demo_timers.c

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <stdint.h>

#include "gpio.h"
#include "timers.h"

#define PIN_LED 28
#define my_timer TIMER0

void setup_led()
{
    // configure LED pin as output
    gpio_config_output(PIN_LED);
}

void setup_timer()
{
    // reset timer
    TIMER_TASK_STOP(my_timer)  = 1;
    TIMER_TASK_CLEAR(my_timer) = 1;

    // configure 16MHz crystal frequency as clock source
    CLOCK_XTALFREQ = 0xFF;

    // start high frequency clock
    // (is that necessary?)
    CLOCK_TASK_HFCLKSTART = 1;
    while (!CLOCK_EVENT_HFCLKSTARTED)
        asm("nop");

    // configure timer frequency
    TIMER_PRESCALER(my_timer) = 9;

    // configure timer mode
//    TIMER_MODE(my_timer)       = TIMER_MODE_TIMER;
//    TIMER_BITMODE(my_timer)    = TIMER_BITMODE_32BIT;

    // configure timer interrupt
    TIMER_CC(my_timer)[0] = 0xffffffff;
    TIMER_INTENSET(my_timer)  |= TIMER_INTERRUPT_UPON_COMPARE(0);
    interrupt_enable(TIMER0_INTERRUPT);

    // configure shortcut
    /*
    TIMER_SHORTCUTS(my_timer) =
            TIMER_SHORTCUT_COMPARE_CLEAR(0)
          | TIMER_SHORTCUT_COMPARE_STOP(0);
    */
}

bool led_on = false;
uint32_t counter = 0;

void TIMER0_Handler()
{
    TIMER_TASK_STOP(my_timer) = 1;
    TIMER_TASK_CLEAR(my_timer) = 1;
    TIMER_EVENT_COMPARE(my_timer)[0] = 0;

    counter++;
    if (counter >= 50000)
    {
        counter = 0;

        if (led_on)
        {
            GPIO_OUT &= ~(1 << PIN_LED);
            led_on = false;
        }
        else
        {
            GPIO_OUT |= 1 << PIN_LED;
            led_on = true;
        }
    }

    // restart timer
//    TIMER_CC(my_timer)[0] = 0x10000;
    TIMER_TASK_START(my_timer) = 1;
}

void main()
{
    setup_led();
    setup_timer();

    // enable timer
    TIMER_TASK_START(my_timer) = 1;

    while (true)
    {
        asm("wfi");
    }
}