PUBLIC _enableUnchainedVGAMode
PUBLIC _enableTextMode

DISPLAY_MODE_VGA equ 13h
DISPLAY_MODE_TEXT equ 03h

VGA_SEQUENCE_CONTROLLER_INDEX equ 0x3c4
VGA_SEQUENCE_CONTROLLER_DATA equ 0x3c5h
VGA_SEQUENCE_CONTROLLER_MEMORY_MODE equ 0x04

VGA_CRT_CONTROLLER_INDEX equ 0x03d4
VGA_CRT_CONTROLLER_DATA equ 0x03d5
VGA_CRT_CONTROLLER_UNDERLINE_LOC equ 0x14
VGA_CRT_CONTROLLER_MODE_CONTROL equ 0x17

.386
.model flat,c

.CODE

_enableUnchainedVGAMode:
  mov ax,0x0013;
  int 0x10

  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
  mov al, VGA_SEQUENCE_CONTROLLER_MEMORY_MODE
  mov ah, 0x06
  out dx, ax

  mov dx, VGA_CRT_CONTROLLER_INDEX
  mov al, VGA_CRT_CONTROLLER_MODE_CONTROL
  mov ah, 0xe3
  out dx, ax

  mov dx, VGA_CRT_CONTROLLER_INDEX
  mov al, VGA_CRT_CONTROLLER_UNDERLINE_LOC
  mov ah, 0x00
  out dx, ax

  ret

_enableTextMode:
  mov ah,0h
  mov al,DISPLAY_MODE_TEXT
  int 10h
  ret

end