6、秒设备驱动与应用程序（内核定时器的应用)

驱动：
======================================================================*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include /*包括timer.h头文件*/
#include

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

static int second_major = SECOND_MAJOR;

/*second设备结构体*/
struct second_dev
{
  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*/

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

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

/*读函数*/
static ssize_t second_read(struct file *filp, char __user *buf, size_t count,
  loff_t *ppos)
{ 
  int counter;
 
  counter = atomic_read(&second_devp->counter);
  if(put_user(counter, (int*)buf))
      return - EFAULT;
  else
      return sizeof(unsigned int); 
}

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

/*初始化并注册cdev*/
static void second_setup_cdev(struct second_dev *dev, int index)
{
  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);
}

/*设备驱动模块加载函数*/
int second_init(void)
{
  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);
}

/*模块卸载函数*/
void second_exit(void)
{
  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("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");

module_param(second_major, int, S_IRUGO);

module_init(second_init);
module_exit(second_exit);

应用：
/*======================================================================
    A test program to access /dev/second
    This example is to help understand kernel timer
   
    The initial developer of the original code is Baohua Song
    . All Rights Reserved.
======================================================================*/
#include
#include
#include
#include
#include
#include

main()
{
  int fd;
  int counter = 0;
  int old_counter = 0;
 
  /*打开/dev/second设备文件*/
  fd = open("/dev/second", O_RDONLY);
  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");
  }
}
最终的测试：
/ $ insmod second.ko
/ $ cat /proc/devices
Character devices:
  1 mem
  2 pty
  3 ttyp
  4 /dev/vc/0
  4 tty
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
 10 misc
 13 input
 14 sound
 29 fb
 81 video4linux
 89 i2c
 90 mtd
128 ptm
136 pts
180 usb
188 ttyUSB
204 s3c2410_serial
252 second
253 globalfifo

 $ mknod /dev/second c 252 0
 $ ./second_test
current jiffies is 1748267
seconds after open /dev/second :1
current jiffies is 1748467
seconds after open /dev/second :2
current jiffies is 1748667
seconds after open /dev/second :3
current jiffies is 1748867
seconds after open /dev/second :4
current jiffies is 1749067
seconds after open /dev/second :5
current jiffies is 1749267