kernel/realmode/mem.inc

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                Christoffer Bubach, 2003-2005. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;      Get memory size, only using E801 right now.         ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8
   9 ;-----------------------------------------;
  10 ;  get mem                                ;
  11 ;   in:  nothing                          ;
  12 ;   out: eax = mem in bytes, 0 = error    ;
  13 ;-----------------------------------------;
  14 getmem:
  15           push    dx
  16           push    cx
  17           push    ebx
  18
  19           xor     eax, eax
  20           xor     ebx, ebx
  21           mov     ax, 0xE801
  22           xor     dx, dx
  23           xor     cx, cx
  24           int     0x15
  25           jnc     .cont1
  26           xor     eax, eax
  27           jmp     .end                                ; failed! :'(
  28
  29      .cont1:
  30           mov     si, ax
  31           or      si, bx
  32           jne     .cont
  33           mov     ax, cx
  34           mov     bx, dx
  35
  36      .cont:
  37           cmp     ax, 0x3C00
  38           jb      .below_16
  39           movzx   eax, bx
  40           add     eax, 0x100
  41           shl     eax, 16                             ; eax = eax * 65536
  42           jmp     .end
  43
  44      .below_16:
  45           shl     eax, 10                             ; eax = eax * 1024
  46
  47      .end:
  48           pop     ebx
  49           pop     cx
  50           pop     dx
  51           ret