Linux设备驱动之四----带中断的驱动程序

前言：

本示例的目的是读取按键按下或松开时的按键值

驱动程序如下：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>

static struct class *thirddrv_class;
static struct class_device	*thirddrv_class_dev;

volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;

volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;

//定义并初始化一个等待队列头button_waitq

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

/* 中断事件标志, 中断服务程序将它置1，third_drv_read将它清0 */
static volatile int ev_press = 0;

struct pin_desc{
unsigned int pin;
unsigned int key_val;
};

/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;

struct pin_desc pins_desc[4] = {
{S3C2410_GPF0, 0x01},
{S3C2410_GPF2, 0x02},
{S3C2410_GPG3, 0x03},
{S3C2410_GPG11, 0x04},
};

/*
* 确定按键值
*/
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
struct pin_desc * pindesc = (struct pin_desc *)dev_id;
unsigned int pinval;

pinval = s3c2410_gpio_getpin(pindesc->pin);

if (pinval)
{
/* 松开 */
key_val = 0x80 | pindesc->key_val;
}
else
{
/* 按下 */
key_val = pindesc->key_val;
}

ev_press = 1;                  /* 表示中断发生了 */
wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */

return IRQ_RETVAL(IRQ_HANDLED);
}

static int third_drv_open(struct inode *inode, struct file *file)
{
/* 配置相应的引脚为中断引脚 */

request_irq(IRQ_EINT0,  buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);
request_irq(IRQ_EINT2,  buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);
request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);
request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);

return 0;
}

ssize_t third_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;

/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);

/* 如果有按键动作, 返回键值 */
copy_to_user(buf, &key_val, 1);
ev_press = 0;

return 1;
}

int third_drv_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT0, &pins_desc[0]);
free_irq(IRQ_EINT2, &pins_desc[1]);
free_irq(IRQ_EINT11, &pins_desc[2]);
free_irq(IRQ_EINT19, &pins_desc[3]);
return 0;
}

static struct file_operations sencod_drv_fops = {
.owner   =  THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open    =  third_drv_open,
.read	 =	third_drv_read,
.release =  third_drv_close,
};

int major;
static int third_drv_init(void)
{
major = register_chrdev(0, "third_drv", &sencod_drv_fops);

thirddrv_class = class_create(THIS_MODULE, "third_drv");

thirddrv_class_dev = class_device_create(thirddrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */

gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
gpfdat = gpfcon + 1;

gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);
gpgdat = gpgcon + 1;

return 0;
}

static void third_drv_exit(void)
{
unregister_chrdev(major, "third_drv");
class_device_unregister(thirddrv_class_dev);
class_destroy(thirddrv_class);
iounmap(gpfcon);
iounmap(gpgcon);
return 0;
}

module_init(third_drv_init);

module_exit(third_drv_exit);

MODULE_LICENSE("GPL");

注：

1>

request_irq(IRQ_EINT0,  buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);

表示向系统申请中断，其中buttons_irq是中断处理函数，所以我们需要在驱动里边去实现这个中断处理函数

如：static irqreturn_t buttons_irq(int irq, void *dev_id){ }

与此同时，free_irq(IRQ_EINT0, &pins_desc[0]);表示释放对应的中断

2>

阻塞从字面上听起来似乎意味着低效率，实则不然，如果设备驱动不阻塞，则用户想获取设备资源只能不停地查询，这法尔会无谓的耗费CPU资源，

而阻塞访问时，不能获取资源的进程将进入休眠，它将CPU资源“礼让”给其他进程。

因为阻塞的进程会进入休眠状态，因此，必须确保有一个地方能够唤醒休眠的进程，否则，进程真的就“寿终正寝”了。唤醒进程的地方最大可能就是

发生在中断里边，因为硬件资源获得的同时，往往伴随着一个中断。

在这里，我们是用wait_event_interruptible(button_waitq, ev_press);来实现阻塞，让出 CPU资源给其他进程

其中，button_waitq参数表示等待button_waitq作为等待队列头的等待队列被唤醒；而且第二个参数ev_press必须满足，否则，继续阻塞；

在中断函数中，通过wake_up_interruptible(&button_waitq); 唤醒button_waitq的等待队列头；

测试程序如下：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

/* thirddrvtest
*/
int main(int argc, char **argv)
{
int fd;
unsigned char key_val;

fd = open("/dev/buttons", O_RDWR);
if (fd < 0)
{
printf("can't open!\n");
}

while (1)
{
read(fd, &key_val, 1);
printf("key_val = 0x%x\n", key_val);
}

return 0;
}

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