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hovertank_3d/IDASM.ASM
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hans fb01ea5ba8 first commit
2026-07-14 19:31:07 +02:00

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NASM
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; Hovertank 3-D Source Code
; Copyright (C) 1993-2014 Flat Rock Software
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License along
; with this program; if not, write to the Free Software Foundation, Inc.,
; 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
IDEAL
MODEL SMALL,C
;============================================================================
;
; Gamer's Edge Library, ASM section
;
;============================================================================
;=======================================================================
;
; KEYBOARD ROUTINES
;
;=======================================================================
DATASEG
EVEN
oldint9 dd 0
keydown db 128 dup (0)
NBKscan dw 0
NBKascii dw 0
scanascii db 0,27,49,50,51,52,53,54,55,56,57,48,45,61,8,9,113 ;'q'
db 119,101,114,116,121,117,105,111,112,91,93,13,0,97,115 ;'s'
db 100,102,103,104,106,107,108,59,39,96,0,92,122,120,99 ;'c'
db 118,98,110,109,44,46,47,0,42,0,32,0,1,1,1,1,1,1,1,1,1,1 ;f10
db 0,0,1,1,1,45,1,1,1,43,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0 ;shift-f10
db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ;ctl-home
db 0,0,0,0,0,0,0,0,0,0,0,0,0
PUBLIC keydown,NBKscan,NBKascii
CODESEG
;========
;
; StartupKbd
;
; Sets up the new INT 8 ISR and various internal pointers.
; Assumes that the calling program has pointer soundseg to something
; meaningful...
;
;========
PROC StartupKbd
PUBLIC StartupKbd
mov ax,3509h ;call bios to get int 9
int 21h
mov [WORD oldint9],bx
mov ax,es
mov [WORD oldint9+2],ax
push ds
push cs
pop ds
lea dx,[Int9Isr]
mov ax,2509h ;call bios to set int 9
int 21h
pop ds
ret
ENDP
;========
;
; ShutdownKbd
;
;========
PROC ShutdownKbd
PUBLIC ShutdownKbd
push ds
mov dx,[WORD Oldint9]
mov ds,[WORD Oldint9+2]
mov ax,2509h ;call bios to set int 8
int 21h
mov ax,40h ;clear ctrl/alt/shift flags
mov ds,ax
mov ax,[17h]
and ax,1111110011110000b
mov [17h],ax
pop ds
ret
ENDP
;========
;
; NoBiosKey
;
;========
PROC NoBiosKey parm:WORD
PUBLIC NoBiosKey
xor bh,bh
mov ax,[parm]
or ax,ax
jnz @@bioskey1
@@waitforkey:
mov bl,[BYTE NBKscan]
or bl,bl
jns @@waitforkey
mov al,[BYTE NBKascii]
or al,al
jz @@waitforkey
mov ah,[BYTE NBKscan]
and [BYTE NBKscan],7fh
ret
@@bioskey1:
mov al,[BYTE NBKascii]
mov ah,[BYTE NBKscan]
and ah,7fh
or al,al
jnz @@ok
xor ah,ah ; just a modifier key
@@ok:
ret
ENDP
;========
;
; Int9ISR
; only called by interrupt $9!
;
;=========
PROC Int9ISR FAR
PUBLIC Int9ISR
push ax
push bx
push ds
xor ah,ah
in al,60h ;get the key pressed
push ax
in al,61h
mov ah,al
or al,80h
out 61h,al
mov al,ah
out 61h,al
mov bx,_DATA
mov ds,bx ;ds to this data segment
pop ax
or al,al
jns @@keydown
;
; key released
;
and al,7fh
mov bx,ax
mov [keydown+BX],ah ;keydown[key] = false
jmp @@done
@@keydown:
mov [BYTE NBKscan],al
or [BYTE NBKscan],80h ;high bit set after press, cleared
mov bx,ax ;after NoBiosKey gets it
mov al,1
mov [keydown+BX],al ;keydown[key] = true
mov al,[scanascii+bx]
mov [BYTE NBKascii],al ;set the ascii code of key
@@done:
mov al,20h
out 20h,al ;we got the interrupt here
pop ds
pop bx
pop ax
iret
ENDP
;============================================================================
;
; SOUND ROUTINES
;
;============================================================================
DATASEG
;
;offsets into .SPK file at segment SPKRfile, offset 0
;
;sound records each take up 16 bytes, and start at $10, and continue to $3F0
snd_start equ 0
snd_priority equ 2
snd_samples equ 3
snd_name equ 4
timerspeed dw 0 ;clock speed for tic counting
LABEL inttime WORD
timecount dd 0,0 ;fast timer tics since startup
SPKactive dw 0 ;set non zero when started
soundmode dw 1 ;0=nosound, 1=SPKR, 2= adlib...
