main.c

/*
 * Preemptive Scheduler
 *
 * Created: 17/5/2016 07:17:40 AM
 * Author : Dean McNiven
 */

#include <avr/io.h>
#include <avr/interrupt.h>
#include "stdio.h"

#ifdef GREEDY_TASK
    #define F_CPU 16000000UL
    #include <util/delay.h>
#endif

#include "preempt_sched.h"
#include "display.h"

void setup_timer(void);
void reset_timer_interrupt(void);

static uint8_t task_one_stack[PROCESS_STACK_SIZE];
void task_one(void);

static uint8_t task_two_stack[PROCESS_STACK_SIZE];
void task_two(void);

static uint8_t task_three_stack[PROCESS_STACK_SIZE];
void task_three(void);

int main()
{
    cli();
    setup_timer();
    setup_display();

    add_process(&task_three, &task_three_stack[PROCESS_STACK_SIZE - 1]);
    add_process(&task_two, &task_two_stack[PROCESS_STACK_SIZE - 1]);
    add_process(&task_one, &task_one_stack[PROCESS_STACK_SIZE - 1]);
    scheduler_init();

    reset_timer_interrupt();
    sei();

    schedule();

    while (1) { /* Should never be here */ }
    return 0;
}

void setup_timer()
{
    //Setup Ticks generation
    ASSR = 0x00;    //Timer2: Internal Clock
    TCCR2A = 0x02;  //CTC Mode
    TCCR2B = 0x07;  //Prescale: 1024
    OCR2A = 0x9C;   //Count: 156 (~10ms)
    TIMSK2 = 0x02;  //Enable Compare Interrupt
}

void reset_timer_interrupt()
{
    TIFR2 = 0x02;
}

ISR(TIMER2_COMPA_vect)
{
    uint8_t sreg = SREG;
    restore_processes();
    SREG = sreg;

    schedule();
}

void task_one()
{
    while (1) {
        LED = (LED ^ LED1_MASK);

        sleep(25);
    }
}

void task_two()
{
    while (1) {
        LED = (LED ^ LED0_MASK);

#ifdef GREEDY_TASK
        _delay_ms(1000);
#else
        sleep(100);
#endif
    }
}

void task_three()
{
    uint8_t count_h = 0;
    uint8_t count_l = 0;

    while (1) {
        BCD = (count_h << BCD_OFFSET) | (1 << BCD_L_MSD);
        BCD = (count_l << BCD_OFFSET) | (1 << BCD_L_LSD);
        BCD = BCD_BLANK;

        count_l++;
        if (count_l >= 10) {
            count_l = 0;
            count_h++;
        }
        if (count_h >= 10) count_h = 0;

        sleep(50);
    }
}