使用VESA示例

;;
;; vesaModes.s (adapted from Visopsys OS-loader)
;;
;; Copyright (c) 2000, J. Andrew McLaughlin
;; You're free to use this code in any manner you like, as long as this
;; notice is included (and you give credit where it is due), and as long
;; as you understand and accept that it comes with NO WARRANTY OF ANY KIND.
;; Contact me at <andy@visopsys.org> about any bugs or problems.
;;

;; Change this to zero if you don't require Linear Framebuffer
;; abilities in your graphics modes.  This could be turned into
;; a function parameter of the routine below, if desired.
%define REQUIRELFB 1

BITS 16

findGraphicMode:
;; The VESA 2.0 specification states that they will no longer
;; create standard video mode numbers, and video card vendors are
;; no longer required to support the old numbers.  This routine
;; will dynamically find a supported mode number from the VIDEO BIOS,
;; according to the desired resolutions, etc.

;; The function takes parameters that describe the desired graphic
;; mode, (X resolution, Y resolution, and Bits Per Pixel) and returns
; the VESA mode number in EAX, if found.  Returns 0 on error.

;; The C prototype for this function would look like the following:
;; int findGraphicMode(short int x_res, short int y_res,
;;                     short int bpp);
;; (Push bpp, then y_res, then x_res onto the 16-bit stack before
;; calling.  Caller pops them off again after the call.)

;; Save space on the stack for the mode number we're returning
sub SP, 2

;; Save regs
pusha

;; Save the stack pointer
mov BP, SP

;; By default, return the value 0 (failure)
mov word [SS:(BP + 16)], 0

;; Get the VESA info block.  Save ES, since this call could
;; destroy it
push ES
mov DI, VESAINFO
mov AX, 4F00h
int 10h
;; Restore ES
pop ES

cmp AX, 004Fh
;; Fail
jne .done

;; We need to get a far pointer to a list of graphics mode numbers
;; from the VESA info block we just retrieved.  Get the offset now,
;; and the segment inside the loop.
mov SI, [VESAINFO + 0Eh]

;; Do a loop through the supported modes
.modeLoop:

;; Save ES
push ES

;; Now get the segment of the far pointer, as mentioned above
mov AX, [VESAINFO + 10h]
mov ES, AX

;; ES:SI is now a pointer to the next supported mode.  The list
;; terminates with the value FFFFh

;; Get the first/next mode number
mov DX, word [ES:SI]

;; Restore ES
pop ES

;; Is it the end of the mode number list?
cmp DX, 0FFFFh
je near .done

;; Increment the pointer for the next loop
add SI, 2

;; We have a mode number.  Now we need to do a VBE call to
;; determine whether this mode number suits our needs.
;; This call will put a bunch of info in the buffer pointed to
;; by ES:DI

mov CX, DX
mov AX, 4F01h
mov DI, MODEINFO
int 10h

;; Make sure the function call is supported
cmp AL, 4Fh
;; Fail
jne near .done

;; Is the mode supported by this call? (sometimes, they're not)
cmp AH, 00h
jne .modeLoop

;; We need to look for a few features to determine whether this
;; is the mode we want.  First, it needs to be supported, and it
;; needs to be a graphics mode.  Next, it needs to match the
;; requested attributes of resolution and BPP

;; Get the first word of the buffer
mov AX, word [MODEINFO]

;; Is the mode supported?
bt AX, 0
jnc .modeLoop

;; Is this mode a graphics mode?
bt AX, 4
jnc .modeLoop

%if REQUIRELFB
;; Does this mode support a linear frame buffer?
bt AX, 7
jnc .modeLoop
%endif

;; Does the horizontal resolution of this mode match the requested
;; number?
mov AX, word [MODEINFO + 12h]
cmp AX, word [SS:(BP + 20)]
jne near .modeLoop

;; Does the vertical resolution of this mode match the requested
;; number?
mov AX, word [MODEINFO + 14h]
cmp AX, word [SS:(BP + 22)]
jne near .modeLoop

;; Do the Bits Per Pixel of this mode match the requested number?
xor AX, AX
mov AL, byte [MODEINFO + 19h]
cmp AX, word [SS:(BP + 24)]
jne near .modeLoop

;; If we fall through to here, this is the mode we want.
mov word [SS:(BP + 16)], DX

.done:
popa
;; Return the mode number
xor EAX, EAX
pop AX
ret

;;
;; The data segment
;;

SEGMENT .data
ALIGN 4

VESAINFO  	db 'VBE2'		;; Space for info ret by vid BIOS
times 508  db 0
MODEINFO	times 256 db 0