OldInt8 dd ? ;StartupSPK saves here, Shutdown restores
Intcount db ? ;counter for extraints, call OldInt8 at 0
SndPtr dw ? ;Pointer to frequency of current sound
SndPriority db ? ;current sound's priority
pausesndptr dw ?
pausepriority db ?
pauseintcount db ?
dontplay dw 0 ;set to 1 to avoid all interrupt and timer stuff
int8hook dw 0 ;gets called every tic if not null
soundseg dw ?
PUBLIC soundmode,dontplay,timecount,inttime,timerspeed,int8hook,soundseg,sndptr
PUBLIC SndPriority
EXTRN soundblaster:WORD
CODESEG
;========
;
; StartupSound
;
; Sets up the new INT 8 ISR and various internal pointers.
; Assumes that the calling program has pointer soundseg to something
; meaningful...
;
;========
PROC StartupSound
PUBLIC StartupSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
test [SPKactive],0FFFFh ;see if library is active
jne @@started ;library was allready started
@@start:
call NEAR PTR StopSound ;make sure nothing is playing
mov ax,3508h ;call bios to get int 8
int 21h
mov [WORD oldint8],bx
mov ax,es
mov [WORD oldint8+2],ax
push ds
push cs
pop ds
lea dx,[UpdateSPKR]
mov ax,2508h ;call bios to set int 8
int 21h
pop ds
mov bx,[timerspeed]
cli
mov al,36h ;tell the timer chip we are going to
out 43h,al ;change the speed of timer 0
mov al,0
mov al,bl
out 40h,al ;low
mov al,bh
out 40h,al ;high
sti
inc [SPKactive] ;sound routines are now active
@@started:
mov ax,1
mov [soundmode],ax ;set soundmode to SPKR
ret
ENDP
;========
;
; CallTimer
;
; Call the bios int8 to turn off drive motors
;
;========
PROC CallTimer
PUBLIC CallTimer
test [WORD OldInt8+2],0ffffh
jz @@done
pushf
call [OldInt8]
@@done:
ret
ENDP
;========
;
; ShutdownSound
;
;========
PROC ShutdownSound
PUBLIC ShutdownSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
cli
mov al,36h ;tell the timer chip we are going to
out 43h,al ;change the speed of timer 0
mov al,0 ;system expects 0000 for rate
out 40h,al ;low
out 40h,al ;high
sti
mov ax,[SPKactive]
cmp ax,0
je @@done ;sound library wasn't started...
push ds
mov dx,[WORD Oldint8]
mov ax,[WORD Oldint8+2]
mov ds,ax
mov ax,2508h ;call bios to set int 8
int 21h
pop ds
mov [SPKactive],0 ;sound routines are now inactive
cli
in al,61h ;get peripheral (speaker) port value
and al,11111101b ;turn speaker off
out 61h,al
sti
@@done:
ret
ENDP
;===========
;
; PlaySoundSPK (soundnum)
;
; If the sound's priority is >= the current priority, SoundPtr, SndPriority,
; and the timer speed are changed
;
; Hacked for sound blaster support!
