Cream of the Crop 1/Cream of the Crop 1.iso/PROGRAM/VGAKIT50.ARJ/BANKS.ASM

Assembly Source File | 1992-06-25 | 17KB | 1,059 lines

    include    model.h
    include    vesa.h
;
;    VGAKIT Version 5.0
;
;    Copyright 1988,89,90,91,92 John Bridges
;    Free for use in commercial, shareware or freeware applications
;
;    BANKS.ASM
;
.data

OSEG    equ    DS:        ;segment override for variable access

    public    bankadr

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

    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

    public    cirrus,everex,acumos,paradise,tseng,trident,t8900
    public    ativga,aheada,aheadb,oaktech,video7
    public    chipstech,tseng4,genoa,ncr,compaq,s3vga,vesa

cirrus    dw    ?
everex    dw    ?
acumos    dw    ?
paradise dw    ?
tseng    dw    ?
trident    dw    ?
t8900    dw    ?
ativga    dw    ?
aheada    dw    ?
aheadb    dw    ?
oaktech    dw    ?
video7    dw    ?
chipstech dw    ?
tseng4    dw    ?
genoa    dw    ?
ncr    dw    ?
compaq    dw    ?
s3vga    dw    ?
vesa    dw    ?

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

.code

    public    newbank
    public    whichvga

newbank    proc            ;bank number is in AX
    jmp    OSEG[bankadr]


_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

_s3vga::            ;S3 VGA
    push    ax
    push    dx
    cli
    mov    OSEG[curbk],ax
    sti
    pop    dx
    pop    ax
    ret

_vesa::                ;Vesa SVGA interface
    push    ax
    push    bx
    push    cx
    push    dx
    cli
    mov    OSEG[curbk],ax
    mov    dx,ax
    xor    bx,bx
    mov    ax,4f05h
    int    10h
    sti
    pop    dx
    pop    cx
    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


whichvga proc    uses si di
    local    vesabuf[256]:byte

    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    [s3vga],ax
    mov    [vesa],ax
    mov    [first],'FI'

    mov    si,1            ;flag for SVGA found

    mov    ax,ss
    mov    es,ax
    lea    di,vesabuf[0]
    mov    ax,4f00h
    int    10h
    cmp    ax,4fh
    jnz    novesa
    bkadr    vesa
    mov    [bksize],64        ; (for now)

novesa:    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,3d5h
    mov    al,1fh
    out    dx,al
    inc    dx
    in    al,dx
    and    al,3
    cmp    al,1
    jb    notmem
    mov    [vgamem],512
    je    notmem
    mov    [vgamem],1024
notmem:    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    ax,032eh        ;check for Herchi Register
    call    _isport2
    jnz    nogn
    mov    dx,3c4h            ;check for memory segment register
    mov    ax,3f06h
    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
    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    ch,0
    mov    dx,3d4h            ;check for Tseng 4000 series
    mov    ax,0f33h
    call    _isport2
    jnz    not4
    mov    ch,1

    mov    dx,3bfh            ;Enable access to extended registers
    mov    al,3
    out    dx,al
    mov    dx,3d8h
    mov    al,0a0h
    out    dx,al
    jmp    short yes4

not4:    mov    dx,3d4h            ;Test for Tseng 3000 or 4000
    mov    ax,1f25h        ;is the Overflow High register there?
    call    _isport2
    jnz    nots
    mov    al,03fh            ;bottom six bits only
    jmp    short yes3
yes4:    mov    al,0ffh
yes3:    mov    dx,3cdh            ;test bank switch register
    call    _isport1
    jnz    nots
    bkadr    tseng
    mov    [bksize],64        ; 64k bank size
    cmp    ch,0
    jnz    t4mem
    mov    [vgamem],512
    jmp    fini

t4mem:    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

nots:    mov    dx,3ceh            ;Test for Above A or B chipsets
    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
    mov    ax,0ff11h        ;look for bank switch register
    call    _isport2
    jnz    nooak
    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:    jmp    short nos3
    bkadr    s3vga
    mov    [bksize],64        ; 64k bank size
    mov    [vgamem],1024
    jmp    short fini

nos3:    cmp    [vesa],0
    jz    nosvga
    mov    [vgamem],2048
    jmp    short fini

nosvga:    mov    si,0

fini:    mov    ax,si
    mov    [retval],ax
    ret
whichvga 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