如何在Dragonboard 410c上實現(xiàn)一個秒表定時器

本篇將通過一個渠道程序啟動一個系統(tǒng)定時器，這個定時器以1S為間隔不斷的條用定時器處理函數(shù)。每調(diào)用函數(shù)一次，計數(shù)器就會加1、調(diào)用設(shè)備文件dev/timer_demo中的函數(shù)read（），可以讀取定時器的值。

（1）驅(qū)動程序文件timer_demo.c的具體實現(xiàn)代碼如下：

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include /*包括timer.h頭文件*/
#include ?

#define SECOND_MAJOR 240 ? ?/*預(yù)設(shè)的second的主設(shè)備號*/
static int second_major = SECOND_MAJOR;

/*second設(shè)備結(jié)構(gòu)體*/
struct second_dev
{
? struct cdev cdev; /*cdev結(jié)構(gòu)體*/
? atomic_t counter;/* 一共經(jīng)歷了多少秒？(定義為原子量)*/
??struct timer_list s_timer; /*設(shè)備要使用的定時器*/ 1
};

struct second_dev *second_devp; /*設(shè)備結(jié)構(gòu)體指針*/

/*定時器處理函數(shù)*/
static void second_timer_handle(unsigned long arg)
{
??mod_timer(&second_devp->s_timer,jiffies + HZ);//定義定時器到期時間為1秒后 ?5
? atomic_inc(&second_devp->counter);
? printk(KERN_NOTICE "current jiffies is %ld\n", jiffies);
}

/*文件打開函數(shù)*/
int second_open(struct inode *inode, struct file *filp)
{
??/*初始化定時器*/ 2

? init_timer(&second_devp->s_timer);

??//進一步初始化定時器 3?

??second_devp->s_timer.function = &second_timer_handle;

? second_devp->s_timer.expires = jiffies + HZ;

?//激活定時器 4

??add_timer(&second_devp->s_timer); /*添加（注冊）定時器*/
? atomic_set(&second_devp->counter,0); //計數(shù)清0(原子操作之設(shè)置原子量counter為0) ?
? return 0;
}
/*文件釋放函數(shù)*/
int second_release(struct inode *inode, struct file *filp)
{
??del_timer(&second_devp->s_timer);//刪除定時器 6
??return 0;
}

/*globalfifo讀函數(shù)*/
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);//讀取原子量counter的整數(shù)值
? if(put_user(counter, (int*)buf))//將counter寫入用戶空間
? return - EFAULT;
? else
? return sizeof(unsigned int); ?
}

/*文件操作結(jié)構(gòu)體*/
static const struct file_operations second_fops =
{
? .owner = THIS_MODULE,?
? .open = second_open,?
? .release = second_release,
? .read = second_read,
};

/*初始化并注冊cdev*/
static void second_setup_cdev(struct second_dev *dev, int index)
{
? int err, devno = MKDEV(second_major, index);//組合設(shè)備號
? cdev_init(&dev->cdev, &second_fops);//初始化設(shè)備結(jié)構(gòu)體
? dev->cdev.owner = THIS_MODULE;
? dev->cdev.ops = &second_fops;
? err = cdev_add(&dev->cdev, devno, 1);//為設(shè)備結(jié)構(gòu)體關(guān)聯(lián)設(shè)備號
? if (err)
? ? printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}

/*設(shè)備驅(qū)動模塊加載函數(shù)*/
int second_init(void)
{
? int ret;
? dev_t devno = MKDEV(second_major, 0);
? ?/* 申請設(shè)備號*/
? if (second_major)
? ? ret = register_chrdev_region(devno, 1, "second");
? else ?/* 動態(tài)申請設(shè)備號 */
? {
? ? ret = alloc_chrdev_region(&devno, 0, 1, "second");
? ? second_major = MAJOR(devno);
? }
? if (ret < 0)
? ? return ret;
? /* 動態(tài)申請設(shè)備結(jié)構(gòu)體的內(nèi)存*/
? second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);
? if (!second_devp) ? ?/*申請失敗*/
? {
? ? ret = ?- ENOMEM;
? ? goto fail_malloc;
? }??
? //清空設(shè)備結(jié)構(gòu)
? memset(second_devp, 0, sizeof(struct second_dev));
? //轉(zhuǎn)載設(shè)備
? second_setup_cdev(second_devp, 0);
? return 0;
? fail_malloc: unregister_chrdev_region(devno, 1);

}

/*模塊卸載函數(shù)*/
void second_exit(void)
{
? cdev_del(&second_devp->cdev); ? /*注銷cdev*/
? kfree(second_devp); ? ? /*釋放設(shè)備結(jié)構(gòu)體內(nèi)存*/
? unregister_chrdev_region(MKDEV(second_major, 0), 1); /*釋放設(shè)備號*/
}

MODULE_AUTHOR("Sola");
MODULE_LICENSE("Dual BSD/GPL");
module_param(second_major, int, S_IRUGO);
module_init(second_init);
module_exit(second_exit);


（2）驅(qū)動程序文件timer_demo_test.c的具體實現(xiàn)代碼如下：
#include
#include
#include
#include
#include
#include
main()
{
? int fd;
? int counter = 0;
?int old_counter = 0;

? /*打開/dev/second設(shè)備文件*/
? fd = open("/dev/second", O_RDONLY);
? if (fd != ?- 1)
? {
? ?while (1)
? ? {
? ? ? read(fd,&counter, sizeof(unsigned int));//讀目前經(jīng)歷的秒數(shù)

? ? ? if(counter!=old_counter)

? ? ? {?
? ? ? printf("seconds after open /dev/second :%d\n",counter);
? ? ? old_counter = counter;

? ? ? }?
? ? } ? ?
? }
? else
? {
? printf("Device open failure\n");
? }
}