#include <stdint.h>
#include <Wire.h>
#define AS5600_AS5601_DEV_ADDRESS      0x36
#define AS5600_AS5601_REG_RAW_ANGLE    0x0C

void setup() {
  // I2C init
  Wire.begin();
  Wire.setClock(400000);

  // Read RAW_ANGLE value from encoder
  Wire.beginTransmission(AS5600_AS5601_DEV_ADDRESS);
  Wire.write(AS5600_AS5601_REG_RAW_ANGLE);
  Wire.endTransmission(false);
  Wire.requestFrom(AS5600_AS5601_DEV_ADDRESS, 2);
  uint16_t RawAngle = 0;
  RawAngle  = ((uint16_t)Wire.read() << 8) & 0x0F00;
  RawAngle |= (uint16_t)Wire.read();
  // Raw angle value (0 ~ 4095) is stored in RawAngle
}

void loop() {
}

#include <stdint.h>
#include <Wire.h>
#define AS5600_AS5601_DEV_ADDRESS       0x36
#define AS5601_REG_ABN                  0x09

volatile int32_t EncoderCount;

void Encoder_GPIO_init(void) {
  DDRD  &= ~((1 << PD2) | (1 << PD3));  // Set PD2 and PD3 as input
  EICRA = 0b00000101; // Trigger event of INT0 and INT1 : Any Logic Change
  EIMSK = 0b00000011; // Enable interrupt INT0 and INT1
  sei();              //Enable Global Interrupt
}

// Encoder "A" pin logic change interrupt callback function
ISR(INT0_vect) {
  updateEncoderCount();
}

// Encoder "B" pin logic change interrupt callback function
ISR(INT1_vect) {
  updateEncoderCount();
}

void updateEncoderCount(void) {
  const static int8_t EncoderIndexTable[] =
    {0, -1, 1, 0,  1, 0, 0, -1,  -1, 0, 0, 1,  0, 1, -1, 0};
  static uint8_t EncoderPinState_Now, EncoderPinState_Prev = 0;

  EncoderPinState_Now = (PIND >> 2) & 0x03; // Bit1 : PD3 (Encoder B), Bit0 : PD2 (Encoder A)
  EncoderCount += EncoderIndexTable[EncoderPinState_Prev << 2 | EncoderPinState_Now];
  EncoderPinState_Prev = EncoderPinState_Now;
}

void Encoder_I2C_init(void) {
  // Set AS5601 resolution 2048ppr
  Wire.beginTransmission(AS5600_AS5601_DEV_ADDRESS);
  Wire.write(AS5601_REG_ABN);
  Wire.write(0b00001000);   // ABN(3:0)
  Wire.endTransmission();
  delay(1);
}

void setup() {
  // I2C init
  Wire.begin();
  Wire.setClock(400000);

  // Peripheral init
  Encoder_I2C_init();
  Encoder_GPIO_init();
}

void loop() {
  // Angle value (0 ~ 2047) is stored in EncoderCount
}