path: root/src/kernel.c

/* Copyright (c) 2026 Arslaan Pathan
This software is licensed under the ARPL. See LICENSE for details. */

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include "font8x8_basic.h"

#define KB_DATA_PORT 0x60
#define KB_STATUS_PORT 0x64
#define KB_OBF 0x01

/* check if compiler thinks we are targeting incorrect OS. */
#if defined(__linux__)
#error "you are not using a cross-compiler, this is bad. use an elf cross-compiler for ix86 targets, for example, i386-elf-gcc"
#endif

/* OS only works on 32bit ix86 */
#if !defined(__i386__)
#error "this operating system is only supported on ix86 targets. use an elf cross-compiler for ix86 targets, for example, i386-elf-gcc"
#endif

static int term_col = 0;
static int term_row = 0;
static uint32_t *g_framebuffer = NULL;
static uint32_t g_width = 0;
static uint32_t g_height = 0;
static uint32_t g_default_color = 0xFFFFFF;
static bool kbd_shifted = false;

/* what in the dark magic? ok just dont touch one can hope */
struct multiboot_info {
	uint32_t flags;
	uint32_t mem_lower;
	uint32_t mem_upper;
	uint32_t boot_device;
	uint32_t cmdline;
	uint32_t mods_count;
	uint32_t mods_addr;
	uint32_t syms[4];
	uint32_t mmap_length;
	uint32_t mmap_addr;
	uint32_t drives_length;
	uint32_t drives_addr;
	uint32_t config_table;
	uint32_t boot_loader_name;
	uint32_t apm_table;
	uint32_t vbe_control_info;
	uint32_t vbe_mode_info;
	uint16_t vbe_mode;
	uint16_t vbe_interface_seg;
	uint16_t vbe_interface_off;
	uint16_t vbe_interface_len;
	uint64_t framebuffer_addr;
	uint32_t framebuffer_pitch;
	uint32_t framebuffer_width;
	uint32_t framebuffer_height;
	uint8_t  framebuffer_bpp;
	uint8_t  framebuffer_type;
	uint8_t  color_info[6];
} __attribute__((packed));

static const char scancode_to_ascii[128] __attribute__((section(".text"))) = {
	[0x29] = '`',
	[0x02] = '1',
	[0x03] = '2',
	[0x04] = '3',
	[0x05] = '4',
	[0x06] = '5',
	[0x07] = '6',
	[0x08] = '7',
	[0x09] = '8',
	[0x0A] = '9',
	[0x0B] = '0',
	[0x0C] = '-',
	[0x0D] = '=',
	[0x0E] = '\b',

	[0x10] = 'q',
	[0x11] = 'w',
	[0x12] = 'e',
	[0x13] = 'r',
	[0x14] = 't',
	[0x15] = 'y',
	[0x16] = 'u',
	[0x17] = 'i',
	[0x18] = 'o',
	[0x19] = 'p',

	[0x1A] = '[',
	[0x1B] = ']',
	[0x1C] = '\n',
	[0x2B] = '\\',

	[0x1E] = 'a',
	[0x1F] = 's',
	[0x20] = 'd',
	[0x21] = 'f',
	[0x22] = 'g',
	[0x23] = 'h',
	[0x24] = 'j',
	[0x25] = 'k',
	[0x26] = 'l',

	[0x27] = ';',
	[0x28] = '\'',

	[0x2C] = 'z',
	[0x2D] = 'x',
	[0x2E] = 'c',
	[0x2F] = 'v',
	[0x30] = 'b',
	[0x31] = 'n',
	[0x32] = 'm',
	[0x33] = ',',
	[0x34] = '.',
	[0x35] = '/',

	[0x39] = ' ',
};

static const char scancode_to_ascii_shifted[128] __attribute__((section(".text"))) = {
	[0x29] = '~',
	[0x02] = '!',
	[0x03] = '@',
	[0x04] = '#',
	[0x05] = '$',
	[0x06] = '%',
	[0x07] = '^',
	[0x08] = '&',
	[0x09] = '*',
	[0x0A] = '(',
	[0x0B] = ')',
	[0x0C] = '_',
	[0x0D] = '+',
	[0x0E] = '\b',

	[0x10] = 'Q',
	[0x11] = 'W',
	[0x12] = 'E',
	[0x13] = 'R',
	[0x14] = 'T',
	[0x15] = 'Y',
	[0x16] = 'U',
	[0x17] = 'I',
	[0x18] = 'O',
	[0x19] = 'P',

	[0x1A] = '{',
	[0x1B] = '}',
	[0x1C] = '\n',
	[0x2B] = '|',

	[0x1E] = 'A',
	[0x1F] = 'S',
	[0x20] = 'D',
	[0x21] = 'F',
	[0x22] = 'G',
	[0x23] = 'H',
	[0x24] = 'J',
	[0x25] = 'K',
	[0x26] = 'L',

