#include "stm32c031xx.h"
#include <stdint.h>
#define DEBUG_MODE
volatile uint32_t button_pressed = 0;
// ============================================================
// EXTI0_1 IRQ Handler
// STM32C031: EXTI Line 0 và Line 1 dùng chung IRQ
// ============================================================
void EXTI01_IRQHandler(void)
{
  //Set led pin high
  //GPIOA->ODR ^= (1U << 5);
  //Signal to turn on led
  button_pressed = 1U;
}


// ============================================================
// Setup
// ============================================================
void setup()
{
    // --------------------------------------------------------
    // 1. Enable clock GPIOA
    // --------------------------------------------------------
    RCC->IOPENR |= RCC_IOPENR_GPIOAEN;

    // Enable clock SYSCFG
    RCC->APBENR2 |= RCC_APBENR2_SYSCFGEN;


    // --------------------------------------------------------
    // 2. PA5 = Output
    // --------------------------------------------------------

    // Clear MODER5[1:0]
    GPIOA->MODER &= ~(3U << (5U * 2U));

    // 01 = General purpose output
    GPIOA->MODER |= (1U << (5U * 2U));


    // --------------------------------------------------------
    // 3. PA0 = Input
    // --------------------------------------------------------

    // 00 = Input
    GPIOA->MODER &= ~(3U << (0U * 2U));


    // --------------------------------------------------------
    // 4. PA0 Pull-down
    // --------------------------------------------------------
    // Clear PUPDR0[1:0]
    GPIOA->PUPDR &= ~(3U << (0U * 2U));

    // 10 = Pull-down
    GPIOA->PUPDR |= (2U << (0U * 2U));

    // --------------------------------------------------------
    // 5. Configure EXTI0 source = PA0
    // --------------------------------------------------------

    // EXTICR[0] controls EXTI0..EXTI3
    //
    // EXTICR1:
    // bits [3:0] = EXTI0 source
    //
    // 0000 = Port A
    EXTI->EXTICR[0] &= ~(0x0FU << 0U);
    EXTI->EXTICR[0] |=  (0x00U << 0U);


    // --------------------------------------------------------
    // 6. Configure Rising Edge
    // --------------------------------------------------------

    // Disable Falling Edge
    EXTI->FTSR1 &= ~EXTI_FTSR1_FT0;

    // Enable Rising Edge
    EXTI->RTSR1 |= EXTI_RTSR1_RT0;


    // --------------------------------------------------------
    // 7. Unmask EXTI Line 0
    // --------------------------------------------------------

    EXTI->IMR1 |= EXTI_IMR1_IM0;


    // --------------------------------------------------------
    // 8. Clear any pending flag before enabling NVIC
    // --------------------------------------------------------

    EXTI->RPR1 = EXTI_RPR1_RPIF0;
    EXTI->FPR1 = EXTI_FPR1_FPIF0;


    // --------------------------------------------------------
    // 9. Configure NVIC
    // --------------------------------------------------------
    __disable_irq();

    __enable_irq();
    //NVIC->ISER[0] = (1U << 7);
    //NVIC_SetPriority(EXTI0_1_IRQn, 2);
    //NVIC_EnableIRQ(EXTI0_1_IRQn);
    attachInterrupt(digitalPinToInterrupt(A0), EXTI01_IRQHandler, RISING);

    // LED initially OFF
    GPIOA->ODR &= ~GPIO_ODR_OD5;
    Serial.begin(115200);
}


// ============================================================
// Loop
// ============================================================
static uint32_t last_pressed = 0;
void loop()
{
    // CPU sleep until interrupt occurs
    //__WFI();
    //Debounce button logic

    if (button_pressed){
      button_pressed = 0U;
      uint32_t timeNow = millis();
      if (timeNow - last_pressed >= 140U){
        #ifdef DEBUG_MODE
        if (last_pressed == 0){
          Serial.println("First pressed time: ");
          Serial.println(timeNow);       
        } else {
          Serial.println("time between 2 presses: ");
          Serial.println(timeNow - last_pressed);
        }
        #endif
        GPIOA->ODR ^= (1U << 5);
        last_pressed = timeNow;
      }
    }

}


//Bare metal EXTI_Handler
/*
void EXTI0_1_IRQHandler(void)
{
    // Kiểm tra cờ Rising Edge của EXTI Line 0
    if (EXTI->RPR1 & EXTI_RPR1_RPIF0)
    {
        // Đảo trạng thái LED PA5
        GPIOA->ODR ^= GPIO_ODR_OD5;

        // Xóa cờ Rising Pending Flag
        // W1C: Write 1 to Clear
        EXTI->RPR1 = EXTI_RPR1_RPIF0;
    }

    // Nếu vô tình có cờ Falling Edge
    if (EXTI->FPR1 & EXTI_FPR1_FPIF0)
    {
        // Xóa cờ Falling Pending Flag
        EXTI->FPR1 = EXTI_FPR1_FPIF0;
    }
}
*/