// STM32C031 LED toggle using TIM3 interrupt in Wokwi (PlatformIO/STM32CubeIDE compatible)
// Target: STM32C031F6

#include <stdint.h>

// Peripheral base addresses
#define RCC_BASE        0x40021000
#define GPIOA_BASE      0x50000000
#define TIM3_BASE       0x40000400
#define NVIC_ISER       ((volatile uint32_t *)0xE000E100)

// Register offsets/macros
#define RCC_IOPENR      (*(volatile uint32_t *)(RCC_BASE + 0x34))
#define RCC_APBENR1     (*(volatile uint32_t *)(RCC_BASE + 0x1C))
#define GPIOA_MODER     (*(volatile uint32_t *)(GPIOA_BASE + 0x00))
#define GPIOA_ODR       (*(volatile uint32_t *)(GPIOA_BASE + 0x14))

#define TIM3_CR1        (*(volatile uint32_t *)(TIM3_BASE + 0x00))
#define TIM3_DIER       (*(volatile uint32_t *)(TIM3_BASE + 0x0C))
#define TIM3_SR         (*(volatile uint32_t *)(TIM3_BASE + 0x10))
#define TIM3_PSC        (*(volatile uint32_t *)(TIM3_BASE + 0x28))
#define TIM3_ARR        (*(volatile uint32_t *)(TIM3_BASE + 0x2C))
#define TIM3_CNT        (*(volatile uint32_t *)(TIM3_BASE + 0x24))

#define LED_PIN         5
#define GPIO_PIN5       (1 << LED_PIN)

// Forward declaration for ISR
void TIM3_IRQHandler(void);

int main(void)
{
    // 1. Enable clocks for GPIOA and TIM3
    RCC_IOPENR |= (1 << 0);           // Enable GPIOA
    RCC_APBENR1 |= (1 << 1);          // Enable TIM3

    // 2. Set PA5 as output
    GPIOA_MODER &= ~(3 << (LED_PIN * 2));
    GPIOA_MODER |=  (1 << (LED_PIN * 2));

    // 3. Configure TIM3
    TIM3_CR1 = 0x0000;                // Disable timer
    TIM3_PSC = 47999;                // Prescaler for 1ms tick (48MHz / (PSC+1))
    TIM3_ARR = 499;                  // 500ms interval
    TIM3_CNT = 0;
    TIM3_DIER |= (1 << 0);           // Enable update interrupt
    TIM3_CR1 |= (1 << 0);            // Enable counter

    // 4. Enable TIM3 interrupt in NVIC (TIM3_IRQn = 29)
    NVIC_ISER[0] = (1 << 29);

    // 5. Enable global interrupts
    __asm__("cpsie i");

    while (1) {
        // Main loop does nothing
    }
}

// Interrupt handler
void TIM3_IRQHandler(void)
{
    if (TIM3_SR & (1 << 0)) {
        TIM3_SR &= ~(1 << 0);        // Clear update interrupt flag
        GPIOA_ODR ^= GPIO_PIN5;      // Toggle PA5
    }
}