contiki-定时器etimer

/**
 * A timer.
 *
 * This structure is used for declaring a timer. The timer must be set
 * with etimer_set() before it can be used.
 *
 * \hideinitializer
 */
struct etimer {
  struct timer timer; //包含起始时刻和间隔两成员变量
  struct etimer *next; //指向下一个etimer
  struct process *p;
};

/**
 * A timer.
 *
 * This structure is used for declaring a timer. The timer must be set
 * with timer_set() before it can be used.
 *
 * \hideinitializer
 */
struct timer {
  clock_time_t start;
  clock_time_t interval;
};

static struct etimer *timerlist;

void
etimer_set(struct etimer *et, clock_time_t interval)
{
  timer_set(&et->timer, interval);//设置起始时刻和时间间隔
  add_timer(et);//将etimer添加到timerlist
}
/**
 * Set a timer.
 *
 * This function is used to set a timer for a time sometime in the
 * future. The function timer_expired() will evaluate to true after
 * the timer has expired.
 *
 * \param t A pointer to the timer
 * \param interval The interval before the timer expires.
 *
 */
void timer_set(struct timer *t, clock_time_t interval)
{
  t->interval = interval; //设置时间间隔
  t->start = clock_time(); //设置起始时刻
}
static void add_timer(struct etimer *timer)
{
  struct etimer *t;

  etimer_request_poll();//提升etimer系统进程的优先级

  if(timer->p != PROCESS_NONE) {//该etimer处理过
    for(t = timerlist; t != NULL; t = t->next) {
      if(t == timer) {
        /* Timer already on list, bail out. */
        /*此etimer已经在etimer链表中*/
        timer->p = PROCESS_CURRENT();//将现有进程赋给此etimer的进程
        update_time();
        return;
      }
    }
  }

  /* Timer not on list. */
  /*此etimer不在etimer链表中，放到etimer链表表头*/
  timer->p = PROCESS_CURRENT();
  timer->next = timerlist;
  timerlist = timer;

  update_time();
}

PROCESS_THREAD(etimer_process, ev, data)
{
  struct etimer *t, *u;
    
  PROCESS_BEGIN();

  timerlist = NULL;
  
  while(1) {
    PROCESS_YIELD();
    /*事件是否为退出事件*/
    if(ev == PROCESS_EVENT_EXITED) {
        struct process *p = data;
        
        while(timerlist != NULL && timerlist->p == p) {
            timerlist = timerlist->next;
        }
        /*如果有退出进程绑定etimer，删除所有相关的etimer*/
        if(timerlist != NULL) {
            t = timerlist;
            while(t->next != NULL) {
                if(t->next->p == p) {
                    t->next = t->next->next;
                } 
                else
                    t = t->next;
            }
        }
        continue;
    } else if(ev != PROCESS_EVENT_POLL) {
      continue;
    }

  again:
    
    u = NULL;
    /*处理所有到期的etimer*/
    for(t = timerlist; t != NULL; t = t->next) {
        if(timer_expired(&t->timer)) {
        if(process_post(t->p, PROCESS_EVENT_TIMER, t) == PROCESS_ERR_OK) {
      
            /* Reset the process ID of the event timer, to signal that the
             etimer has expired. This is later checked in the
             etimer_expired() function. */
            t->p = PROCESS_NONE;
            if(u != NULL) {
                u->next = t->next;
            } else {
                timerlist = t->next;
            }
            t->next = NULL;
            update_time();
            goto again;
            } else {
                etimer_request_poll();
            }
        }
      u = t;
    }
    
  }
  
  PROCESS_END();
}