I can boot it in real hardware, which is pretty good. But it reboots the PC. My BIOS menu is written in C, and rebooting from there normally gives a few frames of VESA/VGA garbage, then reboots properly. The same happens on the fulldisk.img i have created, suggesting the C code is rebooting for some reason. The assembly bootloader loads Protected mode and loads the GDTR, and then at the very end switches to 32 bit right before the jump to 0x07E00 instruction, which should make it protected mode 32 bit and NASM compiled it correctly. I do 0x13 before moving to 32bit protected mode, THEN jump to protected mode and go to 32bit code, then jump to the myos.bin/boot.asm. The A20 line is not enabled.
Here is the code:
Code: Select all
/* Surely you will remove the processor conditionals and this comment
appropriately depending on whether or not you use C++. */
#if !defined(__cplusplus)
#include <stdbool.h> /* C doesn't have booleans by default. */
#endif
#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 tutorial will only work for the 32-bit ix86 targets. */
#if !defined(__i386__)
#error "This tutorial 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,
};
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_LIGHT_GREY, 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) {
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));
}
#if defined(__cplusplus)
extern "C" /* Use C linkage for kernel_main. */
#endif
void kernel_main(void) {
/* Initialize terminal interface */
terminal_initialize();
/* Newline support is left as an exercise. */
terminal_writestring("C");
}Why is my hardware rebooting?
If you're even asking for the motherboard:
H81 model, GIGABYTE vendor, UEFI.
I don't have an option to boot from UEFI on the USB.
