#include "stm32l031xx.h"


volatile uint16_t adc_value;


void tim2_init_1khz(void){
  RCC->APB1ENR |= RCC_APB1ENR_TIM2EN;

  TIM2->CR1 = 0;

  TIM2->PSC = 15;
  TIM2->ARR = 999;

  TIM2->CNT = 0;


  TIM2->CR1 &= ~(7U << 4);
  TIM2->CR1 |= (2U << 4);

  TIM2->EGR = TIM_EGR_UG;

  TIM2->SR &= ~TIM_SR_UIF;

  /* Enable timer */
  TIM2->CR1 |= TIM_CR1_CEN;
}

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

    /* 2. Enable ADC clock */
    RCC->APB2ENR |= RCC_APB2ENR_ADCEN;

    /* 3. Configure PA0 as analog input */
    GPIOA->MODER &= ~(3U << (2U * 0));
    GPIOA->MODER |=  (3U << (2U * 0));

    /* Disable pull-up/pull-down */
    GPIOA->PUPDR &= ~(3U << (2U * 0));

    /* 4. Ensure ADC is disabled before calibration */
    ADC1->CR &= ~ADC_CR_ADEN;

    /* 5. Start ADC calibration */
    ADC1->CR |= ADC_CR_ADCAL;

    /* Wait for calibration to complete */
    while (ADC1->CR & ADC_CR_ADCAL)
    {
    }

    /* 6. Select ADC channel 0 */
    ADC1->CHSELR = (1U << 0);

    /*
    * Configure ADC external trigger:
    *
    * EXTSEL = 010 -> TIM2_TRGO
    * EXTEN  = 01  -> Rising edge
    * CONT   = 0   -> Single conversion per trigger
    */

    ADC1->CFGR1 &= ~(ADC_CFGR1_EXTSEL |
                    ADC_CFGR1_EXTEN  |
                    ADC_CFGR1_CONT);

    ADC1->CFGR1 |= ADC_CFGR1_EXTSEL_1 |
                  ADC_CFGR1_EXTEN_0;


    /* 7. Configure sampling time */
    ADC1->SMPR = 7U;

    /* 8. Enable ADC */
    ADC1->CR |= ADC_CR_ADEN;

    /* Wait until ADC is ready */
    while (!(ADC1->ISR & ADC_ISR_ADRDY))
    {
    }

    /* Clear ADC ready flag */
    ADC1->ISR |= ADC_ISR_ADRDY;
}


uint16_t ADC_Read(void)
{
    /* Start conversion */
    ADC1->CR |= ADC_CR_ADSTART;

    /* Wait for conversion to complete */
    while (!(ADC1->ISR & ADC_ISR_EOC))
    {
    }

    /* Read converted result */
    return (uint16_t)ADC1->DR;
}


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  ADC_Init();

  tim2_init_1khz();

  Serial.println("ADC sampling at 1 kHz");
}

void loop() {
  if (ADC1->ISR & ADC_ISR_EOC)
    {
        adc_value = ADC1->DR;
    }

    /*
     * Display the most recent sample at 20 Hz.
     * We do not print every 1 kHz conversion.
     */
  static uint32_t last_print = 0;

  if (millis() - last_print >= 50)
  {
      last_print = millis();

      Serial.print("ADC: ");
      Serial.println(adc_value);
  }
}