Clock.c

/*
 * Clock.c
 *
 * Created: 5/25/2016 1:01:13 AM
 * Author : andrey
 */ 
#define F_CPU 1000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

#define TRUE 1
#define FALSE 0
typedef unsigned char bool;
#define Ndigits 4			// only work with power of two

static unsigned char mode = 0;
volatile unsigned char digits[4];
const unsigned char seg7[10] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};
volatile unsigned char button_disable;
static unsigned char index = 0;

void setupTimer1() {
	//setup TIMER1
	TCCR1A |= 0;	//CTC mode
	TCCR1B |= (1<<WGM12)|(1<<CS12)|(1<<CS10);	// prescaler 1024
		
	OCR1A = F_CPU/1024;		// compare value of CTC mode
	TIMSK|=(1<<OCIE1A);		//enable interrupt
}

void setupTimer0() {
	TCCR0 |= (1 << CS01);
	TCNT0 = 0;
	TIMSK |= (1 << TOIE0);
}

bool increaseMinute() {
	digits[3] ++;
	if (digits[3] > 9) {
		digits[3] = 0;
		digits[2] ++;
		if (digits[2] == 6) {
			digits[2] = 0;
			return TRUE;
		}
	}
	return FALSE;
}

void increaseHour() {
	digits[3] = 0;
	digits[2] = 0;
	digits[1] ++;
	if (digits[1] > 9) {
		digits[1] = 0;
		digits[0] ++;
	}
	if ((digits[0]*10 + digits[1]) > 12) {
		digits[0] = 0;
		digits[1] = 1;
	}
}

int main(void)
{
	PORTB = 1 << 2;		//pull up activated at PB2
	PORTD = 0b00001100;
	GICR = (1<<INT0)|(1<<INT1)|(1<<INT2);	//external interrupt 0, 1 and 2
	
	setupTimer1();
	setupTimer0();

	sei();
	
	digits[0] = 1;
	digits[1] = 1;
	digits[2] = 5;
	digits[3] = 5;
    
	DDRC = 0xFF;
	DDRA = 0xFF;		// Port A for the multiplex
	
	mode = 0;
	index = 0;
	while(1) {};
	return 0;
}

ISR(TIMER0_OVF_vect) {
	if (button_disable > 0)
		button_disable --;
	index ++;
	index &= (Ndigits - 1);
	PORTA = 1 << index;
	PORTC = seg7[digits[index]];
}

ISR(INT0_vect) {
	if (button_disable == 0) {
		if (mode == 1) {
			increaseHour();
		}
		button_disable = 1;
	}
}

ISR(INT1_vect) {
	if (button_disable == 0) {
		if (mode == 1) {
			increaseMinute();
		}
		button_disable = 1;
	}
}

ISR(INT2_vect) {
	mode ++;
	mode &= 1;
}

ISR(TIMER1_COMPA_vect) {
	if (mode == 0) {
		if (increaseMinute()) {
			increaseHour();
		}
	}
}