Category : Assembly Language Source Code
Archive   : VGAKIT60.ZIP
Filename : BANKS.ASM

include model.inc
include vesa.inc
;
; VGAKIT Version 6.0
;
; Copyright 1988,89,90,91,92,93,94 John Bridges
; Free for use in commercial, shareware or freeware applications
;
; BANKS.ASM
;
.data?

public curbk

curbk dw ?

public vgamem,bksize

vgamem dw ? ;amount of memory on VGA card in K
bksize dw ? ;size of memory banks in K

extern justvesa:word ;only check for VESA, no chipset tests
extern novesa:word ;disable all VESA VBE checks
extern nosvga:word ;disable all SVGA checks including VESA

public cirrus,everex,acumos,paradise,tseng,trident,t8900
public ativga,aheada,aheadb,oaktech,video7
public chipstech,tseng4,genoa,ncr,compaq,vesa,dactype

cirrus dw ?
everex dw ?
acumos dw ?
paradise dw ?
tseng dw ?
trident dw ?
t8900 dw ?
ativga dw ?
aheada dw ?
aheadb dw ?
oaktech dw ? ;Oak Technology Inc OTI-067 and OTI-077
video7 dw ?
chipstech dw ?
tseng4 dw ?
genoa dw ?
ncr dw ?
compaq dw ?
vesa dw ?

dactype dw ? ; 0 = Normal DAC
; 1 = Sierra SC11481, SC11486, SC11488
; 2 = Sierra SC11485, SC11487, SC11489
; 3 = AT&T ATT20C491
; 4 = ACUMOS ADAC1

first dw ? ;flag so whichvga() is only called once
retval dw ? ;first return value from whichvga()

.data

OSEG equ SS: ;segment override for variable access

public bankadr

if @Codesize
bankadr dw offset _nobank
dw seg _nobank
else
bankadr dw offset _nobank
endif

public vesafunc

vesafunc dw 0
dw 0

vesamodes label word
dw 100h, 640, 400, 8
dw 101h, 640, 480, 8
dw 102h, 800, 600, 4
dw 103h, 800, 600, 8
dw 104h, 1024, 768, 4
dw 105h, 1024, 768, 8
dw 106h, 1280,1024, 4
dw 107h, 1280,1024, 8
dw 10Dh, 320, 200,16
dw 10Eh, 320, 200,16
dw 10Fh, 320, 200,24
dw 110h, 640, 480,16
dw 111h, 640, 480,16
dw 112h, 640, 480,24
dw 113h, 800, 600,16
dw 114h, 800, 600,16
dw 115h, 800, 600,24
dw 116h, 1024, 768,16
dw 117h, 1024, 768,16
dw 118h, 1024, 768,24
dw 119h, 1280,1024,16
dw 11Ah, 1280,1024,16
dw 11Bh, 1280,1024,24
dw 0
.code

public newbank
public whichvga

newbank proc ;bank number is in AX
if @Codesize
jmp dword ptr OSEG[bankadr]
else
jmp OSEG[bankadr]
endif

_tseng:: ;Tseng 3000 series
push ax
push dx
cli
mov OSEG[curbk],ax
and al,7
mov ah,al
shl al,1
shl al,1
shl al,1
or al,ah
or al,01000000b
mov dx,3cdh
out dx,al
sti
pop dx
pop ax
ret


_tseng4:: ;Tseng 4000 series
push ax
push dx
cli
mov OSEG[curbk],ax
mov ah,al
mov dx,3bfh ;Enable access to extended registers
mov al,3
out dx,al
mov dl,0d8h
mov al,0a0h
out dx,al
and ah,15
mov al,ah
shl al,1
shl al,1
shl al,1
shl al,1
or al,ah
mov dl,0cdh
out dx,al
sti
pop dx
pop ax
ret