;
;===========
EXTRN jmPlaySample:PROC
PROC PlaySound playnum:WORD
USES SI
PUBLIC PlaySound
test [dontplay],-1 ;for profiler
jne @@playdone
test [soundmode],-1 ;f2 to turn off sound blaster also
je @@playdone
mov ax,[playnum] ;index into the sound headers
mov si,ax
shl si,1
shl si,1
shl si,1
shl si,1
mov es,[soundseg] ;point es: to the spkr file
mov al,[es:si+snd_Priority] ;priority table (one byte each)
cmp al,[SndPriority]
jb @@playdone ;current sound has higher priority
mov [SndPriority],al
test [soundblaster],-1
jz @@pc
push [playnum]
call jmPlaySample
pop ax
ret
@@pc:
mov ax,[es:si+snd_Start] ;offset in .SPK file
mov [SndPtr],ax ;store it in the sound playing table
@@playdone:
ret
ENDP
;======================================================================
;===========
;
; StopSound
;
;===========
PROC StopSound
PUBLIC StopSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
xor ax,ax ;set to 0
mov [SndPtr],ax
mov [SndPriority],al
cli
in al,61h ;get peripheral (speaker) port value
and al,11111101b ;turn speaker off
out 61h,al
sti
ret
ENDP
;======================================================================
;===========
;
; PauseSound
;
;===========
PROC PauseSound
PUBLIC PauseSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
mov ax,[SndPtr] ;save off the current values
mov [pausesndptr],ax
mov al,[SndPriority]
mov [pausepriority],al
mov al,[intcount]
mov [pauseintcount],al
call StopSound
ret
ENDP
;======================================================================
;===========
;
; ContinueSound
;
;===========
PROC ContinueSound
PUBLIC ContinueSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
mov ax,[pausesndptr]
mov [SndPtr],ax ;restore the old values
mov al,[pausepriority]
mov [SndPriority],al
mov al,[pauseintcount]
mov [intcount],al
ret
ENDP
;======================================================================
;========
;
; WaitendSound
; Just waits around until the current sound stops playing
;
;========
PROC WaitEndSound
PUBLIC WaitEndSound
test [dontplay],0ffffh
je @@dowork
ret
@@dowork:
pushf
call FAR PTR UpdateSPKR ;in case a sound was just started and hasn't
;been hit by an INT yet
@@wait:
mov ax,[sndptr]
cmp ax,0 ;when the ptr is 0, nothing is on
jne @@wait
ret
ENDP
;=========================================================================
;========
;
; UpdateSPKR
; only called by interrupt $8!
;
;=========
DATASEG
EVEN
oldss dw ?
oldsp dw ?
fakestack dw 64 dup (?)
PUBLIC fakestack
CODESEG
PROC UpdateSPKR FAR
PUBLIC UpdateSPKR
push ax
push bx
push cx
push si
push ds
push es
mov al,20h
out 20h,al ;we got the interrupt here
mov ax,@Data
mov ds,ax ;ds to this data segment
add [WORD timecount],1 ;inced once every VBL time
adc [WORD timecount+2],0
;
; call a user routine if needed
;
mov ax,[int8hook]
or ax,ax
jz @@userdone
push ax
push bx
push cx
push dx
push si
push di
push bp
push es
push ds
pushf
mov [oldss],ss ;because we might not be in our stack!
mov [oldsp],sp
mov bx,ds
mov ss,bx ;make SURE the stack is = ds
mov sp,OFFSET fakestack+60
call ax ;user routine that gets called every tic
mov ss,[oldss]
mov sp,[oldsp]
popf
pop ds
pop es
pop bp
pop di
pop si
pop dx
pop cx
pop bx
pop ax
@@userdone:
mov es,[soundseg] ;es to sound file
;
; play the speaker
;
mov si,[SndPtr]
cmp si,0
je @@nosound ;nothing playing
mov bx,[es:si]
inc [SndPtr]
inc [SndPtr]
cmp bx,0
je @@nosound ;a zero frequency is no sound, but don't stop
cmp bx,-1 ;a -1 frequency is end of sound
jne @@playfreq
call StopSound
jmp @@doneplay
@@nosound:
in al,61h ;get peripheral (speaker) port value
and al,11111100b ;turn speaker off
out 61h,al
jmp @@doneplay
@@playfreq:
test [soundmode],0FFh ;if soundon=0, don't play anything
je @@nosound
mov al,10110110b ;write to channel 2 (speaker) timer
out 43h,al
mov al,bl
out 42h,al ;low byte
mov al,bh
out 42h,al ;high byte
in al,61h ;get peripheral (speaker) port value
or al,00000011b ;turn speaker on to timer
out 61h,al
@@doneplay:
pop es
pop ds
pop si
pop cx
pop bx
pop ax
iret
ENDP
;============================================================================
;
; RANDOM ROUTINES
;
;============================================================================
DATASEG
rndindex dw ?
