kernel/16bit/init16bit.asm

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                     Christoffer Bubach, 2005. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;     Do everything related to 16-bit here... :)           ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8
   9 ;---------------------;
  10 ;    save info        ;
  11 ;---------------------;
  12 init16bit:
  13         call   getmem                                 ; realmode/mem.inc
  14         mov    [ram_amount], eax
  15
  16         xor    eax, eax                               ; clear mem for IDT and GDT
  17         mov    edi, [idtr.address]                    ; IDT address
  18         mov    ecx, (0x800 + 0x800)/4
  19         rep    stosd
  20
  21         mov    eax, cs
  22         shl    eax, 4
  23         mov    [gdt.BOS_16code + 2], ax               ; Prepare GDT by
  24         mov    [gdt.BOS_16data + 2], ax               ; setting 16-bit base.
  25         shr    eax, 16
  26         mov    [gdt.BOS_16code + 4], al
  27         mov    [gdt.BOS_16data + 4], al
  28         mov    [gdt.BOS_16code + 7], ah
  29         mov    [gdt.BOS_16data + 7], ah
  30
  31         lea    esi, [gdt]
  32         mov    edi, 0x7400                            ; GDT address
  33         mov    ecx, (gdt_end - gdt)/4
  34         rep    movsd                                  ; Move it to final pos.
  35
  36         push   dword 0                                ; clear NT bit
  37         popfd
  38         ret