Linux 4.14 —— 内核定时器hrtimer的使用

本文主要是介绍Linux 4.14 —— 内核定时器hrtimer的使用，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1. struct hrtimer

2. 如何使用

3. 示例

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1. struct hrtimer

/*** struct hrtimer - the basic hrtimer structure* @node:	timerqueue node, which also manages node.expires,*		the absolute expiry time in the hrtimers internal*		representation. The time is related to the clock on*		which the timer is based. Is setup by adding*		slack to the _softexpires value. For non range timers*		identical to _softexpires.* @_softexpires: the absolute earliest expiry time of the hrtimer.*		The time which was given as expiry time when the timer*		was armed.* @function:	timer expiry callback function* @base:	pointer to the timer base (per cpu and per clock)* @state:	state information (See bit values above)* @is_rel:	Set if the timer was armed relative** The hrtimer structure must be initialized by hrtimer_init()*/
struct hrtimer {struct timerqueue_node		node;ktime_t				_softexpires;enum hrtimer_restart		(*function)(struct hrtimer *);struct hrtimer_clock_base	*base;u8				state;u8				is_rel;
};

        定时器的到期时间用ktime_t来表示，_softexpires字段记录了时间，定时器一旦到期，function字段指定的回调函数会被调用，该函数的返回值为一个枚举值，它决定了该hrtimer是否需要被重新激活：

/** Return values for the callback function*/
enum hrtimer_restart {HRTIMER_NORESTART,	/* Timer is not restarted */HRTIMER_RESTART,	/* Timer must be restarted */
};

2. 如何使用

1）需要定义一个hrtimer结构的实例

2）用hrtimer_init函数对它进行初始化

/*** hrtimer_init - initialize a timer to the given clock* @timer:	the timer to be initialized* @clock_id:	the clock to be used* @mode:	timer mode abs/rel*/
void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,enum hrtimer_mode mode);

        其中clock_id可以是CLOCK_REALTIME、CLOCK_MONOTONIC、CLOCK_BOOTTIME中的一种，mode则可以是相对时间HRTIMER_MODE_REL，也可以是绝对时间HRTIMER_MODE_ABS。

3）设定回调函数

timer.function = hr_callback;

4）如果定时器无需指定一个到期范围，可以在设定回调函数后直接使用hrtimer_start激活该定时器；如果需要指定到期范围，则可以使用hrtimer_start_range_ns激活定时器。函数原型：

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

5）要取消一个hrtimer，使用hrtimer_cancel

int hrtimer_cancel(struct hrtimer *timer);

3. 示例

static struct hrtimer battery_kthread_timer;enum hrtimer_restart battery_kthread_hrtimer_func(struct hrtimer *timer)  
{  //bat_thread_wakeup();do somethingreturn HRTIMER_NORESTART;  
}  
void battery_kthread_hrtimer_init(void)  
{  ktime_t ktime;  ktime = ktime_set(1, 0);    //set  1s 定时  hrtimer_init(&battery_kthread_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);  battery_kthread_timer.function = battery_kthread_hrtimer_func;  hrtimer_start(&battery_kthread_timer, ktime, HRTIMER_MODE_REL);  }  

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