rndtable db 0, 8, 109, 220, 222, 241, 149, 107, 75, 248, 254, 140, 16, 66
db 74, 21, 211, 47, 80, 242, 154, 27, 205, 128, 161, 89, 77, 36
db 95, 110, 85, 48, 212, 140, 211, 249, 22, 79, 200, 50, 28, 188
db 52, 140, 202, 120, 68, 145, 62, 70, 184, 190, 91, 197, 152, 224
db 149, 104, 25, 178, 252, 182, 202, 182, 141, 197, 4, 81, 181, 242
db 145, 42, 39, 227, 156, 198, 225, 193, 219, 93, 122, 175, 249, 0
db 175, 143, 70, 239, 46, 246, 163, 53, 163, 109, 168, 135, 2, 235
db 25, 92, 20, 145, 138, 77, 69, 166, 78, 176, 173, 212, 166, 113
db 94, 161, 41, 50, 239, 49, 111, 164, 70, 60, 2, 37, 171, 75
db 136, 156, 11, 56, 42, 146, 138, 229, 73, 146, 77, 61, 98, 196
db 135, 106, 63, 197, 195, 86, 96, 203, 113, 101, 170, 247, 181, 113
db 80, 250, 108, 7, 255, 237, 129, 226, 79, 107, 112, 166, 103, 241
db 24, 223, 239, 120, 198, 58, 60, 82, 128, 3, 184, 66, 143, 224
db 145, 224, 81, 206, 163, 45, 63, 90, 168, 114, 59, 33, 159, 95
db 28, 139, 123, 98, 125, 196, 15, 70, 194, 253, 54, 14, 109, 226
db 71, 17, 161, 93, 186, 87, 244, 138, 20, 52, 123, 251, 26, 36
db 17, 46, 52, 231, 232, 76, 31, 221, 84, 37, 216, 165, 212, 106
db 197, 242, 98, 43, 39, 175, 254, 145, 190, 84, 118, 222, 187, 136
db 120, 163, 236, 249
;
; Random # Generator vars
;
indexi dw ? ;Rnd#Generator
indexj dw ?
LastRnd dw ?
RndArray dw 17 dup (?)
baseRndArray dw 1,1,2,3,5,8,13,21,54,75,129,204
dw 323,527,850,1377,2227
CODESEG
;=================================================
;
; InitRnd (boolean randomize)
; if randomize is false, the counter is set to 0
;
;=================================================
PROC InitRnd randomize:word
USES SI,DI
public InitRnd
mov ax,ds
mov es,ax
mov di,offset RndArray
mov si,offset baseRndArray
mov cx,17
cld
rep movsw ;set up the table (which is constantly changed)
mov [LastRnd],0
mov [indexi],17*2
mov [indexj],5*2
mov ax,[randomize]
cmp ax,0
je @@setit ;if randomize is true, really random
mov ah,2ch
int 21h ;GetSystemTime
mov [RndArray+34-2],dx
xor dx,cx ;init w/seconds values
mov [RndArray+10-2],dx
@@setit:
mov ax,0ffffh
push ax
call Rnd ;warm up generator!
pop ax
ret
ENDP
;=================================================
;
; unsigned Random (unsigned maxval)
; Return a random # between 0-?
;
;=================================================
PROC Rnd maxval:WORD
USES SI
public Rnd
mov ax,[maxval]
push ax ;save max value
;
; create a mask to cut down on the # of SUBTRACTS!
;
mov dx,0ffffh ;full-mask
@@0:
shl ax,1
jc @@0a
shr dx,1
jmp @@0
@@0a:
mov bx,[indexi] ;this routine was converted from
mov si,[indexj] ;the Random macro on Merlin GS
mov ax,[RndArray-2+bx]
adc ax,[RndArray-2+si]
mov [RndArray-2+bx],ax
add ax,[LastRnd]
mov [LastRnd],ax
dec bx
dec bx
jne @@1
mov bx,17*2
@@1:
dec si
dec si
jne @@2
mov si,17*2
@@2:
mov [indexi],bx
mov [indexj],si
pop cx ;loop -- returns value in range
and ax,dx ;AND our mask!
