Linux Kernel training (2) Gpio

General Purpose Input Output (通用輸入/輸出)簡稱爲GPIO，或總線擴展器，利用工業標準I2C、SMBus™或SPI™接口簡化了I/O口的擴展。當微控制器或芯片組沒有足夠的 I/O端口，或當系統需要採用遠端串行通信或控制時，GPIO產品能夠提供額外的控制和監視功能。

One Module driver example,

 #include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/gpio.h>
#include <linux/delay.h>

#define SNOWBALL_LED_GPIO_NR    142
#define LED_OFF            0
#define LED_ON            1

static struct delayed_work blinking_work;
static int i = 0;

static void blink_function(struct work_struct *work)
{
  gpio_set_value(SNOWBALL_LED_GPIO_NR, i++ % 2);
  schedule_delayed_work(&blinking_work, 1000);
}

static int start_blinking(void)
{
  int err = 0;

  INIT_DELAYED_WORK(&blinking_work, blink_function);

  printk(KERN_ERR "We're starting our module!\n");

  err = gpio_request(SNOWBALL_LED_GPIO_NR, "led_blinking");
  if (err) {
    printk(KERN_ERR "GPIO request failed %d\n", err);
    goto request_failed;
  }

  err = gpio_direction_output(SNOWBALL_LED_GPIO_NR, LED_OFF);
  if (err) {
    printk(KERN_ERR "gpio_direction_output failed %d\n", err);
    gpio_free(SNOWBALL_LED_GPIO_NR);
    goto request_failed;
  }

  schedule_delayed_work(&blinking_work, 1);

  request_failed:
  return err;
}

static void stop_blinking(void) {
  printk(KERN_ERR "Bye, cruel world\n");
  cancel_delayed_work_sync(&blinking_work);
  gpio_free(SNOWBALL_LED_GPIO_NR);
}

module_init(start_blinking);
module_exit(stop_blinking);

MODULE_LICENSE("GPL");