#include "stm32f10x.h"

uint8_t seg_code[10] = {
    0x3F, // 0
    0x06, // 1
    0x5B, // 2
    0x4F, // 3
    0x66, // 4
    0x6D, // 5
    0x7D, // 6
    0x07, // 7
    0x7F, // 8
    0x6F  // 9
};

void delay_ms(uint32_t ms) {
    for (uint32_t i = 0; i < ms * 8000; i++);
}

void GPIO_Config(void) {
    RCC->APB2ENR |= RCC_APB2ENR_IOPAEN | RCC_APB2ENR_IOPBEN | RCC_APB2ENR_IOPCEN;

    // PORTA as output for segments
    GPIOA->CRL = 0x33333333; // PA0–PA7 output push-pull 50MHz

    // PORTB as input (data source)
    GPIOB->CRL = 0x44444444; // PB0–PB7 input floating

    // PORTC pins 0–2 as output (digit select)
    GPIOC->CRL &= ~0x00000FFF;
    GPIOC->CRL |=  0x00000333;
}

void display_digit(uint8_t digit, uint8_t pos) {
    // Turn off all digits
    GPIOC->ODR &= ~(0x07);

    // Output segment pattern
    GPIOA->ODR = seg_code[digit];

    // Enable current position
    GPIOC->ODR |= (1 << pos);

    delay_ms(5); // small multiplexing delay
}

int main(void) {
    uint8_t value, hundreds, tens, ones;

    GPIO_Config();

    while (1) {
        value = GPIOB->IDR & 0xFF; // read byte from PORTB

        hundreds = value / 100;
        tens = (value % 100) / 10;
        ones = value % 10;

        // multiplex display
        display_digit(hundreds, 0);
        display_digit(tens, 1);
        display_digit(ones, 2);
    }
}