@@3:
cmp ax,cx ;SUBTRACT to be within range
jbe @@4
shr ax,1
@@4:
ret
ENDP
;=================================================
;
; InitRndT (boolean randomize)
; Init table based RND generator
; if randomize is false, the counter is set to 0
;
;=================================================
PROC InitRndT randomize:word
uses si,di
public initrndt
mov ax,[randomize]
or ax,ax
jne @@timeit ;if randomize is true, really random
mov dx,0 ;set to a definate value
jmp @@setit
@@timeit:
mov ah,2ch
int 21h ;GetSystemTime
and dx,0ffh
@@setit:
mov [rndindex],dx
ret
ENDP
;=================================================
;
; int RandomT (void)
; Return a random # between 0-255
; Exit : AX = value
;
;=================================================
PROC RndT
public RndT
mov bx,[rndindex]
inc bx
and bx,0ffh
mov [rndindex],bx
mov al,[rndtable+BX]
xor ah,ah
ret
ENDP
;============================================================================
;
; MISC VIDEO ROUTINES
;
;============================================================================
;========
;
; WaitVBL (int number)
;
;========
STATUS_REGISTER_1 = 03dah
PROC WaitVBL number:WORD
PUBLIC WaitVBL
mov dx,STATUS_REGISTER_1
mov cx,[number]
waitvbl1:
in al,dx
test al,00001000b ;look for vbl
jnz waitvbl1
waitvbl2:
in al,dx
test al,00001000b ;look for vbl
jz waitvbl2
loop waitvbl1
ret
ENDP
;===========================================================================
MASM
;���������������������������������������������������������
;
; Name: VideoID
;
; Function: Detects the presence of various video subsystems
;
; int VideoID;
;
; Subsystem ID values:
; 0 = (none)
; 1 = MDA
; 2 = CGA
; 3 = EGA
; 4 = MCGA
; 5 = VGA
; 80h = HGC
; 81h = HGC+
; 82h = Hercules InColor
;
;���������������������������������������������������������
;���������������������������������������������������������
;
; Equates
;
;���������������������������������������������������������
VIDstruct STRUC ; corresponds to C data structure
Video0Type DB ? ; first subsystem type
Display0Type DB ? ; display attached to first subsystem
Video1Type DB ? ; second subsystem type
Display1Type DB ? ; display attached to second subsystem
VIDstruct ENDS
Device0 EQU word ptr Video0Type[di]
Device1 EQU word ptr Video1Type[di]
MDA EQU 1 ; subsystem types
CGA EQU 2
EGA EQU 3
MCGA EQU 4
VGA EQU 5
HGC EQU 80h
HGCPlus EQU 81h
InColor EQU 82h
MDADisplay EQU 1 ; display types
CGADisplay EQU 2
EGAColorDisplay EQU 3
PS2MonoDisplay EQU 4
PS2ColorDisplay EQU 5
TRUE EQU 1
FALSE EQU 0
;���������������������������������������������������������
;
; Program
;
;���������������������������������������������������������
Results VIDstruct <> ;results go here!
EGADisplays DB CGADisplay ; 0000b, 0001b (EGA switch values)
DB EGAColorDisplay ; 0010b, 0011b
DB MDADisplay ; 0100b, 0101b
DB CGADisplay ; 0110b, 0111b
DB EGAColorDisplay ; 1000b, 1001b
DB MDADisplay ; 1010b, 1011b
DCCtable DB 0,0 ; translate table for INT 10h func 1Ah
DB MDA,MDADisplay
DB CGA,CGADisplay
DB 0,0
DB EGA,EGAColorDisplay
DB EGA,MDADisplay
DB 0,0
DB VGA,PS2MonoDisplay
DB VGA,PS2ColorDisplay
DB 0,0
DB MCGA,EGAColorDisplay
DB MCGA,PS2MonoDisplay
DB MCGA,PS2ColorDisplay
TestSequence DB TRUE ; this list of flags and addresses
DW FindPS2 ; determines the order in which this
; program looks for the various
EGAflag DB ? ; subsystems
DW FindEGA
CGAflag DB ?
DW FindCGA
Monoflag DB ?
