// https://arbaranwal.github.io/tutorial/2017/06/23/atmega328-register-reference.html
// https://playground.arduino.cc/Code/BitMath/
// https://stackoverflow.com/questions/13704076/passing-a-port-as-a-variable-avr

#include <avr/io.h>

volatile uint8_t* LED_DDR;
volatile uint8_t* LED_PORT;

void LED(volatile uint8_t* port, uint8_t pin) {
  LED_DDR  = (port - 1);
  LED_PORT = port;
    
  // the variable port is a pointer that means the address of PORTD ==> (&PORTD)
  //  (port -1) sets DDRx-address (is one address below PORT address)
  // *(port -1) the "*" points to the contents of DDRx
  // (1 << pin) setting the bit of a certain pin
  // *(port -1) |= (1 << pin);
  // *(LED_PORT -1) |= (1 << pin);
  *LED_DDR |= (1 << pin);  
       
  // set the pin high, pin is usual like "PD5"
  // *port |= (1<< pin);
  *LED_PORT |= (1<< pin);
}

int main(void) {
  // calling the function LED with option PORT-address &PORTD
  //                          with option pin PD4
  LED(&PORTD, PD5);

   
  while (1) {
  }
}