gpio: is gpio pin number. */

int gpio_get_value(unsigned gpio);

The values are Boolean, zero for low, nonzero for high.

9.1.5

GPIO in interrupt mode

GPIO pins can be configured in interrupt mode. They support rising, falling or both edge

triggered interrupts and high or low level triggered interrupts.

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