Category : Printer + Display Graphics
Archive   : DISP160.ZIP
Filename : AHEADA.ASM

; This is file AHEADA.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 0 ; 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 640
def_gh dw 480

;--------------------------------------------------------------------------
; 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
dw 60h, 640, 400
dw 61h, 640, 480
dw 62h, 800, 600
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,62h
int 10h
mov cx,800
mov dx,600
ret

init_8: ; biggest graphics
mov ax,62h
int 10h
mov cx,800
mov dx,600
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
;
; Derived from VGAKIT Version 3.4
; Copyright 1988,89,90 John Bridges

assume ds:nothing, es:nothing

paging_routine proc far
mov ch,al
mov dx,3ceh ;Enable extended registers
mov ax,200fh
out dx,ax
mov dl,0cch ;bit 0
in al,dx
mov dl,0c2h
and al,11011111b
shr ch,1
jnc skpa
or al,00100000b
skpa: out dx,al
mov dl,0cfh ;bits 1,2,3
mov al,0
out dx,al
inc dx
in al,dx
dec dx
and al,11111000b
or al,ch
mov ah,al
mov al,0
out dx,ax

ret
paging_routine endp

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

cseg ends
end