#include <avr/io.h>
#include <avr/interrupt.h>
//Oscilador externo. 

//tambien tengo que hacer el de intensidad del led.

void io_init() {
	DDRB = (1<<PB7);
	PORTB = (1<<PB7);
}

//esta inicializacion es para utilizar el oscilador externo, con este oscilador se puede hacer 1-8 segundos sin problemas. 
void timer_init () {
	
//1. Disable the Timer/Counter2 interrupts by clearing OCIE2x and TOIE2.
	TIMSK2 = 0;
//2. Select clock source by setting AS2 as appropriate.
	ASSR = (1<<AS2);
//3. Write new values to TCNT2, OCR2x, and TCCR2x.
	TCNT2 = 0;
	TCCR2A = (1<<WGM21);
	TCCR2B = (7<<CS20);
	OCR2A = 32 - 1;
	
//4. To switch to asynchronous operation: Wait for TCN2UB, OCR2xUB, and TCR2xUB.
	while (ASSR&0x1F) ;
//5. Clear the Timer/Counter2 Interrupt Flags.
	TIFR2 = 7;
//6. Enable interrupts, if needed.
	TIMSK2 = (1<<OCIE2A);
	sei();
}

ISR (TIMER2_COMPA_vect) {
	PORTB = ((~PINB) & (1<<PB7));
}

void main () {
	io_init();
	timer_init();
	while (1) ;
}