Chapter 5. Timer

The Timer module provides a mechanism to execute a piece of code after a specified timeout period. This can be done through hardware timers. But hardware timers are limited and scarce resource in micro-controllers. The Timer module provides theoretically infinite number of software timers using only one hardware timer.

The Timer functions are declared in timer.h. An opaque structure timer_t to store the timer’s internal state. The following example blinks LED1 with a period of 2 seconds, and turns on LED2 after a period of 10 seconds.

Listing 5.1. Timer Demonstration

#include <stdlib.h>
#include <board.h>
#include <timer.h>

timer_t timer1;
timer_t timer2;

void blink1(timer_t *timer) __reentrant
{
        static bool state;

        gpio_set_pin(LED1_GPIO, state);
        state = !state;

        /* For periodic timer, reschedule to a later time. */
        timer_setup(timer, 2000);
}

void blink2(timer_t *timer) __reentrant
{
        gpio_set_pin(LED2_GPIO, 0);
        /* For one shot timer, unregister callback. */
        timer_setcb(timer, NULL);
}

int main()
{
        board_init();
        timer_init();

        gpio_init();
        gpio_enable_pin(LED1_GPIO);
        gpio_direction_output(LED1_GPIO, OFF);

        timer_setup(&timer1, 2000);  /* Periodic, 2s period */
        timer_setcb(&timer1, blink1);

        timer_setup(&timer2, 10000); /* One shot, after 10s */
        timer_setcb(&timer2, blink2);

        event_poll();
        return 0;
}


irq_disable		timer_init