Linux内核开发之中断与时钟(四)

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原创最新推荐文章于 2026-03-10 01:56:51 发布 328 阅读 AI 写同款· GEO 优化 ›

时钟中断（1）在所有外部中断中，时钟中断起着特殊的作用。因为计算机是以精确的时间进行数值运算的数据处理的，最基本的时间单元是时钟周期，例如取指令，执行指令，存取内存等，我们将要讨论的是操作系统建立的时间系统，这个时间系统是整个操作系统活动的动力。阅读详情

“小王，小王，今天可是这一章节最后一节了，知识点咱们前边都讲过了，今天主要是给你用前边的东西讲一个实际例子---秒字符设备驱动程序”

这个驱动程序会在被打开的时候初始化一个定时器并将其添加到内核定时器链表中，每秒输出一次当前的jiffies，这意味着，定时器处理函数中每次都要修改新的expires。不多说了，看代码分析：

#include …//必要的系统头文件

#define SECOND_MAJOR 252    /*预设的second的主设备号*/

static int second_major = SECOND_MAJOR;
struct second_dev   /*second设备结构体*/ 
{
  struct cdev cdev; /*cdev结构体*/
  atomic_t counter;/* 一共经历了多少秒？*/
  struct timer_list s_timer; /*设备要使用的定时器*/
};
struct second_dev *second_devp; /*设备结构体指针*/

static void second_timer_handle(unsigned long arg)   /*定时器处理函数*/ 
{
  mod_timer(&second_devp->s_timer,jiffies + HZ);
  atomic_inc(&second_devp->counter);
  printk(KERN_NOTICE "current jiffies is %ld\n", jiffies);
}

int second_open(struct inode *inode, struct file *filp)   /*文件打开函数*/ 
{
  /*初始化定时器*/
  init_timer(&second_devp->s_timer);
  second_devp->s_timer.function = &second_timer_handle;
  second_devp->s_timer.expires = jiffies + HZ;
  
  add_timer(&second_devp->s_timer); /*添加（注册）定时器*/
  
  atomic_set(&second_devp->counter,0); //计数清0

  return 0;
}

int second_release(struct inode *inode, struct file *filp)  /*文件释放函数*/ 
{
  del_timer(&second_devp->s_timer);
  return 0;
}

static ssize_t second_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)   /*globalfifo读函数*/

{  
  int counter;
  
  counter = atomic_read(&second_devp->counter);
  if(put_user(counter, (int*)buf))
  	return - EFAULT;
  else
  	return sizeof(unsigned int);  
}

static const struct file_operations second_fops =    /*文件操作结构体*/ 
{
  .owner = THIS_MODULE, 
  .open = second_open, 
  .release = second_release,
  .read = second_read,
};

static void second_setup_cdev(struct second_dev *dev, int index)   /*初始化并注册cdev*/ 
{
  int err, devno = MKDEV(second_major, index);

  cdev_init(&dev->cdev, &second_fops);
  dev->cdev.owner = THIS_MODULE;
  dev->cdev.ops = &second_fops;
  err = cdev_add(&dev->cdev, devno, 1);
  if (err)
    printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}

int second_init(void)   /*设备驱动模块加载函数*/ 
{
  int ret;
  dev_t devno = MKDEV(second_major, 0);

  /* 申请设备号*/
  if (second_major)
    ret = register_chrdev_region(devno, 1, "second");
  else  /* 动态申请设备号 */
  {
    ret = alloc_chrdev_region(&devno, 0, 1, "second");
    second_major = MAJOR(devno);
  }
  if (ret < 0)
    return ret;
  /* 动态申请设备结构体的内存*/
  second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);
  if (!second_devp)    /*申请失败*/
  {
    ret =  - ENOMEM;
    goto fail_malloc;
  }

  memset(second_devp, 0, sizeof(struct second_dev));
  second_setup_cdev(second_devp, 0);

  return 0;

  fail_malloc: unregister_chrdev_region(devno, 1);
}

void second_exit(void)   /*模块卸载函数*/ 
{
  cdev_del(&second_devp->cdev);   /*注销cdev*/
  kfree(second_devp);     /*释放设备结构体内存*/
  unregister_chrdev_region(MKDEV(second_major, 0), 1); /*释放设备号*/
}
MODULE_AUTHOR("hanyan225");
MODULE_LICENSE("Dual BSD/GPL");
module_param(second_major, int, S_IRUGO);
module_init(second_init);
module_exit(second_exit);

下面是测试程序：

#include ..//必要的头文件

main()
{
  int fd;
  int counter = 0;
  int old_counter = 0;
  
  fd = open("/dev/second", O_RDONLY);   /*打开/dev/second设备文件*/ 
  if (fd !=  - 1)
  {
    while (1)
    {
      read(fd,&counter, sizeof(unsigned int));//读目前经历的秒数
      if(counter!=old_counter)
      {	
      	printf("seconds after open /dev/second :%d\n",counter);
      	old_counter = counter;
      }	
    }    
  }
  else
  {
    printf("Device open failure\n");
  }
}