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undos.asm
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Assembly Source File
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1983-10-23
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8KB
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187 lines
TITLE UNDOS ;UN-DOS A SYSTEM DISK
PAGE 25,80 ;25 LINES PER PAGE, 80 COLUMNS PER LINE
CODE SEGMENT BYTE PUBLIC 'CODE'
ASSUME CS:CODE,DS:CODE
EXTFCB STRUC
FLAG DB 0FFH ;EXTENDED FCB FLAG BYTE
RES1 DB 5 DUP (0) ;RESERVED FOR SYSTEM USE
ATTR DB 06H ;ATTRIBUTE BYTE (HIDDEN, SYSTEM)
DRV DB 0 ;DRIVE NUMBER
FILE DB " " ;FILE NAME
EXT DB " " ;FILE EXTENSION
BLK DW 0 ;CURRENT BLOCK NUMBER
REC DW 0 ;LOGICAL RECORD SIZE OF FILE
SIZE1 DW 0 ;LSB OF FILE SIZE
SIZE2 DW 0 ;MSB OF FILE SIZE
DATE DW 0 ;DATE FILE WAS CREATED
TIME DW 0 ;TIME THE FILE WAS CREATED
RES2 DB 8 DUP (0) ;RESERVED FOR SYSTEM USE
RELREC DB 0 ;CURRENT RELATIVE RECORD NUMBER (IN BLOCK)
RREC1 DW 0 ;LSB OF RELATIVE RECORD NUMBER
RREC2 DW 0 ;MSB OF RELATIVE RECORD NUMBER
SAVE1 DW 0 ;SAVE AREA ONE
SAVE2 DW 0 ;SAVE AREA TWO
SAVE3 DW 0 ;SAVE AREA THREE
EXTFCB ENDS ;END OF EXTFCB STRUCTURE
INPUT EQU 0C08H ;CLEAR KEYBOARD BUFFER THEN INPUT CODE
PRINT EQU 09H ;PRINT STRING FUNCTION CODE
OPEN EQU 0FH ;OPEN FILE FUNCTION CODE
CLOSE EQU 10H ;CLOSE FILE FUNCTION CODE
GETDRV EQU 19H ;GET CURRENT DEFAULT DRIVE FUNCTION CODE
SETDTA EQU 1AH ;SET DISK TRANSFER ADDRESS FUNCTION CODE
TABLE EQU 1CH ;GET ALLOCATION TABLE ADDRESS FUNCTION CODE
RBLKRD EQU 27H ;RANDOM BLOCK READ FUNCTION CODE
RBLKWR EQU 28H ;RANDOM BLOCK WRITE FUNCTION CODE
DSPEC EQU BYTE PTR 5CH ;POINTER TO DRIVE SPECIFICATION
PARAM EQU BYTE PTR 5DH ;POINTER TO INPUT PARAMETER
BAD EQU 0FFH ;ERROR CODE
CONV EQU 40H ;BINARY TO ASCII CONVERSION FACTOR
ZERO EQU 00H ;ZERO BYTE
ONE EQU 01H ;ONE WORD
BLANK EQU 20H ;ASCII BLANK
CRLF EQU 0A0DH ;ASCII LINE FEED, CARRIAGE RETURN
BIOMAX EQU 8000H ;MAXIMUM BYTE COUNT FOR IBMBIO FILE
DOSMAX EQU 2000H ;MAXIMUM BYTE COUNT FOR IBMDOS FILE
EXIT MACRO ;TERMINATE INTERRUPT MACRO
INT 20H ;DO THE TERMINATE INTERRUPT 20
ENDM ;END OF THE EXIT MACRO
DOS MACRO ;DOS INTERRUPT CALL MACRO
INT 21H ;DO THE DOS INTERRUPT 21
ENDM ;END OF DOS MACRO
ORG 100H ;ORIGIN ADDRESS FOR COM FILES
UNDOS PROC NEAR ;ENTRY POINT FROM DOS 1.1
JMP SHORT START ;GO TO THE START-UP POINT
ILLEGAL LABEL NEAR ;ILLEGAL PARAMETER CODE SECTION
MOV DX,OFFSET MSG2 ;POINT TO ILLEGAL PARAMETER MESSAGE
JMP MSGRET ;GO PRINT THE MESSAGE AND RETURN TO DOS
INVALID LABEL NEAR ;INVALID DRIVE CODE SECTION
MOV DX,OFFSET MSG1 ;POINT TO INVALID DRIVE MESSAGE
JMP MSGRET ;GO PRINT THE MESSAGE AND RETURN TO DOS
INSERT LABEL NEAR ;INSERT CORRECT DISK SECTION
MOV AL,[DEFAULT] ;GET CURRENT DEFAULT DRIVE NUMBER
ADD AL,CONV ;CONVERT DRIVE NUMBER TO ASCII
MOV [DRIVE],AL ;STUFF DRIVE NUMBER IN MESSAGE
MOV DX,OFFSET MSG3 ;POINT TO INSERT SYSTEM DISK MESSAGE
MOV AH,PRINT ;GET PRINT STRING FUNCTION CODE
DOS ;PRINT THE MESSAGE
MOV AX,INPUT ;LOAD AX WITH CLEAR BUFFER AND INPUT CODE
DOS ;GO WAIT FOR ANY CHARACTER
XOR AL,AL ;ZERO THE AL REGISTER
START LABEL NEAR ;INITIAL STARTING CODE (FROM ENTRY POINT)
CMP [DS:PARAM],BLANK;CHECK FOR ENTERED FILENAME OR PARAMETER