_trident:: ;Trident
push ax
push dx
push ax
cli
mov OSEG[curbk],ax
mov dx,3ceh ;set pagesize to 64k
mov al,6
out dx,al
inc dl
in al,dx
dec dl
or al,4
mov ah,al
mov al,6
out dx,ax

mov dl,0c4h ;switch to BPS mode
mov al,0bh
out dx,al
inc dl
in al,dx
dec dl

pop ax
mov ah,al
xor ah,2
mov dx,3c4h
mov al,0eh
out dx,ax
sti
pop dx
pop ax
ret


_video7:: ;Video 7
push ax
push dx
push cx
cli
mov OSEG[curbk],ax
and ax,15
mov ch,al
mov dx,3c4h
mov ax,0ea06h
out dx,ax
mov ah,ch
and ah,1
mov al,0f9h
out dx,ax
mov al,ch
and al,1100b
mov ah,al
shr ah,1
shr ah,1
or ah,al
mov al,0f6h
out dx,al
inc dx
in al,dx
dec dx
and al,not 1111b
or ah,al
mov al,0f6h
out dx,ax
mov ah,ch
mov cl,4
shl ah,cl
and ah,100000b
mov dl,0cch
in al,dx
mov dl,0c2h
and al,not 100000b
or al,ah
out dx,al
sti
pop cx
pop dx
pop ax
ret


_paradise:: ;Paradise
push ax
push dx
push ax
cli
mov OSEG[curbk],ax
mov dx,3ceh
mov ax,50fh ;turn off write protect on VGA registers
out dx,ax
pop ax
mov ah,al
mov al,9
out dx,ax
sti
pop dx
pop ax
ret

_acumos:: ;AcuMos
push ax
push dx
push ax
cli
mov OSEG[curbk],ax
mov dx,3c4h ;Sequencer index 6
mov ax,1206h ;turn off write protect on VGA registers
out dx,ax
mov dx,3ceh
pop ax
mov ah,al
mov al,9
out dx,ax
sti
pop dx
pop ax
ret


_chipstech:: ;Chips & Tech
push ax
push dx
push ax
cli
mov OSEG[curbk],ax
mov dx,46e8h ;place chip in setup mode
mov ax,1eh
out dx,ax
mov dx,103h ;enable extended registers
mov ax,0080h
out dx,ax
mov dx,46e8h ;bring chip out of setup mode
mov ax,0eh
out dx,ax
pop ax
mov ah,al
mov al,10h
mov dx,3d6h
out dx,ax
sti
pop dx
pop ax
ret


_ativga:: ;ATI VGA Wonder
push ax
push dx
cli
mov OSEG[curbk],ax
mov ah,al
mov dx,1ceh
mov al,0b2h
out dx,al
inc dl
in al,dx
shl ah,1
and al,0e1h
or ah,al
mov al,0b2h
dec dl
out dx,ax
sti
pop dx
pop ax
ret


_everex:: ;Everex
push ax
push dx
push cx
cli
mov OSEG[curbk],ax
mov cl,al
mov dx,3c4h
mov al,8
out dx,al
inc dl
in al,dx
dec dl
shl al,1
shr cl,1
rcr al,1
mov ah,al
mov al,8
out dx,ax
mov dl,0cch
in al,dx
mov dl,0c2h
and al,0dfh
shr cl,1
jc nob2
or al,20h
nob2: out dx,al
sti
pop cx
pop dx
pop ax
ret


_aheada:: ;Ahead Systems Ver A
push ax
push dx
push cx
cli
mov OSEG[curbk],ax
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
sti
pop cx
pop dx
pop ax
ret


_aheadb:: ;Ahead Systems Ver A
push ax
push dx
push cx
cli
mov OSEG[curbk],ax
mov ch,al
mov dx,3ceh ;Enable extended registers
mov ax,200fh
out dx,ax
mov ah,ch
mov cl,4
shl ah,cl
or ah,ch
mov al,0dh
out dx,ax
sti
pop cx
pop dx
pop ax
ret


