kernel.c

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#define MAX_INPUT_LENGTH 100
#define true 1
#define false 0
/* Check if the compiler thinks you are targeting the wrong operating system. */
#if defined(__linux__)
#error "You are not using a cross-compiler"
#endif

/* This will only work for the 32-bit ix86 targets. */
#if !defined(__i386__)
#error "This needs to be compiled with a ix86-elf compiler"
#endif

/* Hardware text mode color constants. */
enum vga_color
{
    VGA_COLOR_BLACK = 0,
    VGA_COLOR_BLUE = 1,
    VGA_COLOR_GREEN = 2,
    VGA_COLOR_CYAN = 3,
    VGA_COLOR_RED = 4,
    VGA_COLOR_MAGENTA = 5,
    VGA_COLOR_BROWN = 6,
    VGA_COLOR_LIGHT_GREY = 7,
    VGA_COLOR_DARK_GREY = 8,
    VGA_COLOR_LIGHT_BLUE = 9,
    VGA_COLOR_LIGHT_GREEN = 10,
    VGA_COLOR_LIGHT_CYAN = 11,
    VGA_COLOR_LIGHT_RED = 12,
    VGA_COLOR_LIGHT_MAGENTA = 13,
    VGA_COLOR_LIGHT_BROWN = 14,
    VGA_COLOR_WHITE = 15,
};

char ascii_chars[128] = {
    0, 0, '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '-', '=', 
    0, 0, 'q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p', '[', ']', 
    0, 0, 'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', ';', '\'', '`', 
    0, '\\', 'z', 'x', 'c', 'v', 'b', 'n', 'm', ',', '.', '/', 0, 
    0, ' ', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

static char input_buffer[MAX_INPUT_LENGTH];
static size_t input_length = 0;
static int key_states[128] = { false }; 
static int input_ready = false;

inline unsigned char inb(unsigned int port)
{
    unsigned char ret;
    asm volatile("inb %%dx,%%al" : "=a"(ret) : "d"(port));
    return ret;
}

int strcmp(const char *s1, const char *s2) {
    while (*s1 && (*s1 == *s2)) {
        s1++;
        s2++;
    }
    return *(unsigned char *)s1 - *(unsigned char *)s2;
}

static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg)
{
    return fg | bg << 4;
}

static inline uint16_t vga_entry(unsigned char uc, uint8_t color)
{
    return (uint16_t)uc | (uint16_t)color << 8;
}

size_t strlen(const char *str)
{
    size_t len = 0;
    while (str[len])
        len++;
    return len;
}

static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;

size_t terminal_row;
size_t terminal_column;
uint8_t terminal_color;
uint16_t *terminal_buffer;

void terminal_initialize(void)
{
    terminal_row = 0;
    terminal_column = 0;
    terminal_color = vga_entry_color(VGA_COLOR_GREEN, VGA_COLOR_BLACK);
    terminal_buffer = (uint16_t *)0xB8000;
    for (size_t y = 0; y < VGA_HEIGHT; y++)
    {
        for (size_t x = 0; x < VGA_WIDTH; x++)
        {
            const size_t index = y * VGA_WIDTH + x;
            terminal_buffer[index] = vga_entry(' ', terminal_color);
        }
    }
}

void terminal_setcolor(uint8_t color)
{
    terminal_color = color;
}

void terminal_putentryat(char c, uint8_t color, size_t x, size_t y)
{
    const size_t index = y * VGA_WIDTH + x;
    terminal_buffer[index] = vga_entry(c, color);
}

void terminal_putchar(char c)
{
    if (c == '\n')
    {
        terminal_column = 0;
        terminal_row += 1;
    }
    terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
    if (++terminal_column == VGA_WIDTH)
    {
        terminal_column = 0;
        if (++terminal_row == VGA_HEIGHT)
            terminal_row = 0;
    }
}

void terminal_write(const char *data, size_t size)
{
    for (size_t i = 0; i < size; i++)
    {
        terminal_putchar(data[i]);
    }
}

void terminal_writestring(const char *data)
{
    terminal_write(data, strlen(data));
}

static void get_input_char()
{
    uint8_t scancode = inb(0x60);

    if (scancode & 0x80) {
        // Key release event
        key_states[scancode & 0x7F] = false; 
        return;

    }
    // Key press event

    if (!key_states[scancode]) { 

        key_states[scancode] = true; 
        if (scancode == 0x1C) 
        {
            terminal_writestring("\n");
            input_buffer[input_length] = '\0'; 
            if (strcmp(input_buffer, "hello") == 0) {
                terminal_writestring("HI, I am Akira OS\n");
            }
            else if (strcmp(input_buffer, "help") == 0) {
                terminal_writestring("Available commands:\n1) hello - get the greet message\n2) help - see available commands\n");
            }
            else {
                terminal_writestring("Unrecognized command, this OS is currently in development phase\n");

            }
            input_length = 0; 
        }

        else

        {

            if (scancode < 128 && input_length < MAX_INPUT_LENGTH - 1) 

            {

                char c = ascii_chars[scancode]; // Get the character from the scancode

                terminal_putchar(c); // Print the character to the terminal

                input_buffer[input_length] = c; // Store the character in the input buffer

                input_length++;

            }

        }

    }

}

void kernel_main(void)
{
    /* Initialize terminal interface */
    terminal_initialize();

    terminal_writestring("Hello, Welcome to Akira OS!\n");
    while (true){
        get_input_char();
        for(volatile int i=0; i<10000; i++){
            //we are doing this as while loop is faster 
            // hence treating single key tap as multiple
        }
    }
}