Contiki Timer & Stimer 模块

一、Timer API

struct timer {
  clock_time_t start;
  clock_time_t interval;
};

CCIF void timer_set(struct timer *t, clock_time_t interval);
void timer_reset(struct timer *t);
void timer_restart(struct timer *t);
CCIF int timer_expired(struct timer *t);
clock_time_t timer_remaining(struct timer *t);

 The Contiki timer library provides functions for setting, resetting and restarting timers, and for checking if a timer has expired. An application must "manually" check if its timers have expired; this is not done automatically. The timer library use clock_time() in the clock module to get the current system time.

timer结构体，API中都是通过指针访问声明的timer。

void
timer_set(struct timer *t, clock_time_t interval)
{
  t->interval = interval;
  t->start = clock_time();
}

The API for the Contiki timer library is shown below. A timer is always initialized by a call totimer_set() which sets the timer to expire the specified delay from current time and also stores the time interval in the timer. 

int
timer_expired(struct timer *t)
{
  /* Note: Can not return diff >= t->interval so we add 1 to diff and return
     t->interval < diff - required to avoid an internal error in mspgcc. */
  clock_time_t diff = (clock_time() - t->start) + 1;
  return t->interval < diff;

}

timer_expired用于判断timer是否到期。

void
timer_reset(struct timer *t)
{
  t->start += t->interval;
}

void
timer_restart(struct timer *t)
{
  t->start = clock_time();
}

timer_reset将timer重置为从上次到期（expired）的时间开始计时。

timer_restart将timer重置为从当前时间开始计时。

The difference between these functions is that timer_reset() set the timer to expire at exactly the same time interval while timer_restart() set the timer to expire some time interval from current time, thus allowing time drift.

clock_time_t
timer_remaining(struct timer *t)
{
  return t->start + t->interval - clock_time();
}

timer_remaining用于获得离timer到期的间隔（return the time until the timer expires）

注：timer使用的是clock tick，当前时间是通过clock_time()获取的，时间变量类型都是clock_time_t

二、中断中使用timer

The timer library can safely be used from interrupts

例子如下：

 #include "sys/timer.h"
 
 static struct timer rxtimer;
 
 void init(void) {
   timer_set(&rxtimer, CLOCK_SECOND / 2);
 }
 
 interrupt(UART1RX_VECTOR)
 uart1_rx_interrupt(void)
 {
   if(timer_expired(&rxtimer)) {
     /* Timeout */
     /* ... */
   }
   timer_restart(&rxtimer);
   /* ... */
 }

三、Stimer 模块

Stimer模块和Time基本一样，唯一的区别就是，Timer用的是clock ticks，Stimer用的是Second。

struct stimer {
  unsigned long start;
  unsigned long interval;
};

void stimer_set(struct stimer *t, unsigned long interval);
void stimer_reset(struct stimer *t);
void stimer_restart(struct stimer *t);
int stimer_expired(struct stimer *t);
unsigned long stimer_remaining(struct stimer *t);
unsigned long stimer_elapsed(struct stimer *t);

void
stimer_set(struct stimer *t, unsigned long interval)
{
  t->interval = interval;
  t->start = clock_seconds();
}

如上所示，stimer结构体中的变量start和interval是unsigned long型的。

以及获取当前时间是用clock_seconds函数。

The stimer library can safely be used from interrupts.