//FreeRTOS library:
#include <Arduino_FreeRTOS.h>
//Variables for 74HC595 shift register:
int latchPin = 5;	//Latch pin of 74HC595 is connected to Digital pin 5
int clockPin = 6;	//Clock pin of 74HC595 is connected to Digital pin 6
int dataPin = 4;	//Data pin of 74HC595 is connected to Digital pin 4
byte leds = 0;		//Variable to hold the pattern of which LEDs are currently turned on or off

void setup(){
  //Set all the pins of 74HC595 as OUTPUT:
  pinMode(latchPin, OUTPUT);  pinMode(dataPin, OUTPUT);  pinMode(clockPin, OUTPUT);
  //Task initalization:
  xTaskCreate(LEDs, "74HC595", 100, NULL, 0, NULL);
}

static void LEDs(void* pvParameters){
  //Initially turns all the LEDs off, by giving the variable 'leds' the value 0
  leds = 0;  updateShiftRegister();  vTaskDelay(500 / portTICK_PERIOD_MS);
  for (int i = 0; i < 2; i++){
    bitSet(leds, i);    //Set the bit that controls that LED in the variable 'leds'
    updateShiftRegister();
    vTaskDelay(500 / portTICK_PERIOD_MS);
  }
}

/* „updateShiftRegister()” - This function sets the latchPin to low,
 * then calls the Arduino function 'shiftOut' to
 * shift out contents of variable 'leds' in the shift register
 * before putting the 'latchPin' high again. */
void updateShiftRegister(){
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, leds);
  digitalWrite(latchPin, HIGH);
}

//No need for 'loop' function when FreeRTOS is used!
void loop(){}