/* Interrupt Vector Definitions*/
#define INT0      __vector_1
#define T0OVF     __vector_17
#define SIGNAL    __attribute__ ((signal))

/* AVR IO Registers Definitions */
#define PORTB  (*(volatile unsigned char *)(0x25))  /* Data register, Port B */
#define DDRB   (*(volatile unsigned char *)(0x24))  /* Data Direction Register, Port B */
#define DDRD   (*(volatile unsigned char *)(0x2A))  /* Data Direction Register, Port D */
#define PIND   (*(volatile unsigned char *)(0x29))  /* Input Pins, Port D */

#define SREG   (*(volatile unsigned char *)(0x5F))  /* Status Register */

#define EICRA  (*(volatile unsigned char *)(0x69))  /* Asynchronous External Interrupt Control Register A */
#define EIMSK  (*(volatile unsigned char *)(0x3D))  /* External Interrupt Mask Register */

#define TCNT0  (*(volatile unsigned char *)(0x46))  /* Timer/Counter0 Register */
#define TIMSK0 (*(volatile unsigned char *)(0x6E))  /* Timer/Counter0 Interrupt Mask Register */
#define TCCR0A (*(volatile unsigned char *)(0x44)) /* Timer/Counter0 Control Register A */


void INT0 (void) SIGNAL; 
void T0OVF () SIGNAL;

int main(void)
{
    DDRB  =  0xff;     // Set PORTB to output
    PORTB =  0xff;     // Turn off LEDs
    
    SREG |=  0x80;     // Enable Interrupts
    
    EIMSK =  0x01;     // Enable External Interrupt 0
    EICRA =  0x02;     // At faling edge
    
    TIMSK0 |= 0x01;    // Enable Timer0 Overflow Interrupt

    while(1);

    return 0;
}

/* IRQ 0 Interrupt Handler */
void INT0 (void) 
{
    if(EICRA == 0x03) {	// If IRQ0 is rising edge (button released)
        EICRA  = 0x02;	// Set IRQ0 to falling edge
        PORTB  = 0xff;  // Turn off LEDs
        TCCR0A &= ~0x07;	// Disable TIMER0 
    } else {			// IRQ1 is falling edge (button pressed)
        EICRA  = 0x03;  // Set IRQ0 to rising edge
        TCNT0  = 0x00;  // Clear timer counter
        TCCR0A |= 0x05;	// Start TIMER0 @ CLK/256
    }
}

/* Timer1 Interrupt Handler */
void T0OVF () {
    PORTB = 0x00;
}