Linux核心開發之中斷與時鐘(四)

“小王，小王，今天可是這一章節最後一節了，知識點咱們前邊都講過了，今天主要是給你用前邊的東西講一個實際例子---秒字元裝置驅動程式”

  這個驅動程式會在被開啟的時候初始化一個定時器並將其添加到核心定時器鏈表中，每秒輸出一次當前的jiffies，這意味著，定時器處理函數中每次都要修改新的expires。不多說了，看程式碼分析：

#include …//必要的系統標頭檔

#define SECOND_MAJOR 252    /*預設的second的主裝置號*/static int second_major = SECOND_MAJOR;struct second_dev   /*second裝置結構體*/ {  struct cdev cdev; /*cdev結構體*/  atomic_t counter;/* 一共經曆了多少秒？*/  struct timer_list s_timer; /*裝置要使用的定時器*/};struct second_dev *second_devp; /*裝置結構體指標*/static void second_timer_handle(unsigned long arg)   /*定時器處理函數*/ {  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)   /*檔案開啟函數*/ {  /*初始化定時器*/  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（註冊）定時器*/    atomic_set(&second_devp->counter,0); //計數清0

  return 0;}

int second_release(struct inode *inode, struct file *filp)  /*檔案釋放函數*/ {  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讀函數*/ 

{    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 =    /*檔案操作結構體*/ {  .owner = THIS_MODULE,   .open = second_open,   .release = second_release,  .read = second_read,};static void second_setup_cdev(struct second_dev *dev, int index)   /*初始化並註冊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)   /*裝置驅動模組載入函數*/ {  int ret;  dev_t devno = MKDEV(second_major, 0);  /* 申請裝置號*/  if (second_major)    ret = register_chrdev_region(devno, 1, "second");  else  /* 動態申請裝置號 */  {    ret = alloc_chrdev_region(&devno, 0, 1, "second");    second_major = MAJOR(devno);  }  if (ret < 0)    return ret;  /* 動態申請裝置結構體的記憶體*/  second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);  if (!second_devp)    /*申請失敗*/  {    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)   /*模組卸載函數*/ {  cdev_del(&second_devp->cdev);   /*登出cdev*/  kfree(second_devp);     /*釋放裝置結構體記憶體*/  unregister_chrdev_region(MKDEV(second_major, 0), 1); /*釋放裝置號*/}MODULE_AUTHOR("hanyan225");MODULE_LICENSE("Dual BSD/GPL");module_param(second_major, int, S_IRUGO);module_init(second_init);module_exit(second_exit);

下面是測試程式：

#include ..//必要的標頭檔

main(){  int fd;  int counter = 0;  int old_counter = 0;    fd = open("/dev/second", O_RDONLY);   /*開啟/dev/second裝置檔案*/   if (fd !=  - 1)  {    while (1)    {      read(fd,&counter, sizeof(unsigned int));//讀目前經曆的秒數      if(counter!=old_counter)      {      printf("seconds after open /dev/second :%d\n",counter);      old_counter = counter;      }    }      }  else  {    printf("Device open failure\n");  }}

當我們編譯完驅動程式，並運行了測試程式後，會看到應用程式不斷輸出自開啟/dev/second以來經曆的秒數。如下：#./testseconds after open /dev/second 1seconds after open /dev/second 2....再帶一個中斷，看看核心輸出操作如下：#tar –f /var/logs/messagecurrent jiffies is 18569current jiffies is 18669

current jiffies is 18769
..

..

 

“小王,Linux裝置驅動之中斷與時鐘也算說完了，告一段落了，也不知道你明白沒，沒明白，也沒關係，不是有我嗎，只是不要一早吵醒我就好，下次我們就要開始系統記憶體方面的東西了…”我說。

“好，小濤哥，我好好看看，不懂就問你，呵呵..”小王銀鈴般笑著還伴著怪臉，真是讓人…