void setup() {
  RCC->AHBENR |= (1 << 0); //0 -> GPIOA
  RCC->AHBENR |= (1 << 1); //1 -> GPIOB
  RCC->AHBENR |= (1 << 2); //2 -> GPIOC

  GPIOB->MODER = 0x00000000;
  GPIOA->MODER = 0x55555555;
  GPIOB->PUPDR = 0xAAAAAAAA;
}

int i = 1;
void loop() {
  //GPIOA->ODR = GPIOB->IDR;
  if (GPIOB->IDR % 2 == 0) {
    GPIOA->ODR = i;
    i *= 2;
    if (i > 128) {
      i = 1;
    }
  } else {
    GPIOA->ODR = i;
    i /= 2;
    if (i < 1) {
      i = 128;
    }
  }
  delay(100);
}

void hinher() {
  boolean richtung = true;
  if (richtung) {
    GPIOA->ODR = i;
    i *= 2;
    if (i > 128) {
      i = 1;
    }
  } else {
    GPIOA->ODR = i;
    i /= 2;
    if (i < 1) {
      i = 128;
    }
  }
  delay(100);
}