[EVAL-WSN]操作系统篇——Contiki分析之timer

dvd1478

contiki-2.5\core\sys\timer.c


1 timer结构体

struct timer {   clock_time_t start;/* 开始时间 */   clock_time_t interval;/* 时间间隔 */ };

    timer是一个独立结构，用于获取当前的时间，并计算时间间隔，本身并不能产生事件。一般用于内部进行的时间的获取，很少用于阻塞操作，使用后要手动激活任务


2、timer 代码分析

Functions
void	timer_set (struct timer *t, clock_time_t interval)
	Set a timer.
void	timer_reset (struct timer *t)
	Reset the timer with the same interval.
void	timer_restart (struct timer *t)
	Restart the timer from the current point in time.
int	timer_expired (struct timer *t)
	Check if a timer has expired.
clock_time_t	timer_remaining (struct timer *t)
	The time until the timer expires.

1. void
   
2. timer_set(struct timer *t, clock_time_t interval)
   
3. {/*用当前时间初始化start，并设置间隔interval*/
   
4.   t->interval = interval;
   
5.   t->start = clock_time();
   
6. }
   
7. 
   
8. void
   
9. timer_reset(struct timer *t)
   
10. {
    
11.   /*为什么不t->start = clock_time()？为了程序可预测性？
    
12.     造成：clock_time() 不断增加，更不是固定的周期
    
13.    */
    
14.   t->start += t->interval;
    
15. }
    
16. 
    
17. void
    
18. timer_restart(struct timer *t)
    
19. {
    
20.   t->start = clock_time();
    
21. }
    
22. 
    
23. int
    
24. timer_expired(struct timer *t)
    
25. {
    
26.   /* Note: Can not return diff >= t->interval so we add 1 to diff and return
    
27.      t->interval < diff - required to avoid an internal error in mspgcc. */
    
28.   clock_time_t diff = (clock_time() - t->start) + 1;
    
29.   return t->interval < diff;
    
30. 
    
31. }
    
32. 
    
33. clock_time_t
    
34. timer_remaining(struct timer *t)
    
35. {
    
36.   return t->start + t->interval - clock_time();
    
37. }

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