DW FindMono
NumberOfTests EQU ($-TestSequence)/3
PUBLIC VideoID
VideoID PROC near
push bp ; preserve caller registers
mov bp,sp
push ds
push si
push di
push cs
pop ds
ASSUME DS:@Code
; initialize the data structure that will contain the results
lea di,Results ; DS:DI -> start of data structure
mov Device0,0 ; zero these variables
mov Device1,0
; look for the various subsystems using the subroutines whose addresses are
; tabulated in TestSequence; each subroutine sets flags in TestSequence
; to indicate whether subsequent subroutines need to be called
mov byte ptr CGAflag,TRUE
mov byte ptr EGAflag,TRUE
mov byte ptr Monoflag,TRUE
mov cx,NumberOfTests
mov si,offset TestSequence
@@L01: lodsb ; AL := flag
test al,al
lodsw ; AX := subroutine address
jz @@L02 ; skip subroutine if flag is false
push si
push cx
call ax ; call subroutine to detect subsystem
pop cx
pop si
@@L02: loop @@L01
; determine which subsystem is active
call FindActive
mov al,Results.Video0Type
mov ah,0 ; was: Results.Display0Type
pop di ; restore caller registers and return
pop si
pop ds
mov sp,bp
pop bp
ret
VideoID ENDP
;
; FindPS2
;
; This subroutine uses INT 10H function 1Ah to determine the video BIOS
; Display Combination Code (DCC) for each video subsystem present.
;
FindPS2 PROC near
mov ax,1A00h
int 10h ; call video BIOS for info
cmp al,1Ah
jne @@L13 ; exit if function not supported (i.e.,
; no MCGA or VGA in system)
; convert BIOS DCCs into specific subsystems & displays
mov cx,bx
xor bh,bh ; BX := DCC for active subsystem
or ch,ch
jz @@L11 ; jump if only one subsystem present
mov bl,ch ; BX := inactive DCC
add bx,bx
mov ax,[bx+offset DCCtable]
mov Device1,ax
mov bl,cl
xor bh,bh ; BX := active DCC
@@L11: add bx,bx
mov ax,[bx+offset DCCtable]
mov Device0,ax
; reset flags for subsystems that have been ruled out
mov byte ptr CGAflag,FALSE
mov byte ptr EGAflag,FALSE
mov byte ptr Monoflag,FALSE
lea bx,Video0Type[di] ; if the BIOS reported an MDA ...
cmp byte ptr [bx],MDA
je @@L12
lea bx,Video1Type[di]
cmp byte ptr [bx],MDA
jne @@L13
@@L12: mov word ptr [bx],0 ; ... Hercules can't be ruled out
mov byte ptr Monoflag,TRUE
@@L13: ret
FindPS2 ENDP
;
; FindEGA
;
; Look for an EGA. This is done by making a call to an EGA BIOS function
; which doesn't exist in the default (MDA, CGA) BIOS.
FindEGA PROC near ; Caller: AH = flags
; Returns: AH = flags
; Video0Type and
; Display0Type updated
mov bl,10h ; BL := 10h (return EGA info)
mov ah,12h ; AH := INT 10H function number
int 10h ; call EGA BIOS for info
; if EGA BIOS is present,
; BL <> 10H
; CL = switch setting
cmp bl,10h
je @@L22 ; jump if EGA BIOS not present
mov al,cl
shr al,1 ; AL := switches/2
mov bx,offset EGADisplays
xlat ; determine display type from switches
mov ah,al ; AH := display type
mov al,EGA ; AL := subystem type
call FoundDevice
cmp ah,MDADisplay
je @@L21 ; jump if EGA has a monochrome display
mov CGAflag,FALSE ; no CGA if EGA has color display
jmp short @@L22
@@L21: mov Monoflag,FALSE ; EGA has a mono display, so MDA and
; Hercules are ruled out
@@L22: ret
FindEGA ENDP
;
; FindCGA
;
; This is done by looking for the CGA's 6845 CRTC at I/O port 3D4H.
;
FindCGA PROC near ; Returns: VIDstruct updated
mov dx,3D4h ; DX := CRTC address port
call Find6845
jc @@L31 ; jump if not present
mov al,CGA
mov ah,CGADisplay
call FoundDevice
@@L31: ret
FindCGA ENDP
;
; FindMono
;
; This is done by looking for the MDA's 6845 CRTC at I/O port 3B4H. If
; a 6845 is found, the subroutine distinguishes between an MDA
; and a Hercules adapter by monitoring bit 7 of the CRT Status byte.
