main.c

#include "ioport.h"
#include "gdt.h"
#include "idt.h"

void clear_screen();      /* clear screen */
void putc(char aChar);    /* print a single char on screen */
void puts(char *aString); /* print a string on the screen */
void puthex(int aNumber); /* print an Hex number on screen */

void empty_irq(int_regs_t *r)
{
}

/* multiboot entry-point with datastructure as arg. */
void main(unsigned int *mboot_info)
{
  /* clear the screen */
  clear_screen();
  puts("Early boot.\n");
  puts("\t-> Setting up the GDT... ");
  gdt_init_default();
  puts("done\n");

  puts("\t-> Setting up the IDT... ");
  setup_idt();
  puts("OK\n");

  puts("\n\n");

  idt_setup_handler(0, empty_irq);
  idt_setup_handler(0, empty_irq);

  __asm volatile("sti");

  /* minimal setup done ! */

  puts("Hello world\n\n");

  for (;;)
    ; /* nothing more to do... really nothing ! */
}

/* base address for the video output assume to be set as character oriented by the multiboot */
unsigned char *video_memory = (unsigned char *)0xB8000;

/* clear screen */
void clear_screen()
{
  int i;
  for (i = 0; i < 80 * 25; i++)
  {                                           /* for each one of the 80 char by 25 lines */
    video_memory[i * 2 + 1] = 0x0F;           /* color is set to black background and white char */
    video_memory[i * 2] = (unsigned char)' '; /* character shown is the space char */
  }
}

/* print a string on the screen */
void puts(char *aString)
{
  char *current_char = aString;
  while (*current_char != 0)
  {
    putc(*current_char++);
  }
}

/* print an number in hexa */
char *hex_digit = "0123456789ABCDEF";
void puthex(int aNumber)
{
  int i;
  int started = 0;
  for (i = 28; i >= 0; i -= 4)
  {
    int k = (aNumber >> i) & 0xF;
    if (k != 0 || started)
    {
      putc(hex_digit[k]);
      started = 1;
    }
  }
}

/* print a char on the screen */
int cursor_x = 0; /* here is the cursor position on X [0..79] */
int cursor_y = 0; /* here is the cursor position on Y [0..24] */

void setCursor()
{
  int cursor_offset = cursor_x + cursor_y * 80;
  _outb(0x3d4, 14);
  _outb(0x3d5, ((cursor_offset >> 8) & 0xFF));
  _outb(0x3d4, 15);
  _outb(0x3d5, (cursor_offset & 0xFF));
}

void putc(char c)
{
  if (cursor_x > 79)
  {
    cursor_x = 0;
    cursor_y++;
  }
  if (cursor_y > 24)
  {
    cursor_y = 0;
    clear_screen();
  }
  switch (c)
  { /* deal with a special char */
  case '\r':
    cursor_x = 0;
    break; /* carriage return */
  case '\n':
    cursor_x = 0;
    cursor_y++;
    break; /* new ligne */
  case 0x8:
    if (cursor_x > 0)
      cursor_x--;
    break; /* backspace */
  case 0x9:
    cursor_x = (cursor_x + 8) & ~7;
    break; /* tabulation */
    /* or print a simple character */
  default:
    video_memory[(cursor_x + 80 * cursor_y) * 2] = c;
    cursor_x++;
    break;
  }
  setCursor();
}