	[0x27] = ':',
	[0x28] = '"',

	[0x2C] = 'Z',
	[0x2D] = 'X',
	[0x2E] = 'C',
	[0x2F] = 'V',
	[0x30] = 'B',
	[0x31] = 'N',
	[0x32] = 'M',
	[0x33] = '<',
	[0x34] = '>',
	[0x35] = '?',

	[0x39] = ' ',
};

static inline void outb(uint16_t port, uint8_t val) {
	asm volatile("outb %0, %1" : : "a"(val), "Nd"(port));
}

static inline uint8_t inb(uint16_t port) {
	uint8_t ret;
	asm volatile("inb %1, %0" : "=a"(ret) : "Nd"(port));
	return ret;
}

uint8_t keyboard_read_scan_code() {
	while (!(inb(KB_STATUS_PORT) & KB_OBF));
	return inb(KB_DATA_PORT);
}
void draw_char(int x, int y, int c, uint32_t color, uint32_t *framebuffer, uint32_t width)
{
	char *glyph = font8x8_basic[(unsigned char)c];

	for (int row = 0; row < 8; row++) {
		for (int col = 0; col < 8; col++) {
			if (glyph[row] & (1 << col)) {
				framebuffer[(y + row) * width + (x + col)] = color;
			}
		}
	}
}

void draw_string(int x, int y, const char *str, uint32_t color, uint32_t *framebuffer, uint32_t width)
{
	while (*str) {
		draw_char(x, y, *str, color, framebuffer, width);
		x += 8;
		str++;
	}
}

void term_init(uint32_t *framebuffer, uint32_t width, uint32_t height)
{
	g_framebuffer = framebuffer;
	g_width = width;
	g_height = height;
	term_col = 0;
	term_row = 0;
}

void term_set_color(uint32_t color)
{
	g_default_color = color;
}

void term_printf(const char *str)
{
	while (*str) {
		if (*str == '\n') {
			term_col = 0;
			term_row++;
			str++;
			continue;
		}

		if ((term_col * 8) >= g_width) {
			term_col = 0;
			term_row++;
		}

		if ((term_row * 8) >= g_height) {
			term_row = 0; // just simple wrap around for now, scroll later
		}

		draw_char(term_col * 8, term_row * 8, *str, g_default_color, g_framebuffer, g_width);

		term_col++;
		str++;
	}
}

void shell() {
	term_set_color(0xFCD24D);
	term_printf("\n> ");
	term_set_color(0xFFFFFF);
	while (1) {
		uint8_t scancode = keyboard_read_scan_code();
	
		// shift or no shift????
		if (scancode == 0x2A) kbd_shifted = true;
		if (scancode == 0xAA) kbd_shifted = false;

		// we dont care abt key releases
		if (scancode & 0x80) continue;

		char c = kbd_shifted ? scancode_to_ascii_shifted[scancode] : scancode_to_ascii[scancode];

		if (c) {
			if (c == '\n') {
				// enter, interpret command
				// we dont know what to do with command yet so new prompt and pretend we did something
				// we also need to add like handling of the current command, do that soon!
				term_set_color(0xFCD24D);
				term_printf("\n> ");
				term_set_color(0xFFFFFF);
			}
			if (c == '\b') {
				// stupid nut keep trying to use backspace when its not done yet, just add a handler placeholder
				term_printf("\n---\nyou stupid nut!\n");
				term_printf("we dont have backspace yet, stop trying to when testing! get better\n");
				term_set_color(0xFCD24D);
				term_printf("\n> ");
				term_set_color(0xFFFFFF);
			}
			else {
				term_printf(&c);
			}
		}
	}
}

void kernel_main(struct multiboot_info *mbi) 
{
	// check if framebuffer info is available (bit 12)
	if (!(mbi->flags & (1 << 12))) {
		while(1) __asm__("hlt");
	}

	// get the framebuffer
	uint32_t *framebuffer = (uint32_t*)(uintptr_t)mbi->framebuffer_addr;
	uint32_t width = mbi->framebuffer_width;
	uint32_t height = mbi->framebuffer_height;

	// draw text to the framebuffer
	term_init(framebuffer, width, height);
	term_printf("welcome to ");
	term_set_color(0xFCD24D);
	term_printf("FrenchToastOS!\n");
	term_set_color(0xFFFFFF);
	term_printf("developed by ");
	term_set_color(0x967BB6);
	term_printf("Arslaan Pathan\n");
	term_set_color(0xFFFFFF);
	term_printf("---\n");
	term_printf("https://arslaancodes.com\n");

	term_printf("\n---\nShell:\n");
	shell();

	// if theres nothing left to do, halt the cpu or else cooked
	// our boot.s already does this but better to be safe than sorry
	while (1) {
		__asm__ __volatile__ ("hlt");
	}
}