Linux内核高精度定时器hrtimer使用实例

一、内核为高精度定时器重新设计了一套软件架构&＃xff0c;它可以为我们提供纳秒级的定时精度&＃xff0c;以满足对精确时间有迫切需求的应用程序或内核驱动&＃xff0c;以下学习使用hrtimer(high resolution timer)高精度定时器。

二、hrtimer_init函数初始化定时器工作模式。which_clock可以是CLOCK_REALTIME、CLOCK_MONOTONIC、CLOCK_BOOTTIME中的一种&＃xff0c;mode则可以是相对时间HRTIMER_MODE_REL&＃xff0c;也可以是绝对时间HRTIMER_MODE_ABS。

void hrtimer_init(struct hrtimer *timer, clockid_t which_clock,enum hrtimer_mode mode);


 三、设定超时回调函数。

timer.function &＃61; hr_callback;


四、使用hrtimer_start激活该定时器。根据time和mode参数的值计算hrtimer的超时时间&＃xff0c;并设置到timer->expire域。 expire设置的是绝对时间&＃xff0c;所以如果参数mode的值为HRTIMER_MODE_REL&＃xff08;即参数tim的值为相对时间&＃xff09;&＃xff0c;那么需要将tim的值修正为绝对时间&＃xff1a;expire &＃61; tim &＃43; timer->base->get_time()&＃xff0c;调用enqueue_hrtimer&＃xff0c;将hrtimer加入到红黑树中。

int hrtimer_start(struct hrtimer *timer, ktime_t tim,const enum hrtimer_mode mode);


五、使用hrtimer_cancel取消一个hrtimer。

int hrtimer_cancel(struct hrtimer *timer);


六、定时器一旦到期&＃xff0c;function字段指定的回调函数会被调用&＃xff0c;该函数的返回值为一个枚举值&＃xff0c;它决定了该hrtimer是否需要被重新激活。

enum hrtimer_restart {HRTIMER_NORESTART, /* Timer is not restarted */HRTIMER_RESTART, /* Timer must be restarted */
};


七、把hrtimer的到期时间推进一个tick周期&＃xff0c;返回HRTIMER_RESTART表明该hrtimer需要再次启动&＃xff0c;以便产生下一个tick事件。 

hrtimer_forward(timer, now, tick_period);return HRTIMER_RESTART;
}


八、测试代码

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include unsigned int timer_count&＃61;0;
struct hrtimer hrtimer_test_timer;
ktime_t m_kt;
int value&＃61;2000;static enum hrtimer_restart hrtimer_test_timer_poll(struct hrtimer *timer)
{printk("&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;timer_count&＃61;%d &＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;\n",timer_count&＃43;&＃43;);hrtimer_forward(timer, timer->base->get_time(), m_kt);//hrtimer_forward(timer, now, tick_period);//return HRTIMER_NORESTART;return HRTIMER_RESTART;
}int hrtimer_test_ioctl(struct inode *n, struct file *f, unsigned int cmd, unsigned long value){}
ssize_t hrtimer_test_write(struct file *f, const char __user *buf, size_t t, loff_t *len){int i;int ret &＃61; -1;printk("hrtimer Debug buf:%x size:%d\n",*buf,t);if(*buf &＃61;&＃61; &＃39;0&＃39;){printk("hrtimer_start\n");m_kt&＃61;ktime_set(value / 1000, (value % 1000) * 1000000);hrtimer_start(&hrtimer_test_timer,m_kt, HRTIMER_MODE_REL);}else if(*buf &＃61;&＃61; &＃39;1&＃39;){printk("hrtimer_cancel\n");hrtimer_cancel(&hrtimer_test_timer);}return t;
}
static const struct file_operations hrtimer_test_fops &＃61;
{.owner &＃61; THIS_MODULE,.write &＃61; hrtimer_test_write,.unlocked_ioctl &＃61; hrtimer_test_ioctl,
};struct miscdevice hrtimer_test_dev &＃61; {.minor &＃61; MISC_DYNAMIC_MINOR,.name &＃61; "hrtimer_test",.fops &＃61; &hrtimer_test_fops,
};static int __init hrtimer_test_init(void)
{int ret;ret &＃61; misc_register(&hrtimer_test_dev);hrtimer_init(&hrtimer_test_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);hrtimer_test_timer.function &＃61; hrtimer_test_timer_poll;return 0;}static void __exit hrtimer_test_exit(void)
{misc_deregister(&hrtimer_test_dev);
}module_init(hrtimer_test_init);
module_exit(hrtimer_test_exit);
MODULE_AUTHOR("hrtimer");
MODULE_LICENSE("GPL");


九、运行结果