初入android驱动开发之定时器hrtime

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我是靠谱客的博主贪玩热狗，最近开发中收集的这篇文章主要介绍初入android驱动开发之定时器hrtime，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

hrtime，高精度定时器，这里有篇文章，介绍hrtime相关的知识。点击打开链接

这里，主要介绍如何利用hrtime来模拟PWM的方波。

1 相关的方法：

<span style="font-size:14px;">/**
 * hrtimer_start - (re)start an hrtimer on the current CPU
 * @timer:	the timer to be added
 * @tim:	expiry time
 * @mode:	expiry mode: absolute (HRTIMER_ABS) or relative (HRTIMER_REL)
 *
 * Returns:
 *  0 on success
 *  1 when the timer was active
 */
int
hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)</span>

/**
 * ktime_set - Set a ktime_t variable from a seconds/nanoseconds value
 * @secs:	seconds to set
 * @nsecs:	nanoseconds to set
 *
 * Return the ktime_t representation of the value
 */
static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)

/**
 * 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)

2 调用的方法

2.1 定义变量，在probe 里面初始化

<span style="font-size:14px;">static struct hrtimer pwm_timer;
static int  gpio_status =0;
static int count=0;
static int delaytime=0;


hrtimer_init(&pwm_timer, CLOCK_MONOTONIC,HRTIMER_MODE_REL);
 pwm_timer.function = pwm_timer_func;</span>

2 .2 模拟pwm方波

static enum hrtimer_restart pwm_timer_func(struct hrtimer *timer)
{

    gpio_set_value(gpio_num,gpio_status);   //set gpio 1/0
    gpio_status = !gpio_status;
    count--;<span style="white-space:pre">				</span>  //count control the time of constant
    if(0==count )
    	{
		 return HRTIMER_NORESTART;
    }
	else
		{
      hrtimer_start(&pwm_timer,ktime_set(0, delaytime),HRTIMER_MODE_REL);     //cycle， duty cycle = 50%
		}
   return HRTIMER_NORESTART;

}

void set_pwm(int hz,int ms)
{
    int hzTonas=0;
    hzTonas = 2*1000*1000*1000/hz;    //s to ns
     count = ms*hz/1000;             
	 delaytime=hzTonas;
    hrtimer_start(&pwm_timer,ktime_set(0, hzTonas),HRTIMER_MODE_REL);
}

3 这里只是实现占空比固定为50%的波形，需要动态设置占空比，需要修改代码。