#include <stdint.h>

/* ================= RCC ================= */
#define RCC_BASE        0x40021000UL
#define RCC_IOPENR      (*(volatile uint32_t *)(RCC_BASE + 0x2C))
#define RCC_APB1ENR     (*(volatile uint32_t *)(RCC_BASE + 0x40))
#define RCC_APB2ENR     (*(volatile uint32_t *)(RCC_BASE + 0x44))

/* ================= GPIOA ================= */
#define GPIOA_BASE      0x50000000UL
#define GPIOA_MODER     (*(volatile uint32_t *)(GPIOA_BASE + 0x00))
#define GPIOA_AFRL      (*(volatile uint32_t *)(GPIOA_BASE + 0x20))

/* ================= ADC1 ================= */
#define ADC_BASE        0x40012400UL
#define ADC_ISR         (*(volatile uint32_t *)(ADC_BASE + 0x00))
#define ADC_CR          (*(volatile uint32_t *)(ADC_BASE + 0x08))
#define ADC_CFGR1       (*(volatile uint32_t *)(ADC_BASE + 0x0C))
#define ADC_CHSELR      (*(volatile uint32_t *)(ADC_BASE + 0x28))
#define ADC_DR          (*(volatile uint32_t *)(ADC_BASE + 0x40))

/* ================= TIM2 ================= */
#define TIM2_BASE       0x40000000UL
#define TIM2_CR1        (*(volatile uint32_t *)(TIM2_BASE + 0x00))
#define TIM2_EGR        (*(volatile uint32_t *)(TIM2_BASE + 0x14))
#define TIM2_CCMR1      (*(volatile uint32_t *)(TIM2_BASE + 0x18))
#define TIM2_CCER       (*(volatile uint32_t *)(TIM2_BASE + 0x20))
#define TIM2_PSC        (*(volatile uint32_t *)(TIM2_BASE + 0x28))
#define TIM2_ARR        (*(volatile uint32_t *)(TIM2_BASE + 0x2C))
#define TIM2_CCR1       (*(volatile uint32_t *)(TIM2_BASE + 0x34))

/* ================= ADC INIT ================= */
void adc_init(void)
{
    RCC_IOPENR  |= (1 << 0);     // Enable GPIOA
    RCC_APB2ENR |= (1 << 9);     // Enable ADC

    GPIOA_MODER |= (3 << (0 * 2));   // PA0 analog mode

    ADC_CR |= (1 << 31);             // ADC calibration
    while (ADC_CR & (1 << 31));

    ADC_CR |= (1 << 0);              // Enable ADC
    while (!(ADC_ISR & (1 << 0)));   // Wait ready

    ADC_CHSELR = (1 << 0);           // Channel 0
}

/* ================= PWM INIT ================= */
void pwm_init(void)
{
    RCC_APB1ENR |= (1 << 0);          // Enable TIM2

    GPIOA_MODER &= ~(3 << (5 * 2));
    GPIOA_MODER |=  (2 << (5 * 2));   // PA5 AF mode

    GPIOA_AFRL &= ~(0xF << (5 * 4));
    GPIOA_AFRL |=  (2 << (5 * 4));    // AF2 (TIM2)

    TIM2_PSC = 79;                    // Prescaler
    TIM2_ARR = 4095;                  // 12-bit PWM

    TIM2_EGR = 1;                     // UPDATE EVENT (important)

    TIM2_CCMR1 |= (6 << 4);           // PWM mode 1
    TIM2_CCMR1 |= (1 << 3);           // Preload enable

    TIM2_CCER |= (1 << 0);            // Enable CH1
    TIM2_CR1  |= (1 << 0);            // Enable timer
}

/* ================= ADC READ ================= */
uint16_t adc_read(void)
{
    ADC_CR |= (1 << 2);               // Start conversion
    while (!(ADC_ISR & (1 << 2)));    // Wait EOC
    return (uint16_t)ADC_DR;          // 0–4095
}

/* ================= MAIN ================= */
int main(void)
{
    adc_init();
    pwm_init();

    while (1)
    {
        TIM2_CCR1 = adc_read();       // Brightness control
    }
}