Microsoft Programmer's Library 1.3

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Assembly Source File | 1988-08-11 | 38.6 KB | 1,080 lines

; ; Name: snap ; ; Description: This RAM-resident (terminate-and-stay-resident) utility ; produces a video "snapshot" by copying the contents of the ; video regeneration buffer to a disk file. It may be used ; in 80-column alphanumeric video modes on IBM PCs and PS/2s. ; ; Comments: Assemble and link to create SNAP.EXE. ; ; Execute SNAP.EXE to make resident. ; ; Press Alt-Enter to dump current contents of video buffer ; to a disk file. ; MultiplexID EQU 0CAh ; unique INT 2FH ID value TSRStackSize EQU 100h ; resident stack size in bytes KB_FLAG EQU 17h ; offset of shift-key status flag in ; ROM BIOS keyboard data area KBIns EQU 80h ; bit masks for KB_FLAG KBCaps EQU 40h KBNum EQU 20h KBScroll EQU 10h KBAlt EQU 8 KBCtl EQU 4 KBLeft EQU 2 KBRight EQU 1 SCEnter EQU 1Ch CR EQU 0Dh LF EQU 0Ah TRUE EQU -1 FALSE EQU 0 PAGE ;------------------------------------------------------------------------------ ; ; RAM-resident routines ; ;------------------------------------------------------------------------------ RESIDENT_GROUP GROUP RESIDENT_TEXT,RESIDENT_DATA,RESIDENT_STACK RESIDENT_TEXT SEGMENT byte public 'CODE' ASSUME cs:RESIDENT_GROUP,ds:RESIDENT_GROUP ;------------------------------------------------------------------------------ ; System verification routines ;------------------------------------------------------------------------------ VerifyDOSState PROC near ; Returns: carry flag set if MS-DOS ; is busy push ds ; preserve these registers push bx push ax lds bx,cs:ErrorModeAddr mov ah,[bx] ; AH = ErrorMode flag lds bx,cs:InDOSAddr mov al,[bx] ; AL = InDOS flag xor bx,bx ; BH = 00H, BL = 00H cmp bl,cs:InISR28 ; carry flag set if INT 28H handler ; is running rcl bl,01h ; BL = 01H if INT 28H handler is running cmp bx,ax ; carry flag zero if AH = 00H ; and AL <= BL pop ax ; restore registers pop bx pop ds ret VerifyDOSState ENDP VerifyIntState PROC near ; Returns: carry flag set if hardware ; or ROM BIOS unstable push ax ; preserve AX ; Verify hardware interrupt status by interrogating Intel 8259A Programmable ; Interrupt Controller mov ax,00001011b ; AH = 0 ; AL = 0CW3 for Intel 8259A (RR = 1, ; RIS = 1) out 20h,al ; request 8259A's in-service register jmp short L10 ; wait a few cycles L10: in al,20h ; AL = hardware interrupts currently ; being serviced (bit = 1 if in-service) cmp ah,al jc L11 ; exit if any hardware interrupts still ; being serviced ; Verify status of ROM BIOS interrupt handlers xor al,al ; AL = 00H cmp al,cs:InISR5 jc L11 ; exit if currently in INT 05H handler cmp al,cs:InISR9 jc L11 ; exit if currently in INT 09H handler cmp al,cs:InISR10 jc L11 ; exit if currently in INT 10H handler cmp al,cs:InISR13 ; set carry flag if currently in ; INT 13H handler L11: pop ax ; restore AX and return ret VerifyIntState ENDP VerifyTSRState PROC near ; Returns: carry flag set if TSR ; inactive rol cs:HotFlag,1 ; carry flag set if (HotFlag = TRUE) cmc ; carry flag set if (HotFlag = FALSE) jc L20 ; exit if no hot key ror cs:ActiveTSR,1 ; carry flag set if (ActiveTSR = TRUE) jc L20 ; exit if already active call VerifyDOSState jc L20 ; exit if MS-DOS unstable call VerifyIntState ; set carry flag if hardware or BIOS ; unstable L20: ret VerifyTSRState ENDP PAGE ;------------------------------------------------------------------------------ ; System monitor routines ;------------------------------------------------------------------------------ ISR5 PROC far ; INT 05H handler ; (ROM BIOS print screen) inc cs:InISR5 ; increment status flag pushf cli call cs:PrevISR5 ; chain to previous INT 05H handler dec cs:InISR5 ; decrement status flag iret ISR5 ENDP ISR8 PROC far ; INT 08H handler (timer tick, IRQ0) pushf cli call cs:PrevISR8 ; chain to previous handler cmp cs:InISR8,0 jne L31 ; exit if already in this handler inc cs:InISR8 ; increment status flag sti ; interrupts are ok call VerifyTSRState jc L30 ; jump if TSR is inactive mov byte ptr cs:ActiveTSR,TRUE call TSRapp mov byte ptr cs:ActiveTSR,FALSE L30: dec cs:InISR8 L31: iret ISR8 ENDP ISR9 PROC far ; INT 09H handler ; (keyboard interrupt IRQ1) push ds ; preserve these registers push ax push bx push cs pop ds ; DS -> RESIDENT_GROUP in al,60h ; AL = current scan code pushf ; simulate an INT cli call ds:PrevISR9 ; let previous handler execute mov ah,ds:InISR9 ; if already in this handler .. or ah,ds:HotFlag ; .. or currently processing hot key .. jnz L43 ; .. jump to exit inc ds:InISR9 ; increment status flag sti ; now interrupts are ok ; Check scan code sequence cmp ds:HotSeqLen,0 je L40 ; jump if no hot sequence to match mov bx,ds:HotIndex cmp al,[bx+HotSequence] ; test scan code sequence jne L41 ; jump if no match inc bx cmp bx,ds:HotSeqLen jb L42 ; jump if not last scan code to match ; Check shift-key state L40: push ds mov ax,40h mov ds,ax ; DS -> ROM BIOS data area mov al,ds:[KB_FLAG] ; AH = ROM BIOS shift-key flags pop ds and al,ds:HotKBMask ; AL = flags AND "don't care" mask cmp al,ds:HotKBFlag jne L42 ; jump if shift state does not match ; Set flag when hot key is found mov byte ptr ds:HotFlag,TRUE L41: xor bx,bx ; reinitialize index L42: mov ds:HotIndex,bx ; update index into sequence dec ds:InISR9 ; decrement status flag L43: pop bx ; restore registers and exit pop ax pop ds iret ISR9 ENDP ISR10 PROC far ; INT 10H handler (ROM BIOS video I/O) inc cs:InISR10 ; increment status flag pushf cli call cs:PrevISR10 ; chain to previous INT 10H handler dec cs:InISR10 ; decrement status flag iret ISR10 ENDP ISR13 PROC far ; INT 13H handler ; (ROM BIOS fixed disk I/O) inc cs:InISR13 ; increment status flag pushf cli call cs:PrevISR13 ; chain to previous INT 13H handler pushf ; preserve returned flags dec cs:InISR13 ; decrement status flag popf ; restore flags register sti ; enable interrupts ret 2 ; simulate IRET without popping flags ISR13 ENDP ISR1B PROC far ; INT 1BH trap (ROM BIOS Ctrl-Break) mov byte ptr cs:Trap1B,TRUE iret ISR1B ENDP ISR23 PROC far ; INT 23H trap (MS-DOS Ctrl-C) mov byte ptr cs:Trap23,TRUE iret ISR23 ENDP ISR24 PROC far ; INT 24H trap (MS-DOS critical error) mov byte ptr cs:Trap24,TRUE xor al,al ; AL = 00H (MS-DOS 2.x): ; ignore the error cmp cs:MajorVersion,2 je L50 mov al,3 ; AL = 03H (MS-DOS 3.x): ; fail the MS-DOS call in which ; the critical error occurred L50: iret ISR24 ENDP ISR28 PROC far ; INT 28H handler ; (MS-DOS idle interrupt) pushf cli call cs:PrevISR28 ; chain to previous INT 28H handler cmp cs:InISR28,0 jne L61 ; exit if already inside this handler inc cs:InISR28 ; increment status flag call VerifyTSRState jc L60 ; jump if TSR is inactive mov byte ptr cs:ActiveTSR,TRUE call TSRapp mov byte ptr cs:ActiveTSR,FALSE L60: dec cs:InISR28 ; decrement status flag L61: iret ISR28 ENDP ISR2F PROC far ; INT 2FH handler ; (MS-DOS multiplex interrupt) ; Caller: AH = handler ID ; AL = function number ; Returns for function 0: AL = 0FFH ; for all other functions: nothing cmp ah,MultiplexID je L70 ; jump if this handler is requested jmp cs:PrevISR2F ; chain to previous INT 2FH handler L70: test al,al jnz MultiplexIRET ; jump if reserved or undefined function ; Function 0: get installed state mov al,0FFh ; AL = 0FFh (this handler is installed) MultiplexIRET: iret ; return from interrupt ISR2F ENDP PAGE ; ; ; AuxInt21--sets ErrorMode while executing INT 21h to force use of the ; AuxStack instead of the IOStack. ; ; AuxInt21 PROC near ; Caller: registers for INT 21H ; Returns: registers from INT 21H push ds push bx lds bx,ErrorModeAddr inc byte ptr [bx] ; ErrorMode is now nonzero pop bx pop ds int 21h ; perform MS-DOS function push ds push bx lds bx,ErrorModeAddr dec byte ptr [bx] ; restore ErrorMode pop bx pop ds ret AuxInt21 ENDP Int21v PROC near ; perform INT 21H or AuxInt21, ; depending on MS-DOS version cmp DOSVersion,30Ah jb L80 ; jump if earlier than 3.1 int 21h ; version 3.1 and later ret L80: call AuxInt21 ; versions earlier than 3.1 ret Int21v ENDP PAGE ;------------------------------------------------------------------------------ ; RAM-resident application ;------------------------------------------------------------------------------ TSRapp PROC near ; Set up a safe stack push ds ; save previous DS on previous stack push cs pop ds ; DS -> RESIDENT_GROUP mov PrevSP,sp ; save previous SS:SP mov PrevSS,ss mov ss,TSRSS ; SS:SP -> RESIDENT_STACK mov sp,TSRSP push es ; preserve remaining registers push ax push bx push cx push dx push si push di push bp cld ; clear direction flag ; Set break and critical error traps mov cx,NTrap mov si,offset RESIDENT_GROUP:StartTrapList L90: lodsb ; AL = interrupt number ; DS:SI -> byte past interrupt number mov byte ptr [si],FALSE ; zero the trap flag push ax ; preserve AX mov ah,35h ; INT 21H function 35H ; (get interrupt vector) int 21h ; ES:BX = previous interrupt vector mov [si+1],bx ; save offset and segment .. mov [si+3],es ; .. of previous handler pop ax ; AL = interrupt number mov dx,[si+5] ; DS:DX -> this TSR's trap mov ah,25h ; INT 21H function 25H int 21h ; (set interrupt vector) add si,7 ; DS:SI -> next in list loop L90 ; Disable MS-DOS break checking during disk I/O mov ax,3300h ; AH = INT 21H function number ; AL = 00H (request current break state) int 21h ; DL = current break state mov PrevBreak,dl ; preserve current state xor dl,dl ; DL = 00H (disable disk I/O break ; checking) mov ax,3301h ; AL = 01H (set break state) int 