#include <stdint.h>

// Register memory addresses for STM32C0 series
#define RCC_IOPENR    (*(volatile uint32_t *)(0x40021034)) // Clock Enable: Wakes up Port A so it can receive power
#define GPIOA_MODER   (*(volatile uint32_t *)(0x50000000)) // Mode Register: Configures pins as INPUT or OUTPUT
#define GPIOA_PUPDR   (*(volatile uint32_t *)(0x5000000C)) // Resistor Register: Manages internal Pull-Up / Pull-Down settings
#define GPIOA_IDR     (*(volatile uint32_t *)(0x50000010)) // Input Register: Reads live HIGH (3.3V) or LOW (0V) signals from pins
#define GPIOA_ODR     (*(volatile uint32_t *)(0x50000014)) // Output Register: Sends HIGH (3.3V) or LOW (0V) power commands to pins


// Simple delay function that pauses execution by wasting processor time
void delay(volatile uint32_t count) { 
    
    // 'volatile' prevents the compiler from deleting this loop to optimize speed.
    // 'while(count--)' runs a loop, subtracting 1 from 'count' until it hits 0.
    while(count--) { 
        
        // '__asm("nop")' is a raw Assembly command meaning "No Operation".
        // It forces the CPU core to waste exactly 1 clock cycle doing absolutely nothing.
        __asm("nop"); 
    }
}


int main(void) {
    // 1. Enable clock for GPIOA port
    RCC_IOPENR |= (1 << 0);
    
    // 2. Configure PA0 (A0) as Output
    GPIOA_MODER &= ~(3 << 0); 
    GPIOA_MODER |=  (1 << 0); 

    // 3. Configure PA1 (A1) as Input
    GPIOA_MODER &= ~(3 << 2); 

    // 4. Clear internal pull-up/down resistors (Not needed because you have an external one!)
    GPIOA_PUPDR &= ~(3 << 2); 

    while (1) {
        // 5. FIXED: Added '!' to check if PA1 is LOW (0V / Pressed)
        if (!(GPIOA_IDR & (1 << 1))) {
            GPIOA_ODR ^= (1 << 0); // Toggle PA0 to blink the blue LED
            delay(200000);        // Blink pace delay
        } else {
            GPIOA_ODR &= ~(1 << 0); // Keep LED completely off when not pressed
        }
    }
}