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kernel.c
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kernel.c
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#include <stddef.h>
#include <stdint.h>
/* Check if the compiler thinks we are targeting the wrong operating system*/
#if defined(__linux__)
#error "You are not using a cross-compiler, you will most certainly run into trouble"
#endif
/* This only works with 32-bit ix86 targets. */
#if !defined(__i386__)
#error "This must 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,
};
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 = 24;
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 = (uint16_t*)0xB8000;
for(size_t i = 0; i < VGA_HEIGHT; i++) {
for(size_t j = 0; j < VGA_WIDTH; j++) {
const size_t index = i * VGA_WIDTH + j;
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 i, size_t j) {
const size_t index = i * VGA_WIDTH + j;
terminal_buffer[index] = vga_entry(c, color);
}
void terminal_putchar(char c) {
if(c == '\n') {
++terminal_row;
terminal_column = 0;
return;
}
terminal_putentryat(c, terminal_color, terminal_row, terminal_column);
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) {
terminal_initialize();
terminal_writestring("hello, kernal world!\n");
}