#include <avr/io.h>

#define SET(REGISTER, BIT)		REGISTER |= 1 << BIT
#define CLEAR(REGISTER, BIT)	REGISTER &= ~(1 << BIT)
#define TEST(REGISTER, BIT)		REGISTER & 1 << BIT
#define TOGGLE(REGISTER, BIT)	REGISTER ^= 1 << BIT

#define D1 0
#define D2 1
#define D3 2
#define D4 4

// 14.2 : registers :
// DDRx : (Data Direction Register) Controls whether each pin is an input or output
//      - 1 = output (pull-up off)
//      - 0 = input
// PORTx : (Port Data Register)
//      if DDRx = 1 (output mode) : Controls the output state of a pin when it's configured as an output
//      - 1 = HIGH (5V?) (VCC)
//      - 0 = LOW (0V) (GND)
//      if DDRx = 0 (input mode) : Controls the internal pull-up resistor when the pin is an input
//      - 1 = pull-up on
//      - 0 = pull-up off (pin floats)
// PINx : (Pin Input Register) Reads the current logical state of a pin
// 		Reflects the actual voltage on the pin
// 		Special feature: Writing 1 to PINxn toggles the corresponding PORTxn bit (regardless of DDRx)

// turns on led 1 with only AVR registers (DDRX , PORTX, PINX)
int main()
{
	// turns on led 1
    SET(DDRB, D1);          // make PB0 as OUTPUT (pullup is off)
    SET(PORTB, D1);         // make PB0 as HIGH (LED turns ON)

    return 0;
}