_oaktech:: ;Oak Technology Inc OTI-067 and OTI-077
push ax
push dx
cli
mov OSEG[curbk],ax
and al,15
mov ah,al
shl al,1
shl al,1
shl al,1
shl al,1
or ah,al
mov al,11h
mov dx,3deh
out dx,ax
sti
pop dx
pop ax
ret

_genoa:: ;GENOA GVGA
push ax
push dx
cli
mov OSEG[curbk],ax
mov ah,al
shl al,1
shl al,1
shl al,1
or ah,al
mov al,6
or ah,40h
mov dx,3c4h
out dx,ax
sti
pop dx
pop ax
ret

_ncr:: ;NCR 77C22E
push ax
push dx
cli
mov OSEG[curbk],ax
mov ah,al
mov al,18h
mov dx,3c4h
out dx,ax
mov ax,19h
out dx,ax
sti
pop dx
pop ax
ret

_compaq:: ;Compaq
push ax
push dx
push ax
cli
mov OSEG[curbk],ax
mov dx,3ceh
mov ax,50fh ;unlock extended registers
out dx,ax
pop ax
mov ah,al
mov al,45h
out dx,ax
sti
pop dx
pop ax
ret

_vesa:: ;Vesa SVGA interface
push ax
push bx
push dx
cli
mov OSEG[curbk],ax
mov dx,ax
xor bx,bx
call dword ptr OSEG[vesafunc]
mov dx,OSEG[curbk]
mov bx,1
call dword ptr OSEG[vesafunc]
sti
pop dx
pop bx
pop ax
ret

_nobank::
cli
mov OSEG[curbk],ax
sti
ret

newbank endp

bkadr macro func
mov [func],1
mov word ptr [bankadr],offset _&func
if @Codesize
mov word ptr [bankadr+2],seg _&func
endif
endm

nojmp macro
local lbl
jmp lbl
lbl:
endm

dummyvesa proc far
ret
dummyvesa endp

whichvga proc uses si di es
local vesabuf[512]:byte ; extra large to make up for
; bugs in some VESA VBE's

cmp [first],'FI'
jnz gotest
mov ax,[retval]
ret
gotest: mov word ptr [bankadr],offset _nobank
if @Codesize
mov word ptr [bankadr+2],seg _nobank
endif
mov [vgamem],256
mov [bksize],64
xor ax,ax
mov [curbk],ax
mov [cirrus],ax
mov [everex],ax
mov [paradise],ax
mov [tseng],ax
mov [trident],ax
mov [t8900],ax
mov [ativga],ax
mov [aheada],ax
mov [aheadb],ax
mov [oaktech],ax
mov [video7],ax
mov [chipstech],ax
mov [tseng4],ax
mov [genoa],ax
mov [ncr],ax
mov [compaq],ax
mov [vesa],ax
mov [dactype],ax
mov [first],'FI'

cmp [nosvga],0 ;if true abort all SVGA detect code
jz oksvga
mov [retval],ax ;always return zero for no SVGA
ret

