; This is file VGA.ASM
;
; Copyright (C) 1991 DJ Delorie, 24 Kirsten Ave, Rochester NH 03867-2954
;
; This file is distributed under the terms listed in the document
; "copying.dj", available from DJ Delorie at the address above.
; A copy of "copying.dj" should accompany this file; if not, a copy
; should be available from where this file was obtained.  This file
; may not be distributed without a verbatim copy of "copying.dj".
;
; This file is distributed WITHOUT ANY WARRANTY; without even the implied
; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
;

cseg	segment	byte public 'code'
	assume	cs:cseg, ds:cseg, es:cseg, ss:nothing

	dw	offset init_routine
	dw	offset paging_routine
	dw	1	; set to 1 if separate read & write windows or
			; only 64K of video RAM (ie: no paging)

def_tw	dw	80	; filled in by go32 if GO32 env. var. is set
def_th	dw	25
def_gw	dw	320
def_gh	dw	200

;--------------------------------------------------------------------------
; Entry: AX=mode selection
;		0=80x25 text
;		1=default text
;		2=text CX cols by DX rows
;		3=biggest text
;		4=320x200 graphics
;		5=default graphics
;		6=graphics CX width by DX height
;		7=biggest non-interlaced graphics
;		8=biggest graphics
;
; NOTE: This runs in real mode, but don't mess with the segment registers.
;
; Exit:  CX=width (in pixels or characters)
;        DX=height

init_table	label	word
	dw	offset init_0
	dw	offset init_1
	dw	offset init_2
	dw	offset init_3
	dw	offset init_4
	dw	offset init_5
	dw	offset init_6
	dw	offset init_7
	dw	offset init_8

init_routine	proc	far
	cmp	ax,8
	jbe	valid_req
	ret
valid_req:
	shl	ax,1
	mov	bx,ax
	jmp	init_table[bx]

init_0: ; 80x25 text
	mov	ax,3
	int	10h
	mov	cx,80
	mov	dx,25
	ret

init_1: ; default text
	mov	cx,def_tw
	mov	dx,def_th
	jmp	init_2

init_2_table	label	word
	dw	01h, 40, 25
	dw	03h, 80, 25
init_2_tend	label	word

init_2: ; CX*DX text
	mov	si,offset init_2_table
init_2a:
	cmp	[si+2],cx
	jb	init_2b
	cmp	[si+4],dx
	jb	init_2b
	; got a big enough one!
	jmp	init_2c
init_2b:
	cmp	si,offset init_2_tend - 6
	je	init_2c
	add	si,6
	jmp	init_2a
init_2c:
	mov	ax,[si]
	push	si
	int	10h
	pop	si
	mov	cx,[si+2]
	mov	dx,[si+4]
	ret

init_3: ; biggest text
	mov	ax,[init_2_tend-6]
	int	10h
	mov	cx,[init_2_tend-4]
	mov	dx,[init_2_tend-2]
	ret

init_4: ; 320x200 graphics
	mov	ax,13h
	int	10h
	mov	cx,320
	mov	dx,200
	ret

init_5: ; default graphics - should be 640x480 if supported
	mov	cx,def_gw
	mov	dx,def_gh
	jmp	init_6

init_6_table	label	word
	dw	13h, 320, 200
init_6_tend	label	word

init_6: ; CX*DX graphics
	mov	si,offset init_6_table
init_6a:
	cmp	[si+2],cx
	jb	init_6b
	cmp	[si+4],dx
	jb	init_6b
	; got a big enough one!
	jmp	init_6c
init_6b:
	cmp	si,offset init_6_tend - 6
	je	init_6c
	add	si,6
	jmp	init_6a
init_6c:
	mov	ax,[si]
	push	si
	int	10h
	pop	si
	mov	cx,[si+2]
	mov	dx,[si+4]
	ret

init_7: ; biggest non-interlaced graphics
	mov	ax,13h
	int	10h
	mov	cx,320
	mov	dx,200
	ret

init_8: ; biggest graphics
	mov	ax,13h
	int	10h
	mov	cx,320
	mov	dx,200
	ret

init_routine	endp

;--------------------------------------------------------------------------
; Entry: AH=read page
;        AL=write page
;
; NOTE: This runs in protected mode!  Don't mess with the segment registers!
; This code must be relocatable and may not reference any data!
;
; Exit: VGA configured.
;       AX,BX,CX,DX,SI,DI may be trashed

	assume	ds:nothing, es:nothing

paging_routine	proc	far

	ret
paging_routine	endp

;--------------------------------------------------------------------------

cseg	ends
	end