#include "stm32c031xx.h"

/* ===== ADC bits ===== */
#define ADC_CR_ADEN_BIT        (1U << 0)
#define ADC_CR_ADSTART_BIT     (1U << 2)
#define ADC_CR_ADVREGEN_BIT    (1U << 28)
#define ADC_CR_DEEPPWD_BIT     (1U << 29)
#define ADC_CR_ADCAL_BIT       (1U << 31)

#define ADC_ISR_ADRDY_BIT      (1U << 0)
#define ADC_ISR_EOC_BIT        (1U << 2)
// ^^^ all this shit is initialization part

/* =========================================================
   Small software delays
   ========================================================= */

/* Short delay used only during ADC regulator startup */
static void small_delay(volatile uint32_t n)
{
    while (n--) {
        __asm__("nop");
    }
}

/* Approximate delay in milliseconds for visible LED blinking */
static void delay_ms(volatile uint32_t ms)
{
    volatile uint32_t i;
    while (ms--) {
        for (i = 0; i < 4000; i++) {
            __asm__("nop");
        }
    }
}

/* =========================================================
   ADC initialization: PA0 = analog input, channel 0
   ========================================================= */

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

    /* 2. Set PA0 to analog mode */
    GPIOA->MODER |= (3U << 0);

    /* 3. Enable ADC clock */
    RCC->APBENR2 |= RCC_APBENR2_ADCEN;

    /* 4. Exit deep-power-down mode */
    ADC1->CR &= ~ADC_CR_DEEPPWD_BIT;

    /* 5. Enable internal ADC voltage regulator */
    ADC1->CR |= ADC_CR_ADVREGEN_BIT;

    /* 6. Wait for regulator stabilization */
    small_delay(20000);

    /* 7. Start ADC calibration */
    ADC1->CR |= ADC_CR_ADCAL_BIT;

    /* Wait until calibration is complete */
    while (ADC1->CR & ADC_CR_ADCAL_BIT) {
    }

    /* 8. Select channel 0 (PA0) */
    ADC1->CHSELR = (1U << 0);

    /* 9. Enable ADC */
    ADC1->CR |= ADC_CR_ADEN_BIT;

    /* 10. Wait until ADC is ready */
    while (!(ADC1->ISR & ADC_ISR_ADRDY_BIT)) {
    }
}

/* =========================================================
   ADC single conversion
   ========================================================= */

static uint16_t adc_read(void)
{
    /* 11. Start one conversion by software */
    ADC1->CR |= ADC_CR_ADSTART_BIT;

    /* 12. Wait until conversion is complete */
    while (!(ADC1->ISR & ADC_ISR_EOC_BIT)) {
    }

    /* 13. Return 12-bit result: 0 to 4095 */
    return (uint16_t)ADC1->DR;
}

/* =========================================================
   LED output: PA5
   ========================================================= */

static void led_init(void)
{
    /* Enable GPIOA clock */
    RCC->IOPENR |= RCC_IOPENR_GPIOAEN;

    /* Set PA5 as general-purpose output */
    GPIOA->MODER &= ~(3U << (5U * 2U));
    GPIOA->MODER |=  (1U << (5U * 2U));
}

static void led_toggle(void)
{
    GPIOA->ODR ^= (1U << 5);
}

/* =========================================================
   Main
   ========================================================= */

int main(void)
{
    uint16_t adc_value;
    uint32_t delay_value_ms;

    adc_init();
    led_init();

    while (1)
    {
        /* Read analog value from channel 0 */
        adc_value = adc_read();

        /* Map ADC range 0..4095 to delay range 100..2000 ms */
        delay_value_ms = 10U + ((uint32_t)adc_value * 190U) / 4095U;

        /* Toggle LED using the computed delay */
        led_toggle();
        delay_ms(delay_value_ms);
    }
}