oksvga: mov si,1 ;flag for SVGA found

cmp [novesa],0
jz chkvesa
jmp nonvesa
chkvesa:
mov ax,ss
mov es,ax
lea di,vesabuf[0]
mov ax,4f00h
int 10h
cmp ax,4fh
jnz nonvesa
mov [bksize],64 ; (for now)
mov [vesafunc],offset dummyvesa
mov [vesafunc+2],cs
bkadr vesa
mov si,offset vesamodes
cld
vesalp: lodsw
mov cx,ax
jcxz endvesa
mov ax,ss
mov es,ax
lea di,vesabuf[0]
mov ax,4f01h ;is mode available?
int 10h
or ah,ah
jnz notmode
test byte ptr es:[di],1
jz notmode ;if mode not available skip mem size
lodsw
mov cx,ax
lodsw
mov bx,ax
lodsw
mul cx ;multiple by bits per pixel
shr dx,1 ;shift right 3 times to get # of bytes
rcr ax,1
shr dx,1
rcr ax,1
shr dx,1
rcr ax,1
mul bx ;multiply by number of scanlines
mov bx,1024
add ax,bx ;round up to nearest kilobyte
dec ax
adc dx,0
div bx
cmp ax,[vgamem] ;if mode requires more memory
jbe vesalp
mov [vgamem],ax ;increase amount of vga memory
mov ax,vesabuf.vesamode.WinSize
mov [bksize],ax
jmp short vesalp
notmode:
add si,6 ;skip to next mode in list
jmp short vesalp
endvesa:
mov ax,[vgamem]
inc ah
dec ax
mov al,0 ;round up to nearest 256k
cmp ax,1024
jb nomegs
add ax,1023 ;round up to nearest megabyte
and ax,not 1023
nomegs: mov [vgamem],ax

nonvesa:
cmp [justvesa],0
jz nofini
jmp fini ;disable other tests if VESA VBE found

nofini: mov ax,0c000h ;ATI VGA detect (largely from ATI example code)
mov es,ax
cmp word ptr es:[40h],'13' ;ATI Signiture on the Video BIOS
jnz noati
bkadr ativga
mov [bksize],64 ; 64k bank size
mov dx,es:[10h] ; Get value of ATI extended register
mov bl,es:[43h] ; Get value of ATI chip version
cmp bl,'3'
jae v6up ; Use different method to determine
mov al,0bbh ; memory size of chip version is 3 or higher
cli
out dx,al
inc dx
in al,dx ; Get ramsize byte for chip versions 1 & 2
sti
test al,20h
jz no512
mov [vgamem],512
jmp short no512

v6up: mov al,0b0h ; Method used for newer ATI chip versions
cli
out dx,al
inc dx
in al,dx ; Get ramsize byte for versions 3-5
sti
test al,10h ; Check if ramsize byte indicates 256K or 512K bytes
jz v7up
mov [vgamem],512
v7up: cmp bl,'4' ; Check for ramsize for ATI chip versions 4 & 5
jb no512
test al,8 ; Check if version 5 ATI chip has 1024K
jz no512
mov [vgamem],1024
no512: jmp fini

noati: mov ax,7000h ;Test for Everex
xor bx,bx
cld
int 10h
cmp al,70h
jnz noev
bkadr everex
mov [bksize],64 ; 64k bank size
and ch,11000000b ;how much memory on board
jz skp
mov [vgamem],512
skp: ;fall through for Everex boards using Trident or Tseng4000

noev: mov ax,0bf03h ;Test for Compaq
xor bx,bx
mov cx,bx
int 10h
cmp ax,0bf03h
jnz nocp
test cl,40h ;is 640x480x256 available?
jz nocp
bkadr compaq
mov [bksize],4 ; 4k bank size
mov [vgamem],512
jmp fini

nocp: mov dx,3c4h ;Test for NCR 77C22E
mov ax,0ff05h
call _isport2
jnz noncr
mov ax,5 ;Disable extended registers
out dx,ax
mov ax,0ff10h ;Try to write to extended register 10
call _isport2 ;If it writes then not NCR
jz noncr
mov ax,105h ;Enable extended registers
out dx,ax
mov ax,0ff10h
call _isport2
jnz noncr ;If it does NOT write then not NCR
bkadr ncr
mov [bksize],16 ; 16k bank size
mov [vgamem],512
jmp fini

noncr: mov dx,3c4h ;Test for Trident
mov al,0bh
out dx,al
inc dl
in al,dx
and al,0fh
cmp al,06h
ja notri
cmp al,2
jb notri
bkadr trident
mov [bksize],64 ; 64k bank size
cmp al,3
jb no89
mov [t8900],1
mov dx,3d4h
mov al,1fh
out dx,al
inc dx
in al,dx
and ax,3
inc al
xchg al,ah
mov [vgamem],ax
jmp fini

