#define F_CPU 1000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

static inline void initInterrupt(void)
{
	GIMSK |= (1 << PCIE);   // pin change interrupt enable
	PCMSK |= (1 << PCINT4); // pin change interrupt enabled for PCINT4
	sei();                  // enable interrupts
}

ISR(PCINT0_vect)
{
	PORTB ^= (1 << PB0) | (1 << PB2);  // toggle pins PB0 and PB2, on logical change PCINT4 pin
}

int main(void)
{
	// initializations 
	DDRB = 0x0F;         // enable PB0-PB3 as outputs
	//PORTB |= (1 << PB4); // enable pullup on pushbutton output and PCINT4 interrupt
	initInterrupt();
	
	while(1)
	{
          _delay_ms(250);
	  PORTB ^= (1 << PB1) | (1 << PB3);
	}
	
	return 0;
}