21h ; Preserve previous extended error information cmp DOSVersion,30Ah jb L91 ; jump if MS-DOS version earlier ; than 3.1 push ds ; preserve DS xor bx,bx ; BX = 00H (required for function 59H) mov ah,59h ; INT 21H function 59H call Int21v ; (get extended error info) mov cs:PrevExtErrDS,ds pop ds mov PrevExtErrAX,ax ; preserve error information mov PrevExtErrBX,bx ; in data structure mov PrevExtErrCX,cx mov PrevExtErrDX,dx mov PrevExtErrSI,si mov PrevExtErrDI,di mov PrevExtErrES,es ; Inform MS-DOS about current PSP L91: mov ah,51h ; INT 21H function 51H (get PSP address) call Int21v ; BX = foreground PSP mov PrevPSP,bx ; preserve previous PSP mov bx,TSRPSP ; BX = resident PSP mov ah,50h ; INT 21H function 50H (set PSP address) call Int21v ; Inform MS-DOS about current DTA (not really necessary in this application ; because DTA is not used) mov ah,2Fh ; INT 21H function 2FH int 21h ; (get DTA address) into ES:BX mov PrevDTAoffs,bx mov PrevDTAseg,es push ds ; preserve DS mov ds,TSRPSP mov dx,80h ; DS:DX -> default DTA at PSP:0080 mov ah,1Ah ; INT 21H function 1AH int 21h ; (set DTA address) pop ds ; restore DS ; Open a file, write to it, and close it mov ax,0E07h ; AH = INT 10H function number ; (Write Teletype) ; AL = 07H (bell character) int 10h ; emit a beep mov dx,offset RESIDENT_GROUP:SnapFile mov ah,3Ch ; INT 21H function 3CH ; (create file handle) mov cx,0 ; file attribute int 21h jc L94 ; jump if file not opened push ax ; push file handle mov ah,0Fh ; INT 10H function 0FH ; (get video status) int 10h ; AL = video mode number ; AH = number of character columns pop bx ; BX = file handle cmp ah,80 jne L93 ; jump if not 80-column mode mov dx,0B800h ; DX = color video buffer segment cmp al,3 jbe L92 ; jump if color alphanumeric mode cmp al,7 jne L93 ; jump if not monochrome mode mov dx,0B000h ; DX = monochrome video buffer segment L92: push ds mov ds,dx xor dx,dx ; DS:DX -> start of video buffer mov cx,80*25*2 ; CX = number of bytes to write mov ah,40h ; INT 21H function 40H (write file) int 21h pop ds L93: mov ah,3Eh ; INT 21H function 3EH (close file) int 21h mov ax,0E07h ; emit another beep int 10h ; Restore previous DTA L94: push ds ; preserve DS lds dx,PrevDTA ; DS:DX -> previous DTA mov ah,1Ah ; INT 21H function 1AH (set DTA address) int 21h pop ds ; Restore previous PSP mov bx,PrevPSP ; BX = previous PSP mov ah,50h ; INT 21H function 50H call Int21v ; (set PSP address) ; Restore previous extended error information mov ax,DOSVersion cmp ax,30AH jb L95 ; jump if MS-DOS version earlier than 3.1 cmp ax,0A00h jae L95 ; jump if MS OS/2-DOS 3.x box mov dx,offset RESIDENT_GROUP:PrevExtErrInfo mov ax,5D0Ah int 21h ; (restore extended error information) ; Restore previous MS-DOS break checking L95: mov dl,PrevBreak ; DL = previous state mov ax,3301h int 21h ; Restore previous break and critical error traps mov cx,NTrap mov si,offset RESIDENT_GROUP:StartTrapList push ds ; preserve DS L96: lods byte ptr cs:[si] ; AL = interrupt number ; ES:SI -> byte past interrupt number lds dx,cs:[si+1] ; DS:DX -> previous handler mov ah,25h ; INT 21H function 25H int 21h ; (set interrupt vector) add si,7 ; DS:SI -> next in list loop L96 pop ds ; restore DS ; Restore all registers pop bp pop di pop si pop dx pop cx pop bx pop ax pop es mov ss,PrevSS ; SS:SP -> previous stack mov sp,PrevSP pop ds ; restore previous DS ; Finally, reset status flag and return mov byte ptr cs:HotFlag,FALSE ret TSRapp ENDP RESIDENT_TEXT ENDS RESIDENT_DATA SEGMENT word public 'DATA' ErrorModeAddr DD ? ; address of MS-DOS ErrorMode flag InDOSAddr DD ? ; address of MS-DOS InDOS flag NISR DW (EndISRList-StartISRList)/8 ; number of installed ISRs StartISRList DB 05h ; INT number InISR5 DB FALSE ; flag PrevISR5 DD ? ; address of previous handler DW offset RESIDENT_GROUP:ISR5 DB 08h InISR8 DB FALSE PrevISR8 DD ? DW offset RESIDENT_GROUP:ISR8 DB 09h InISR9 DB FALSE PrevISR9 DD ? DW offset RESIDENT_GROUP:ISR9 DB 10h InISR10 DB FALSE PrevISR10 DD ? DW offset RESIDENT_GROUP:ISR10 DB 13h InISR13 DB FALSE PrevISR13 DD ? DW offset RESIDENT_GROUP:ISR13 DB 28h InISR28 DB FALSE PrevISR28 DD ? DW offset RESIDENT_GROUP:ISR28 DB 2Fh InISR2F DB FALSE PrevISR2F DD ? DW offset RESIDENT_GROUP:ISR2F EndISRList LABEL BYTE TSRPSP DW ? ; resident PSP TSRSP DW TSRStackSize ; resident SS:SP TSRSS DW seg RESIDENT_STACK PrevPSP DW ? ; previous PSP PrevSP DW ? ; previous SS:SP PrevSS DW ? HotIndex DW 0 ; index of next scan code in sequence HotSeqLen DW EndHotSeq-HotSequence ; length of hot-key sequence HotSequence DB SCEnter ; hot sequence of scan codes EndHotSeq LABEL BYTE HotKBFlag DB KBAlt ; hot value of ROM BIOS KB_FLAG HotKBMask DB (KBIns OR KBCaps OR KBNum OR KBScroll) XOR 0FFh HotFlag DB FALSE ActiveTSR DB FALSE DOSVersion LABEL WORD DB ? ; minor version number MajorVersion DB ? ; major version number ; The following data is used by the TSR application: NTrap DW (EndTrapList-StartTrapList)/8 ; number of traps StartTrapList DB 1Bh Trap1B DB FALSE PrevISR1B DD ? DW offset RESIDENT_GROUP:ISR1B DB 23h Trap23 DB FALSE PrevISR23 DD ? DW offset RESIDENT_GROUP:ISR23 DB 24h Trap24 DB FALSE PrevISR24 DD ? DW offset RESIDENT_GROUP:ISR24 EndTrapList LABEL BYTE PrevBreak DB ? ; previous break-checking flag PrevDTA LABEL DWORD ; previous DTA address PrevDTAoffs DW ? PrevDTAseg DW ? PrevExtErrInfo LABEL BYTE ; previous extended error information PrevExtErrAX DW ? PrevExtErrBX DW ? PrevExtErrCX DW ? PrevExtErrDX DW ? PrevExtErrSI DW ? PrevExtErrDI DW ? PrevExtErrDS DW ? PrevExtErrES DW ? DW 3 dup(0) SnapFile DB '\snap.img' ; output filename in root directory RESIDENT_DATA ENDS RESIDENT_STACK SEGMENT word stack 'STACK' DB TSRStackSize dup(?) RESIDENT_STACK ENDS PAGE ;------------------------------------------------------------------------------ ; ; Transient installation routines ; ;------------------------------------------------------------------------------ TRANSIENT_TEXT SEGMENT para public 'TCODE' ASSUME cs:TRANSIENT_TEXT,ds:RESIDENT_DATA,ss:RESIDENT_STACK InstallSnapTSR PROC far ; At entry: CS:IP -> InstallSnapTSR ; SS:SP -> stack ; DS,ES -> PSP ; Save PSP segment mov ax,seg RESIDENT_DATA mov ds,ax ; DS -> RESIDENT_DATA mov TSRPSP,es ; save PSP segment ; Check the MS-DOS version call GetDOSVersion ; AH = major version number ; AL = minor version number ; Verify that