no89: mov [vgamem],512
jmp fini

notri: mov ax,6f00h ;Test for Video 7
xor bx,bx
cld
int 10h
cmp bx,'V7'
jnz nov7
bkadr video7
mov [bksize],64 ; 64k bank size
mov ax,6f07h
cld
int 10h
and ah,7fh
cmp ah,1
jbe skp2
mov [vgamem],512
skp2: cmp ah,3
jbe skp3
mov [vgamem],1024
skp3: jmp fini

nov7: mov dx,3d4h ;Test for GENOA GVGA
mov al,2eh ;check for Herchi Register top 6 bits
out dx,al
inc dx
in al,dx
dec dx
test al,11111100b ;top 6 bits should be zero
jnz nogn
mov ax,032eh ;check for Herchi Register
call _isport2
jnz nogn
mov dx,3c4h
mov al,7
out dx,al
inc dx
in al,dx
dec dx
test al,10001000b
jnz nogn
mov al,10h
out dx,al
inc dx
in al,dx
dec dx
and al,00110000b
cmp al,00100000b
jnz nogn
mov dx,3ceh
mov ax,0ff0bh
call _isport2
jnz nogn
mov dx,3c4h ;check for memory segment register
mov ax,3f06h
call _isport2
jnz nogn
mov dx,3ceh
mov ax,0ff0ah
call _isport2
jnz nogn
bkadr genoa
mov [bksize],64 ; 64k bank size
mov [vgamem],512
jmp fini

nogn: call _cirrus ;Test for Cirrus
cmp [cirrus],0
je noci
jmp fini

noci: mov dx,3ceh ;Test for Paradise
mov al,9 ;check Bank switch register
out dx,al
inc dx
in al,dx
dec dx
or al,al
jnz nopd

mov ax,50fh ;turn off write protect on VGA registers
out dx,ax
mov dx,offset _paradise
mov cx,1
call _chkbk
jc nopd ;if bank 0 and 1 same not paradise
bkadr paradise
mov [bksize],4 ; 4k bank size
mov dx,3ceh
mov al,0bh ;512k detect from Bob Berry
out dx,al
inc dx
in al,dx
test al,80h ;if top bit set then 512k
jz nop512
test al,40h
jz nop1024
mov [vgamem],1024
jmp fini
nop1024:
mov [vgamem],512
nop512: jmp fini

nopd: mov ax,5f00h ;Test for Chips & Tech
xor bx,bx
cld
int 10h
cmp al,5fh
jnz noct
bkadr chipstech
mov [bksize],16 ; 16k bank size
cmp bh,1
jb skp4
mov [vgamem],512
skp4: jmp fini

noct: mov dx,3dah ;Test for Tseng 4000 & 3000
in al,dx ;bit 8 is opposite of bit 4
mov ah,al ;(vertical retrace bit)
shr ah,1
shr ah,1
shr ah,1
shr ah,1
xor al,ah
test al,00001000b
jz nots
mov dx,3d4h ;check for Tseng 4000 series
mov ax,0f33h
call _isport2
jnz not4
mov ax,0ff33h ;top 4 bits should not be there
call _isport2
jz nots

mov dx,3bfh ;Enable access to extended registers
mov al,3
out dx,al
mov dx,3d8h
mov al,0a0h
out dx,al
mov al,0ffh
mov dx,3cdh ;test bank switch register
call _isport1
jnz not4
bkadr tseng
mov [bksize],64 ; 64k bank size
mov ax,10f1h ;Extended BIOS call to get DAC type on Tseng4000
int 10h
cmp ax,10h
jnz nodac
mov bh,0
mov [dactype],bx
nodac: mov dx,3d4h ;Tseng 4000 memory detect 1meg
mov al,37h
out dx,al
inc dx
in al,dx
test al,1000b ;if using 64kx4 RAMs then no more than 256k
jz nomem
and al,3
cmp al,1 ;if 8 bit wide bus then only two 256kx4 RAMs
jbe nomem
mov [vgamem],512
cmp al,2 ;if 16 bit wide bus then four 256kx4 RAMs
je nomem
mov [vgamem],1024 ;full meg with eight 256kx4 RAMs
nomem: bkadr tseng4
mov [bksize],64 ; 64k bank size
jmp fini

