Linux驱动学习笔记（3）

从之前的查表方式检测按键是否被按下的情况来看，完全霸占着CPU，不能让CPU干其他的事。如果用中断检测的方式来检测按键则可以避免这个问题，当有按键被按下的时候，就会产生中断。

#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;


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GPF0,2为输入引脚 */
    /* 配置GPG3,11为输入引脚 */ /* 有中断请求时，会自动将能设置为中断模式的引脚设为中断模式，所以这里不用配置引脚模式，都自动配置成了中断模式 11 */
/* request_irq参数可以参考Linux源代码里面的其他代码，其中IRQT_BOTHEDGE表示是双边沿触发 */
    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) // 强制为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;   // 清零

    return 1;
}


int third_drv_close(struct inode *inode, struct file *file)
{
    free_irq(IRQ_EINT0, &pins_desc[0]);   // 释放中断，两个参数，中断号和引脚描述
    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，指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);  // 自动分配主设备号

    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);  // 地址映射
    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");

测试程序：

#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);                  //进入内核态的read函数
        printf("key_val = 0x%x\n", key_val);
    }

    return 0;
}

也是通过一个死循环，如果没有按键按下就会永远在在那里等待。但占用CPU资源得到很好的改善。