#define RCC_IOPENR  (*((volatile int*)0x40021034))
#define GPIOA_MODER  (*((volatile int*)0x50000000))
#define GPIOA_ODR    (*((volatile int*)0x50000014))

void setup() {
  RCC_IOPENR |= 0x1<<0;
  GPIOA_MODER &= ~(0x3<<26);
  GPIOA_MODER |= (0x1<<26);

}
void loop() {
  
  GPIOA_ODR |= 0x1<<13;
  delay(1000);

  GPIOA_ODR &= ~(0x1<<13);
  delay(1000);
}