kernel/realmode/do_all_16bit.inc

   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 do_all_16bit:
  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, 0x6c00                         ; 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