#define DDRB (*(volatile unsigned char *)(0x37))
#define PORTB (*(volatile unsigned char *)(0x38))

#define PIND (*(volatile unsigned char *)(0x30))
#define DDRD (*(volatile unsigned char *)(0x31))
#define PORTD (*(volatile unsigned char *)(0x32))

#define GIMSK (*(volatile unsigned char *)(0x5b))
#define SREG (*(volatile unsigned char *)(0x5f))
#define MCUCR (*(volatile unsigned char *)(0x55))

#define IRQ0 __vector_1
#define SIGNAL __attribute__ ((signal))

void IRQ0(void) SIGNAL;

int main(void) {
    int i;

    DDRB = 0xff;
    PORTB = 0xff;

    GIMSK = 0x40;
    MCUCR = 0x03;
    SREG = 0x80; 

    while(1) {}
    return 0;
}

void IRQ0(void) SIGNAL;

void IRQ0(void) {
  PORTB = ~PORTB;
}