#include <stm32f1xx.h>

int main(int argc, char *argv[])
{
    RCC->APB2ENR |= RCC_APB2ENR_IOPCEN;
    GPIOC->CRH &= ~(GPIO_CRH_MODE13_Msk | GPIO_CRH_CNF13_Msk);
    GPIOC->CRH |= (GPIO_CRH_MODE13_0);

    while (1) {
        for (volatile int i = 0; i < 100000; i++)
            ;

        GPIOC->ODR ^= (1 << 13);
    }
}