; This bit changes on Hercules adapters but does not change on an MDA.
;
; The various Hercules adapters are identified by bits 4 through 6 of
; the CRT Status value:
;
; 000b = HGC
; 001b = HGC+
; 101b = InColor card
;
FindMono PROC near ; Returns: VIDstruct updated
mov dx,3B4h ; DX := CRTC address port
call Find6845
jc @@L44 ; jump if not present
mov dl,0BAh ; DX := 3BAh (status port)
in al,dx
and al,80h
mov ah,al ; AH := bit 7 (vertical sync on HGC)
mov cx,8000h ; do this 32768 times
@@L41: in al,dx
and al,80h ; isolate bit 7
cmp ah,al
loope @@L41 ; wait for bit 7 to change
jne @@L42 ; if bit 7 changed, it's a Hercules
mov al,MDA ; if bit 7 didn't change, it's an MDA
mov ah,MDADisplay
call FoundDevice
jmp short @@L44
@@L42: in al,dx
mov dl,al ; DL := value from status port
and dl,01110000b ; mask bits 4 thru 6
mov ah,MDADisplay ; assume it's a monochrome display
mov al,HGCPlus ; look for an HGC+
cmp dl,00010000b
je @@L43 ; jump if it's an HGC+
mov al,HGC ; look for an InColor card or HGC
cmp dl,01010000b
jne @@L43 ; jump if it's not an InColor card
mov al,InColor ; it's an InColor card
mov ah,EGAColorDisplay
@@L43: call FoundDevice
@@L44: ret
FindMono ENDP
;
; Find6845
;
; This routine detects the presence of the CRTC on a MDA, CGA or HGC.
; The technique is to write and read register 0Fh of the chip (cursor
; low). If the same value is read as written, assume the chip is
; present at the specified port addr.
;
Find6845 PROC near ; Caller: DX = port addr
; Returns: cf set if not present
mov al,0Fh
out dx,al ; select 6845 reg 0Fh (Cursor Low)
inc dx
in al,dx ; AL := current Cursor Low value
mov ah,al ; preserve in AH
mov al,66h ; AL := arbitrary value
out dx,al ; try to write to 6845
mov cx,100h
@@L51: loop @@L51 ; wait for 6845 to respond
in al,dx
xchg ah,al ; AH := returned value
; AL := original value
out dx,al ; restore original value
cmp ah,66h ; test whether 6845 responded
je @@L52 ; jump if it did (cf is reset)
stc ; set carry flag if no 6845 present
@@L52: ret
Find6845 ENDP
;
; FindActive
;
; This subroutine stores the currently active device as Device0. The
; current video mode determines which subsystem is active.
;
FindActive PROC near
cmp word ptr Device1,0
je @@L63 ; exit if only one subsystem
cmp Video0Type[di],4 ; exit if MCGA or VGA present
jge @@L63 ; (INT 10H function 1AH
cmp Video1Type[di],4 ; already did the work)
jge @@L63
mov ah,0Fh
int 10h ; AL := current BIOS video mode
and al,7
cmp al,7 ; jump if monochrome
je @@L61 ; (mode 7 or 0Fh)
cmp Display0Type[di],MDADisplay
jne @@L63 ; exit if Display0 is color
jmp short @@L62
@@L61: cmp Display0Type[di],MDADisplay
je @@L63 ; exit if Display0 is monochrome
@@L62: mov ax,Device0 ; make Device0 currently active
xchg ax,Device1
mov Device0,ax
@@L63: ret
FindActive ENDP
;
; FoundDevice
;
; This routine updates the list of subsystems.
;
FoundDevice PROC near ; Caller: AH = display #
; AL = subsystem #
; Destroys: BX
lea bx,Video0Type[di]
cmp byte ptr [bx],0
je @@L71 ; jump if 1st subsystem
lea bx,Video1Type[di] ; must be 2nd subsystem
@@L71: mov [bx],ax ; update list entry
ret
FoundDevice ENDP
END
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