Shard/ShardOS/kernel.c

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

// 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;
}

static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;
static uint16_t* const VGA_MEMORY = (uint16_t*) 0xB8000;

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_LIGHT_GREY, VGA_COLOR_BLACK);
    terminal_buffer = VGA_MEMORY;
    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_writestring(const char* data) {
    size_t datalen = strlen(data);
    for (size_t i = 0; i < datalen; i++) {
        terminal_buffer[terminal_row * VGA_WIDTH + terminal_column] = vga_entry(data[i], terminal_color);
        if (++terminal_column == VGA_WIDTH) {
            terminal_column = 0;
            if (++terminal_row == VGA_HEIGHT) {
                terminal_row = 0;
            }
        }
    }
}

void kernel_main(void) {
    terminal_initialize();
    terminal_writestring("Kernel main running...\n");
    terminal_writestring("ShardOS, Developed by apfelteesaft\n");
    while (1);
}