Timer library

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Detailed Description

The Contiki kernel does not provide support for timed events. Rather, an application that wants to use timers needs to explicitly use the timer library.

The 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.

A timer is declared as a struct timer and all access to the timer is made by a pointer to the declared timer.

Example:

 static struct timer periodic;

 LOADER_INIT_FUNC(example_init, arg) {
   timer_set(&periodic, CLOCK_SECOND);
 }
 
 EK_POLLHANDLER(pollhandler) {
   if(timer_expired(&periodic)) {
     timer_restart(&periodic);
     do_periodic_stuff();
   }
 }

Note:

The timer library uses the Clock library to measure time. Intervals should be specified in the format used by the clock library.

See also:

Clock library

Files
file	timer.h
	Timer library header file.
file	timer.c
	Timer library implementation.
Data Structures
struct	timer
	A timer. More...
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.

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Function Documentation

int timer_expired (  struct timer *  t  )

Check if a timer has expired. This function tests if a timer has expired and returns true or false depending on its status. Parameters: t  A pointer to the timer Returns: Non-zero if the timer has expired, zero otherwise.

void timer_reset (  struct timer *  t  )

Reset the timer with the same interval. This function resets the timer with the same interval that was given to the timer_set() function. The start point of the interval is the exact time that the timer last expired. Therefore, this function will cause the timer to be stable over time, unlike the timer_rester() function. Parameters: t  A pointer to the timer. See also: timer_restart()

void timer_restart (  struct timer *  t  )

Restart the timer from the current point in time. This function restarts a timer with the same interval that was given to the timer_set() function. The timer will start at the current time. Note: A periodic timer will drift if this function is used to reset it. For preioric timers, use the timer_reset() function instead. Parameters: t  A pointer to the timer. See also: timer_reset()

void timer_set (  struct timer *  t, clock_time_t  interval )

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. Parameters: t  A pointer to the timer interval  The interval before the timer expires.

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