not4: mov dx,3d4h ;Test for Tseng 3000
mov ax,1f25h ;is the Overflow High register there?
call _isport2
jnz nots
mov al,03fh ;bottom six bits only
mov dx,3cdh ;test bank switch register
call _isport1
jnz nots
bkadr tseng
mov [bksize],64 ; 64k bank size
call _t3memchk
jmp fini

nots: mov dx,3ceh ;Test for Ahead A or B chipsets
mov ax,0ff0fh ;register should not be fully available
call _isport2
jz noab
mov ax,200fh
out dx,ax
inc dx
nojmp
in al,dx
cmp al,21h
jz verb
cmp al,20h
jnz noab
bkadr aheada
mov [bksize],64 ; 64k bank size
mov [vgamem],512
jmp fini

verb: bkadr aheadb
mov [bksize],64 ; 64k bank size
mov [vgamem],512
jmp fini

noab: mov dx,3c4h ;Test for AcuMos chipsets
mov ax,0006h ;disable extended registers
out dx,ax
mov ax,0ff09h
call _isport2 ;is scratchpad at index 9 writeable ?
jz noacu
mov ax,0ff0ah
call _isport2 ;is scratchpad at index 10 writable ?
jz noacu
mov ax,1206h
out dx,ax
mov ax,0ff09h
call _isport2
jnz noacu
mov ax,0ff0ah
call _isport2
jnz noacu
mov dx,offset _acumos
mov cx,1
call _chkbk
jc noacu ;if bank 0 and 1 same not acumos
bkadr acumos
mov [bksize],4 ; 4k bank size
mov dx,3c4h
mov al,0ah
out dx,al
inc dx
in al,dx ;get scratchpad index 10
and al,3
cmp al,1
jb noamem
mov [vgamem],512
cmp al,2
jb noamem
mov [vgamem],1024
cmp al,3
jb noamem
mov [vgamem],2048
noamem: jmp short fini

noacu: mov dx,3deh ;Test for Oak Technology Inc OTI-067 and OTI-077
mov ax,07711h ;look for bank switch register
call _isport2
jnz nooak
mov al,1ah ;Check from Oak's VESA VBE
out dx,al ;researched by Rick Gould
in al,dx
cmp al,5ah
jz okoak
cmp al,7ah
jnz nooak
okoak: bkadr oaktech
mov [bksize],64 ; 64k bank size
mov al,0dh
out dx,al
inc dx
nojmp
in al,dx
test al,11000000b
jz no4ram
mov [vgamem],512
test al,01000000b
jz no4ram
mov [vgamem],1024
no4ram: jmp short fini

nooak:
mov si,0

fini: cmp [vesa],0
jz novbank
bkadr vesa ; Always use VESA bank switch
; even if we have detected chipset
novbank:
mov ax,si
mov [retval],ax
ret
whichvga endp


;Segment to access video buffer (based on GR[6])
buftbl dw 0A000h,0A000h,0B000h,0B800h

