kernel/init/bios.asm

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                Christoffer Bubach, 2003-2005. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;        Goes back to realmode to do an INT.               ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8
   9
  10 rmode_int:
  11           pushad
  12           push    eax
  13           shr     eax, 16                             ; move high bits to ax
  14           mov     word [realmode_ax], ax              ; save new ax value
  15           pop     eax                                 ; restore
  16
  17           push    ebx
  18           shr     ebx, 16                             ; move high bits to bx
  19           mov     byte [int_number], bl               ; save int number to call
  20           pop     ebx
  21
  22           mov     byte [realmode_error], 0            ; all variables is in the
  23           mov     word [realmode_bx], bx              ; realmode/variables.inc file
  24           mov     word [realmode_cx], cx
  25           mov     word [realmode_dx], dx
  26           call    disable_irqs
  27           jmp     pword 0x18:do_16pmode       ; must substract 0x10000 from
  28                                                       ; data addresses becasue of
  29                                                       ; fasm strict "org" behavior
  30 use16
  31 do_16pmode:
  32           mov     ax, 0x20
  33           mov     ds, ax
  34           mov     es, ax
  35           mov     fs, ax
  36           mov     gs, ax
  37           mov     ss, ax
  38
  39           cli
  40           mov     eax, cr0
  41           and     al, 0xFE
  42           mov     cr0, eax
  43
  44           jmp     0x1000:(do_realm)
  45
  46 do_realm:
  47           mov     ax, cs
  48           mov     ds, ax
  49
  50           xor     ax, ax
  51           mov     es, ax
  52           mov     fs, ax
  53           mov     gs, ax
  54           mov     ss, ax
  55
  56           lidt    [ridtr]                     ; realmode/variables.inc
  57           sti
  58
  59           mov     ax, word [realmode_ax]
  60           mov     bx, word [realmode_bx]
  61           mov     cx, word [realmode_cx]
  62           mov     dx, word [realmode_dx]
  63
  64           push    ax                                  ; this is some cool shit.. ;)
  65           mov     al, [int_number]            ; interrupt to preform
  66           mov     [$+5], al                   ; move it to right pos.
  67           pop     ax
  68           db      0xCD                                ; opcode for int.
  69           db      0x00                                ; move int_number here
  70
  71           jnc     .no_error
  72           mov     byte [realmode_error], 1
  73
  74      .no_error:
  75           mov     word [realmode_ax], ax
  76           mov     word [realmode_bx], bx
  77           mov     word [realmode_cx], cx
  78           mov     word [realmode_dx], dx
  79
  80           cli
  81
  82           lgdt    [gdtr]
  83           lidt    [idtr]
  84           mov     eax, cr0
  85           or      al, 1
  86           mov     cr0, eax
  87
  88           jmp     pword 0x08:gobackto_pm
  89
  90
  91 use32
  92 gobackto_pm:
  93           mov     ax, 0x10                            ; refresh all segment registers
  94           mov     ds, ax
  95           mov     es, ax
  96           mov     fs, ax
  97           mov     gs, ax
  98           mov     ss, ax
  99           call    enable_irqs
 100           sti
 101           popad
 102           clc                                         ; clear carry.
 103           cmp     [realmode_error], 1                 ; if error, then
 104           jne     .end
 105           stc                                         ; set carry.
 106      .end:
 107           ret