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/* 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>
/* 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
/* 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,
};
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;
}
#define VGA_WIDTH 80
#define VGA_HEIGHT 25
#define VGA_MEMORY 0xB8000
size_t terminal_row;
size_t terminal_column;
uint8_t terminal_color;
uint16_t* terminal_buffer = (uint16_t*)VGA_MEMORY;
void terminal_initialize(void)
{
terminal_row = 0;
terminal_column = 0;
terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
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;
return;
}
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));
}
void kernel_main(void)
{
/* Initialize terminal interface */
terminal_initialize();
terminal_writestring("loading FrenchToastOS...\n");
terminal_writestring("developed by Arslaan Pathan");
/* if there is nothing else to do, halt, or the computer commit die */
/* our boot.s code does this already, but better to be safe than f**ked */
while (1) {
__asm__ __volatile__ ("hlt");
}
}
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