如何在Dragonboard 410c上实现一个秒表定时器

本篇将通过一个渠道程序启动一个系统定时器，这个定时器以1S为间隔不断的条用定时器处理函数。每调用函数一次，计数器就会加1、调用设备文件dev/timer_demo中的函数read（），可以读取定时器的值。

（1）驱动程序文件timer_demo.c的具体实现代码如下：

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include /*包括timer.h头文件*/
#include  

#define SECOND_MAJOR 240    /*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？(定义为原子量)*/
  struct timer_list s_timer; /*设备要使用的定时器*/ 1
};

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);//定义定时器到期时间为1秒后  5
  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*/ 2

  init_timer(&second_devp->s_timer);

  //进一步初始化定时器 3 

  second_devp->s_timer.function = &second_timer_handle;

  second_devp->s_timer.expires = jiffies + HZ;

 //激活定时器 4

  add_timer(&second_devp->s_timer); /*添加（注册）定时器*/
  atomic_set(&second_devp->counter,0); //计数清0(原子操作之设置原子量counter为0)  
  return 0;
}
/*文件释放函数*/
int second_release(struct inode *inode, struct file *filp)
{
  del_timer(&second_devp->s_timer);//删除定时器 6
  return 0;
}

/*globalfifo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);//读取原子量counter的整数值
  if(put_user(counter, (int*)buf))//将counter写入用户空间
  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);//组合设备号
  cdev_init(&dev->cdev, &second_fops);//初始化设备结构体
  dev->cdev.owner = THIS_MODULE;
  dev->cdev.ops = &second_fops;
  err = cdev_add(&dev->cdev, devno, 1);//为设备结构体关联设备号
  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;
  }  
  //清空设备结构
  memset(second_devp, 0, sizeof(struct second_dev));
  //转载设备
  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("Sola");
MODULE_LICENSE("Dual BSD/GPL");
module_param(second_major, int, S_IRUGO);
module_init(second_init);
module_exit(second_exit);


（2）驱动程序文件timer_demo_test.c的具体实现代码如下：
#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");
  }
}