this TSR is not already installed ; ; Before executing INT 2Fh in MS-DOS versions 2.x, test whether INT 2FH ; vector is in use. If so, abort if PRINT.COM is using it. ; ; (Thus, in MS-DOS 2.x, if both this program and PRINT.COM are used, ; this program should be made resident before PRINT.COM.) cmp ah,2 ja L101 ; jump if version 3.0 or later mov ax,352Fh ; AH = INT 21H function number ; AL = interrupt number int 21h ; ES:BX = INT 2FH vector mov ax,es or ax,bx ; jump if current INT 2FH vector .. jnz L100 ; .. is nonzero push ds mov ax,252Fh ; AH = INT 21H function number ; AL = interrupt number mov dx,seg RESIDENT_GROUP mov ds,dx mov dx,offset RESIDENT_GROUP:MultiplexIRET int 21h ; point INT 2FH vector to IRET pop ds jmp short L103 ; jump to install this TSR L100: mov ax,0FF00h ; look for PRINT.COM: int 2Fh ; if resident, AH = print queue length; ; otherwise, AH is unchanged cmp ah,0FFh ; if PRINT.COM is not resident .. je L101 ; .. use multiplex interrupt mov al,1 call FatalError ; abort if PRINT.COM already installed L101: mov ah,MultiplexID ; AH = multiplex interrupt ID value xor al,al ; AL = 00H int 2Fh ; multiplex interrupt test al,al jz L103 ; jump if ok to install cmp al,0FFh jne L102 ; jump if not already installed mov al,2 call FatalError ; already installed L102: mov al,3 call FatalError ; can't install ; Get addresses of InDOS and ErrorMode flags L103: call GetDOSFlags ; Install this TSR's interrupt handlers push es ; preserve PSP segment mov cx,NISR mov si,offset StartISRList L104: lodsb ; AL = interrupt number ; DS:SI -> byte past interrupt number push ax ; preserve AX mov ah,35h ; INT 21H function 35H int 21h ; ES:BX = previous interrupt vector mov [si+1],bx ; save offset and segment .. mov [si+3],es ; .. of previous handler pop ax ; AL = interrupt number push ds ; preserve DS mov dx,[si+5] mov bx,seg RESIDENT_GROUP mov ds,bx ; DS:DX -> this TSR's handler mov ah,25h ; INT 21H function 25H int 21h ; (set interrupt vector) pop ds ; restore DS add si,7 ; DS:SI -> next in list loop L104 ; Free the environment pop es ; ES = PSP segment push es ; preserve PSP segment mov es,es:[2Ch] ; ES = segment of environment mov ah,49h ; INT 21H function 49H int 21h ; (free memory block) ; Terminate and stay resident pop ax ; AX = PSP segment mov dx,cs ; DX = paragraph address of start of ; transient portion (end of resident ; portion) sub dx,ax ; DX = size of resident portion mov ax,3100h ; AH = INT 21H function number ; AL = 00H (return code) int 21h InstallSnapTSR ENDP GetDOSVersion PROC near ; Caller: DS = seg RESIDENT_DATA ; ES = PSP ; Returns: AH = major version ; AL = minor version ASSUME ds:RESIDENT_DATA mov ax,30h ; INT 21h function 30H: ; (get MS-DOS version) int 21h cmp al,2 jb L110 ; jump if version 1.x xchg ah,al ; AH = major version ; AL = minor version mov DOSVersion,ax ; save with major version in ; high-order byte ret L110: mov al,00h call FatalError ; abort if version 1.x GetDOSVersion ENDP GetDOSFlags PROC near ; Caller: DS = seg RESIDENT_DATA ; Returns: InDOSAddr -> InDOS ; ErrorModeAddr -> ErrorMode ; Destroys: AX,BX,CX,DI ASSUME ds:RESIDENT_DATA ; Get InDOS address from MS-DOS push