#include "stm32f1xx.h"

int main(void)
{
    /* 1. Enable GPIOC clock */
    RCC->APB2ENR |= (1U << 4);

    /* 2. Configure PC13 as general-purpose push-pull output */
    GPIOC->CRH &= ~(0xFU << 20);
    GPIOC->CRH |=  (0x2U << 20);

    /* 3. Enable TIM2 clock */
    RCC->APB1ENR |= (1U << 0);

    /* 4. Configure TIM2 for 100 ms */
    TIM2->PSC = 7199;
    TIM2->ARR = 999;
    TIM2->CNT = 0;

    /* Generate an update event to load timer settings */
    TIM2->EGR = 1U;

    /* Clear update flag */
    TIM2->SR &= ~1U;

    /* 5. Start TIM2 */
    TIM2->CR1 |= 1U;

    while (1)
    {
        /* Check timer update flag */
        if (TIM2->SR & 1U)
        {
            /* Clear flag */
            TIM2->SR &= ~1U;

            /* Toggle PC13 */
            GPIOC->ODR ^= (1U << 13);
        }
    }
}