#include <stdint.h>

// --- HARDWARE MAPPING (From Datasheet) ---
// Base Addresses
#define TEMP_RCC_BASE   0x40021000 // Reset & Clock Control
#define TEMP_GPIOA_BASE 0x50000000 // GPIO Port A
#define MY_EXTI_BASE 0x40021800
#define MY_NVIC_ISER 0xE000E100

// Register Offsets & References
// Note: We use 'volatile' so the compiler doesn't optimize the memory access away
#define TEMP_RCC_IOPENR  *(volatile uint32_t*)(TEMP_RCC_BASE + 0x34)
#define TEMP_GPIOA_MODER  *(volatile uint32_t*)(TEMP_GPIOA_BASE + 0x00)
#define TEMP_GPIOA_ODR    *(volatile uint32_t*)(TEMP_GPIOA_BASE + 0x14)
#define TEMP_GPIOA_IDR    *(volatile uint32_t*)(TEMP_GPIOA_BASE + 0x10)

#define EXTI_RTSR1    *(volatile uint32_t*)(MY_EXTI_BASE + 0x00)
#define EXTI_FTSR1    *(volatile uint32_t*)(MY_EXTI_BASE + 0x04)
#define EXTI_IMR1    *(volatile uint32_t*)(MY_EXTI_BASE + 0x80)
#define EXTI_RPR1    *(volatile uint32_t*)(MY_EXTI_BASE + 0x0C)

#define NVIC_ISER    *(volatile uint32_t*)(MY_NVIC_ISER + 0x0C)

// --- THE INTERRUPT SERVICE ROUTINE (ISR) ---
// This name is special; it's defined in the startup code/vector table.
extern "C" void EXTI0_1_IRQHandler(void) {
    // 1. Check if the interrupt came from Line 1 (Pin 1)
    if (EXTI_RPR1 & (1 << 1)) {
        TEMP_GPIOA_ODR ^= (1 << 6); // Toggle LED
        
        // 2. CLEAR the interrupt flag! 
        // In EXTI, you write a '1' to the bit to clear it (RC_W1 logic).
        EXTI_RPR1 |= (1 << 1); 
    }
}

void manual_delay(int count) {
    for (volatile int i = 0; i < count; i++);
}

int main() {
    // 1. Enable Clock for GPIOA (Bit 0 of IOPENR)
    TEMP_RCC_IOPENR |= (1 << 0);

    // 2. Configure PA5 as Output
    // MODER has 2 bits per pin. Pin 5 uses bits 10 & 11.
    // Setting to '01' makes it a General Purpose Output.
    TEMP_GPIOA_MODER &= ~(3 << 12); // Clear bits 10 and 11
    TEMP_GPIOA_MODER |=  (1 << 12); // Set bit 10 to 1

    TEMP_GPIOA_MODER &= ~(3 << 2); // Clear bits 10 and 11

    NVIC_ISER |= (1 << 5); 

    while (1) {
        // The CPU can now sleep or do other work here.
        // The LED toggle happens automatically via hardware!
    }
}