es mov ah,34h ; INT 21H function number int 21h ; ES:BX -> InDOS mov word ptr InDOSAddr,bx mov word ptr InDOSAddr+2,es ; Determine ErrorMode address mov word ptr ErrorModeAddr+2,es ; assume ErrorMode is ; in the same segment ; as InDOS mov ax,DOSVersion cmp ax,30Ah jb L120 ; jump if MS-DOS version earlier ; than 3.1 .. cmp ax,0A00h jae L120 ; .. or MS OS/2-DOS 3.x box dec bx ; in MS-DOS 3.1 and later, ErrorMode mov word ptr ErrorModeAddr,bx ; is just before InDOS jmp short L125 L120: ; scan MS-DOS segment for ErrorMode mov cx,0FFFFh ; CX = maximum number of bytes to scan xor di,di ; ES:DI -> start of MS-DOS segment L121: mov ax,word ptr cs:LF2 ; AX = opcode for INT 28H L122: repne scasb ; scan for first byte of fragment jne L126 ; jump if not found cmp ah,es:[di] ; inspect second byte of opcode jne L122 ; jump if not INT 28H mov ax,word ptr cs:LF1 + 1 ; AX = opcode for CMP cmp ax,es:[di][LF1-LF2] jne L123 ; jump if opcode not CMP mov ax,es:[di][(LF1-LF2)+2] ; AX = offset of ErrorMode jmp short L124 ; in DOS segment L123: mov ax,word ptr cs:LF3 + 1 ; AX = opcode for TEST cmp ax,es:[di][LF3-LF4] jne L121 ; jump if opcode not TEST mov ax,es:[di][(LF3-LF4)+2] ; AX = offset of ErrorMode L124: mov word ptr ErrorModeAddr,ax L125: pop es ret ; Come here if address of ErrorMode not found L126: mov al,04H call FatalError ; Code fragments for scanning for ErrorMode flag LFnear LABEL near ; dummy labels for addressing LFbyte LABEL byte LFword LABEL word ; MS-DOS versions earlier than 3.1 LF1: cmp ss:LFbyte,0 ; CMP ErrorMode,0 jne LFnear LF2: int 28h ; MS-DOS versions 3.1 and later LF3: test ss:LFbyte,0FFh ; TEST ErrorMode,0FFH jne LFnear push ss:LFword LF4: int 28h GetDOSFlags ENDP FatalError PROC near ; Caller: AL = message number ; ES = PSP ASSUME ds:TRANSIENT_DATA push ax ; save message number on stack mov bx,seg TRANSIENT_DATA mov ds,bx ; Display the requested message mov bx,offset MessageTable xor ah,ah ; AX = message number shl ax,1 ; AX = offset into MessageTable add bx,ax ; DS:BX -> address of message mov dx,[bx] ; DS:BX -> message mov ah,09h ; INT 21H function 09H (display string) int 21h ; display error message pop ax ; AL = message number or al,al jz L130 ; jump if message number is zero ; (MS-DOS versions 1.x) ; Terminate (MS-DOS 2.x and later) mov ah,4Ch ; INT 21H function 4CH int 21h ; (terminate process with return code) ; Terminate (MS-DOS 1.x) L130 PROC far push es ; push PSP:0000H xor ax,ax push ax ret ; far return (jump to PSP:0000H) L130 ENDP FatalError ENDP TRANSIENT_TEXT ENDS PAGE ; ; ; Transient data segment ; ; TRANSIENT_DATA SEGMENT word public 'DATA' MessageTable DW Message0 ; MS-DOS version error DW Message1 ; PRINT.COM found in MS-DOS 2.x DW Message2 ; already installed DW Message3 ; can't install DW Message4 ; can't find flag Message0 DB CR,LF,'TSR requires MS-DOS 2.0 or later version',CR,LF,'$' Message1 DB CR,LF,'Can''t install TSR: PRINT.COM active',CR,LF,'$' Message2 DB CR,LF,'This TSR is already installed',CR,LF,'$' Message3 DB CR,LF,'Can''t install this TSR',CR,LF,'$' Message4 DB CR,LF,'Unable to locate MS-DOS ErrorMode flag',CR,LF,'$' TRANSIENT_DATA ENDS END InstallSnapTSR