#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};

unsigned mode=0;

void actual_data(unsigned int ad)
{
	data[3]=ad%10;
	data[2]=(ad/10)%10;
	data[1]=(ad/100)%10;
	data[0]=(ad/1000)%10;
}

ISR(ADC_vect)
{
	if(mode==0)
		actual_data(ADC);
}

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

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

	num++;
	num&=3;
}

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

void menu(void)
{
	static unsigned int wynik=0;

	switch(key)
	{
		case 1:
			if(mode==0)
				mode=1;
			else
				mode=0;
		break;
		case 2:
			wynik+=ADC;
		break;
		case 4:
			wynik-=ADC;
		break;
		case 8:
			wynik=0;
		break;
	}

	key=0;

	if(mode==1)
		actual_data(wynik);
}

int main(void)
{
	DDRB=0xff;
	DDRC=0x0f;
	PORTC|=0xf0;

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

	ADMUX=0x40;
	ADCSRA=0xef;

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

	return 0;
}