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

unsigned char lcd_digits[10] __attribute__((progmem)) =
{0x3f, 0x06, 0x5b, 0x4f, 0x66, 0x6d, 0x7d, 0x07, 0x7f, 0x6f};

unsigned char key;
unsigned char data[4]={2,0,0,8};

ISR(TIMER0_COMP_vect)
{
	static unsigned char num=0;
	
	PORTB=(PORTB&0xf0)|1<<num;

	PORTA=pgm_read_byte(lcd_digits+data[num]);

	if(num==3)
		num=0;
	else
		num++;
}

void keyboard(void)
{
	char k;
	static unsigned char p;
	
	k=(PINB>>4)|0xf0;
	
	if(k==0xff)
	{
		p=0;
		return;
	}
	
	if(p==1)
		return;
	
	_delay_ms(10);
	
	if(k!=((PINB>>4)|0xf0))
		return;
	
	p=1;
	key=~k;
}

void menu(void)
{
	static unsigned char pos=0;
	switch(key)
	{
		case 1:
			if(pos>0)
				pos--;
		break;
		case 2:
			if(pos<3)
				pos++;
		break;
		case 4:
			if(data[pos]<9)
				data[pos]++;
		break;
		case 8:
			if(data[pos]>0)
				data[pos]--;
		break;
	}
	key=0;
}

int main(void)
{
	DDRA=0xff;
	DDRB=0x0f;
	PORTB|=0xf0;

	TCCR0=0x0c;
	OCR0=0x40;
	TIMSK|=1<<OCIE0;
	SREG|=1<<SREG_I;

	while(1)
	{
		keyboard();
		menu();
	}

	return 0;
}