_t3memchk proc ;[Charles Marslett -- ET3000 memory ck]
mov dx,3dah
in al,dx ;Reset the attribute flop (read 0x3DA)
mov dx,03c0h
mov al,36h
out dx,al
inc dx
in al,dx ;Save contents of ATTR[0x16]
push ax
or al,10h
dec dx
out dx,al
mov dx,3ceh ;Find the RAM buffer...
mov al,6
out dx,al
inc dx
in al,dx
and ax,000Ch
shr ax,1

mov bx,ax
push es
mov es,cs:buftbl[bx]
mov ax,09C65h
mov bx,1
mov es:[bx],ax
mov es:[bx+2],ax
inc bx
mov ax,es:[bx]
pop es
cmp ax,0659Ch
jne et3k_256
mov [vgamem],512
et3k_256:
mov dx,3c0h
mov al,36h
out dx,al
pop ax
out dx,al ;Restore ATTR[16h]
ret
_t3memchk endp

_cirrus proc near
mov dx,3d4h ; assume 3dx addressing
mov al,0ch ; screen a start address hi
out dx,al ; select index
inc dx ; point to data
mov ah,al ; save index in ah
in al,dx ; get screen a start address hi
xchg ah,al ; swap index and data
push ax ; save old value
push dx ; save crtc address
xor al,al ; clear crc
out dx,al ; and out to the crtc

mov al,1fh ; Eagle ID register
dec dx ; back to index
out dx,al ; select index
inc dx ; point to data
in al,dx ; read the id register
mov bh,al ; and save it in bh

mov cl,4 ; nibble swap rotate count
mov dx,3c4h ; sequencer/extensions
mov bl,6 ; extensions enable register

ror bh,cl ; compute extensions disable value
mov ax,bx ; extensions disable
out dx,ax ; disable extensions
inc dx ; point to data
in al,dx ; read enable flag
or al,al ; disabled ?
jnz exit ; nope, not an cirrus

ror bh,cl ; compute extensions enable value
dec dx ; point to index
mov ax,bx ; extensions enable
out dx,ax ; enable extensions
inc dx ; point to data
in al,dx ; read enable flag
cmp al,1 ; enabled ?
jne exit ; nope, not an cirrus
mov [cirrus],1
mov word ptr [bankadr],offset _nobank
if @Codesize
mov word ptr [bankadr+2],seg _nobank
endif
exit: pop dx ; restore crtc address
dec dx ; point to index
pop ax ; recover crc index and data
out dx,ax ; restore crc value
ret
_cirrus endp

_chkbk proc near ;bank switch check routine
mov di,0b800h
mov es,di
xor di,di
mov bx,1234h
call _gochk
jnz badchk
mov bx,4321h
call _gochk
jnz badchk
clc
ret
badchk: stc
ret
_chkbk endp

calldx macro
if @Codesize
push cs
endif
call dx
endm

_gochk proc near
push si
mov si,bx

mov al,cl
calldx
xchg bl,es:[di]
mov al,ch
calldx
xchg bh,es:[di]

xchg si,bx

mov al,cl
calldx
xor bl,es:[di]
mov al,ch
calldx
xor bh,es:[di]

xchg si,bx

mov al,ch
calldx
mov es:[di],bh
mov al,cl
calldx
mov es:[di],bl

mov al,0
calldx
or si,si
pop si
ret
_gochk endp

_isport2 proc near ;check for valid indexed i/o port, al is index, ah is bit mask
push bx
mov bx,ax
out dx,al
mov ah,al
inc dx
in al,dx
dec dx
xchg al,ah
push ax
mov ax,bx
out dx,ax
out dx,al
mov ah,al
inc dx
in al,dx
dec dx
and al,bh
cmp al,bh
jnz noport
mov al,ah
mov ah,0
out dx,ax
out dx,al
mov ah,al
inc dx
in al,dx
dec dx
and al,bh
cmp al,0
noport: pop ax
out dx,ax
pop bx
ret
_isport2 endp

_isport1 proc near ;check for valid i/o port, al is bit mask
mov ah,al
in al,dx
push ax
mov al,ah
out dx,al
in al,dx
and al,ah
cmp al,ah
jnz noport
mov al,0
out dx,al
in al,dx
and al,ah
cmp al,0
noport: pop ax
out dx,al
ret
_isport1 endp

end