#include "STM32L1xx.h"

#define PA1 0x02 // Second bit
#define PA2 0x04 // Fourth bit
#define SWITCH1 PA1
#define SWITCH2 PA2

#define PC0 0x01
#define PC1 0x02
#define PC2 0x04
#define PC3 0x08
#define OUTPUT_PINS (PC0 | PC1 | PC2 | PC3)


void switch_setup() {
    RCC->AHBENR |= 0x01; // Enable GPIOA

    GPIOA->MODER &= ~(GPIO_MODER_MODER1 | GPIO_MODER_MODER2); // set PA[1:2] to inputs
}

void output_setup() {
    RCC->AHBENR |= 0x04;

    GPIOC->MODER &= ~(GPIO_MODER_MODER0 | GPIO_MODER_MODER1 | GPIO_MODER_MODER2 | GPIO_MODER_MODER3); // clear PC[0:3] modes
    GPIOC->MODER |= GPIO_MODER_MODER0_0 | GPIO_MODER_MODER1_0 | GPIO_MODER_MODER2_0 | GPIO_MODER_MODER3_0; // set PC[0:3] to outputs
}

void set_output(uint8_t count) {
    GPIOC->ODR = (GPIOC->ODR & ~OUTPUT_PINS) | (count & OUTPUT_PINS); // Set PC[0:3] to count
}

uint8_t read_switch1() {
    return GPIOA->IDR & SWITCH1;
}

uint8_t read_switch2() {
    return GPIOA->IDR & SWITCH2;
}

void delay() {
    // delay for roughly 500 ms
    for (int i = 0; i < 20; i++) {
        for (int j = 0; j < 10000; j++) {
            __nop();
        }
    }
}

static uint8_t count = 0;

int main() {
    switch_setup();
    output_setup();

    count = 0;

    while (1) {
        if (read_switch1()) {
            // counter is enabled

            if (read_switch2()) {
                // counting down if value is 1

                count--;
            } else {
                // counting up otherwise

                count++;
            }
        }

        set_output(count);
        delay();
    }
}