/*  kernel.c - the C part of the kernel */
/*  Copyright (C) 1999, 2010  Free Software Foundation, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "multiboot2.h"

/*  Macros. */

/*  Some screen stuff. */
/*  The number of columns. */
#define COLUMNS                 80
/*  The number of lines. */
#define LINES                   24
/*  The attribute of an character. */
#define ATTRIBUTE               7
/*  The video memory address. */
#define VIDEO                   0xB8000

/*  Variables. */
/*  Save the X position. */
static int xpos;
/*  Save the Y position. */
static int ypos;
/*  Point to the video memory. */
static volatile unsigned char *video;

/*  Forward declarations. */
void cmain (unsigned long magic, unsigned long addr);
static void cls (void);
static void itoa (char *buf, int base, int d);
static void putchar (int c);
void printf (const char *format, ...);

/*  Check if MAGIC is valid and print the Multiboot information structure
   pointed by ADDR. */
void
cmain (unsigned long magic, unsigned long addr)
{  
  struct multiboot_tag *tag;
  unsigned size;

  /*  Clear the screen. */
  cls ();

  /*  Am I booted by a Multiboot-compliant boot loader? */
  if (magic != MULTIBOOT2_BOOTLOADER_MAGIC)
    {
      printf ("Invalid magic number: 0x%x\n", (unsigned) magic);
      return;
    }

  if (addr & 7)
    {
      printf ("Unaligned mbi: 0x%x\n", addr);
      return;
    }

  size = *(unsigned *) addr;
  printf ("Announced mbi size 0x%x\n", size);
  for (tag = (struct multiboot_tag *) (addr + 8);
       tag->type != MULTIBOOT_TAG_TYPE_END;
       tag = (struct multiboot_tag *) ((multiboot_uint8_t *) tag 
                                       + ((tag->size + 7) & ~7)))
    {
      printf ("Tag 0x%x, Size 0x%x\n", tag->type, tag->size);
      switch (tag->type)
        {
        case MULTIBOOT_TAG_TYPE_CMDLINE:
          printf ("Command line = %s\n",
                  ((struct multiboot_tag_string *) tag)->string);
          break;
        case MULTIBOOT_TAG_TYPE_BOOT_LOADER_NAME:
          printf ("Boot loader name = %s\n",
                  ((struct multiboot_tag_string *) tag)->string);
          break;
        case MULTIBOOT_TAG_TYPE_MODULE:
          printf ("Module at 0x%x-0x%x. Command line %s\n",
                  ((struct multiboot_tag_module *) tag)->mod_start,
                  ((struct multiboot_tag_module *) tag)->mod_end,
                  ((struct multiboot_tag_module *) tag)->cmdline);
          break;
        case MULTIBOOT_TAG_TYPE_BASIC_MEMINFO:
          printf ("mem_lower = %uKB, mem_upper = %uKB\n",
                  ((struct multiboot_tag_basic_meminfo *) tag)->mem_lower,
                  ((struct multiboot_tag_basic_meminfo *) tag)->mem_upper);
          break;
        case MULTIBOOT_TAG_TYPE_BOOTDEV:
          printf ("Boot device 0x%x,%u,%u\n",
                  ((struct multiboot_tag_bootdev *) tag)->biosdev,
                  ((struct multiboot_tag_bootdev *) tag)->slice,
                  ((struct multiboot_tag_bootdev *) tag)->part);
          break;
        case MULTIBOOT_TAG_TYPE_MMAP:
          {
            multiboot_memory_map_t *mmap;

            printf ("mmap\n");
      
            for (mmap = ((struct multiboot_tag_mmap *) tag)->entries;
                 (multiboot_uint8_t *) mmap 
                   < (multiboot_uint8_t *) tag + tag->size;
                 mmap = (multiboot_memory_map_t *) 
                   ((unsigned long) mmap
                    + ((struct multiboot_tag_mmap *) tag)->entry_size))
              printf (" base_addr = 0x%x%x,"
                      " length = 0x%x%x, type = 0x%x\n",
                      (unsigned) (mmap->addr >> 32),
                      (unsigned) (mmap->addr & 0xffffffff),
                      (unsigned) (mmap->len >> 32),
                      (unsigned) (mmap->len & 0xffffffff),
                      (unsigned) mmap->type);
          }
          break;
        case MULTIBOOT_TAG_TYPE_FRAMEBUFFER:
          {
            multiboot_uint32_t color;
            unsigned i;
            struct multiboot_tag_framebuffer *tagfb
              = (struct multiboot_tag_framebuffer *) tag;
            void *fb = (void *) (unsigned long) tagfb->common.framebuffer_addr;

            switch (tagfb->common.framebuffer_type)
              {
              case MULTIBOOT_FRAMEBUFFER_TYPE_INDEXED:
                {
                  unsigned best_distance, distance;
                  struct multiboot_color *palette;
            
                  palette = tagfb->framebuffer_palette;

                  color = 0;
                  best_distance = 4*256*256;
            
                  for (i = 0; i < tagfb->framebuffer_palette_num_colors; i++)
                    {
                      distance = (0xff - palette[i].blue) 
                        * (0xff - palette[i].blue)
                        + palette[i].red * palette[i].red
                        + palette[i].green * palette[i].green;
                      if (distance < best_distance)
                        {
                          color = i;
                          best_distance = distance;
                        }
                    }
                }
                break;

              case MULTIBOOT_FRAMEBUFFER_TYPE_RGB:
                color = ((1 << tagfb->framebuffer_blue_mask_size) - 1) 
                  << tagfb->framebuffer_blue_field_position;
                break;

              case MULTIBOOT_FRAMEBUFFER_TYPE_EGA_TEXT:
                color = '\\' | 0x0100;
                break;

              default:
                color = 0xffffffff;
                break;
              }
            
            for (i = 0; i < tagfb->common.framebuffer_width
                   && i < tagfb->common.framebuffer_height; i++)
              {
                switch (tagfb->common.framebuffer_bpp)
                  {
                  case 8:
                    {
                      multiboot_uint8_t *pixel = fb
                        + tagfb->common.framebuffer_pitch * i + i;
                      *pixel = color;
                    }
                    break;
                  case 15:
                  case 16:
                    {
                      multiboot_uint16_t *pixel
                        = fb + tagfb->common.framebuffer_pitch * i + 2 * i;
                      *pixel = color;
                    }
                    break;
                  case 24:
                    {
                      multiboot_uint32_t *pixel
                        = fb + tagfb->common.framebuffer_pitch * i + 3 * i;
                      *pixel = (color & 0xffffff) | (*pixel & 0xff000000);
                    }
                    break;

                  case 32:
                    {
                      multiboot_uint32_t *pixel
                        = fb + tagfb->common.framebuffer_pitch * i + 4 * i;
                      *pixel = color;
                    }
                    break;
                  }
              }
            break;
          }

        }
    }
  tag = (struct multiboot_tag *) ((multiboot_uint8_t *) tag 
                                  + ((tag->size + 7) & ~7));
  printf ("Total mbi size 0x%x\n", (unsigned) tag - addr);
}    

/*  Clear the screen and initialize VIDEO, XPOS and YPOS. */
static void
cls (void)
{
  int i;

  video = (unsigned char *) VIDEO;
  
  for (i = 0; i < COLUMNS * LINES * 2; i++)
    *(video + i) = 0;

  xpos = 0;
  ypos = 0;
}

/*  Convert the integer D to a string and save the string in BUF. If
   BASE is equal to ’d’, interpret that D is decimal, and if BASE is
   equal to ’x’, interpret that D is hexadecimal. */
static void
itoa (char *buf, int base, int d)
{
  char *p = buf;
  char *p1, *p2;
  unsigned long ud = d;
  int divisor = 10;
  
  /*  If %d is specified and D is minus, put ‘-’ in the head. */
  if (base == 'd' && d < 0)
    {
      *p++ = '-';
      buf++;
      ud = -d;
    }
  else if (base == 'x')
    divisor = 16;

  /*  Divide UD by DIVISOR until UD == 0. */
  do
    {
      int remainder = ud % divisor;
      
      *p++ = (remainder < 10) ? remainder + '0' : remainder + 'a' - 10;
    }
  while (ud /= divisor);

  /*  Terminate BUF. */
  *p = 0;
  
  /*  Reverse BUF. */
  p1 = buf;
  p2 = p - 1;
  while (p1 < p2)
    {
      char tmp = *p1;
      *p1 = *p2;
      *p2 = tmp;
      p1++;
      p2--;
    }
}

/*  Put the character C on the screen. */
static void
putchar (int c)
{
  if (c == '\n' || c == '\r')
    {
    newline:
      xpos = 0;
      ypos++;
      if (ypos >= LINES)
        ypos = 0;
      return;
    }

  *(video + (xpos + ypos * COLUMNS) * 2) = c & 0xFF;
  *(video + (xpos + ypos * COLUMNS) * 2 + 1) = ATTRIBUTE;

  xpos++;
  if (xpos >= COLUMNS)
    goto newline;
}

/*  Format a string and print it on the screen, just like the libc
   function printf. */
void
printf (const char *format, ...)
{
  char **arg = (char **) &format;
  int c;
  char buf[20];

  arg++;
  
  while ((c = *format++) != 0)
    {
      if (c != '%')
        putchar (c);
      else
        {
          char *p, *p2;
          int pad0 = 0, pad = 0;
          
          c = *format++;
          if (c == '0')
            {
              pad0 = 1;
              c = *format++;
            }

          if (c >= '0' && c <= '9')
            {
              pad = c - '0';
              c = *format++;
            }

          switch (c)
            {
            case 'd':
            case 'u':
            case 'x':
              itoa (buf, c, *((int *) arg++));
              p = buf;
              goto string;
              break;

            case 's':
              p = *arg++;
              if (! p)
                p = "(null)";

            string:
              for (p2 = p; *p2; p2++);
              for (; p2 < p + pad; p2++)
                putchar (pad0 ? '0' : ' ');
              while (*p)
                putchar (*p++);
              break;

            default:
              putchar (*((int *) arg++));
              break;
            }
        }
    }
}