JNZ ILLEGAL ;JUMP IF FILENAME OR PARAMETER ENTERED
CMP AL,BAD ;CHECK FOR INVALID DRIVE SPECIFICATION
JZ INVALID ;JUMP IF INVALID DRIVE SPECIFIED
MOV AL,[DS:DSPEC] ;GET THE REQUESTED DRIVE NUMBER
MOV [IBMDOS].DRV,AL ;PUT DRIVE NUMBER IN IBMDOS.COM FCB
MOV [IBMBIO].DRV,AL ;PUT DRIVE NUMBER IN IBMBIO.COM FCB
MOV AH,OPEN ;LOAD AH WITH OPEN FILE FUNCTION CODE
MOV DX,OFFSET IBMBIO;POINT TO FCB FOR IBMBIO.COM FILE
DOS ;ATTEMPT TO OPEN THE FILE IBMBIO.COM
OR AL,AL ;CHECK TO SEE IF FILE IS PRESENT
JNZ INSERT ;JUMP IF THIS IS NOT A GOOD DISK
MOV DX,OFFSET IBMDOS;POINT TO FCB FOR IBMDOS.COM FILE
MOV AH,OPEN ;LOAD AH WITH OPEN FILE FUNCTION CODE
DOS ;ATTEMPT TO OPEN THE FILE IBMDOS.COM
OR AL,AL ;CHECK TO SEE IF FILE IS PRESENT
JNZ INSERT ;JUMP IF THIS IS NOT A GOOD DISK
MOV AH,SETDTA ;LOAD AH WITH SET DTA FUNCTION CODE
MOV DX,OFFSET DTA2 ;POINT TO DISK TRANSFER ADDRESS FOR IBMBIO.COM
DOS ;SET THE DISK TRANSFER ADDRESS
MOV AX,ONE ;LOAD AX WITH ONE
MOV [IBMBIO].REC,AX ;SET IBMBIO.COM RECORD SIZE TO ONE
MOV [IBMDOS].REC,AX ;SET IBMDOS.COM RECORD SIZE TO ONE
MOV BX,OFFSET IBMBIO;POINT TO FCB FOR IBMBIO.COM
MOV CX,BIOMAX ;LOAD CX WITH MAXIMUM RECORD COUNT (BYTES)
CALL READ ;CALL ROUTINE TO READ IN THE FILE
MOV BX,OFFSET IBMBIO;POINT TO FCB FOR IBMBIO.COM
MOV DX,OFFSET DTA2 ;POINT TO WHERE READ IN
CALL WIPE ;CALL ROUTINE TO WIPE-OUT THE CODE
MOV DX,OFFSET DTA1 ;POINT TO DISK TRANSFER ADDRESS FOR IBMDOS.COM
MOV AH,SETDTA ;LOAD AH WITH SET DTA FUNCTION CODE
DOS ;SET THE DISK TRANSFER ADDRESS
MOV BX,OFFSET IBMDOS;POINT TO FCB FOR IBMDOS.COM
MOV CX,DOSMAX ;LOAD CX WITH MAXIMUM RECORD COUNT (BYTES)
CALL READ ;CALL ROUTINE TO READ THE FILE
MOV BX,OFFSET IBMDOS;POINT TO FCB FOR IBMDOS.COM
MOV DX,OFFSET DTA1 ;POINT TO WHERE IT WAS READ IN
CALL WIPE ;CALL ROUTINE TO WIPE-OUT THE CODE
MOV DX,OFFSET DTA2 ;POINT TO DISK TRANSFER AREA FOR IBMBIO.COM
MOV AH,SETDTA ;LOAD AH WITH SET DTA FUNCTION CODE
DOS ;SET THE DISK TRANSFER ADDRESS
MOV BX,OFFSET IBMBIO;POINT TO IBMBIO.COM FCB
CALL WRITE ;CALL ROUTINE TO WRITE THE FILE
MOV DX,OFFSET DTA1 ;POINT TO DISK TRANSFER AREA FOR IBMDOS.COM
MOV AH,SETDTA ;LOAD AH WITH SET DTA FUNCTION CODE
DOS ;SET THE DISK TRANSFER ADDRESS
MOV BX,OFFSET IBMDOS;POINT TO IBMDOS.COM FCB
CALL WRITE ;CALL ROUTINE TO WRITE THE FILE
MOV DX,OFFSET MSG4 ;POINT TO SYSTEM ERASED MESSAGE
MSGRET LABEL NEAR ;PRINT MESSAGE AND RETURN TO DOS SECTION
MOV AH,PRINT ;LOAD AH WITH PRINT STRING FUNCTION CODE
DOS ;PRINT THE MESSAGE
EXIT ;RETURN CONTROL TO PC-DOS
UNDOS ENDP ;END OF SYS PROCEDURE
WIPE PROC NEAR ;PROCEDURE TO WIPE-OUT DISK TRANSFER AREA
MOV CX,[BX].SAVE3 ;GET THE NUMBER OF BYTES TO WIPE-OUT
MOV DI,DX ;GET OFFSET TO DISK TRANSFER AREA
PUSH DS ;SAVE A COPY OF DS ON THE STACK
POP ES ;PUT THE DS COPY INTO ES (POINT ES:DI TO DTA)
XOR AL,AL ;ZERO THE AL REGISTER
REPZ STOSB ;ZERO THE DISK TRANSFER AREA
RET ;RETURN TO THE CALLER
WIPE ENDP ;END OF THE WIPE PROCEDURE
READ PROC NEAR ;ROUTINE TO READ A FILE
MOV AH,RBLKRD ;LOAD AH WITH RANDOM BLOCK READ CODE
MOV DX,BX ;POINT DX TO FCB
DOS ;READ THE BLOCK
MOV [BX].SAVE3,CX ;SAVE THE FILE SIZE (BYTES)
MOV AX,[BX].DATE ;GET DATE CREATED
MOV [BX].SAVE1,AX ;SAVE DATE CREATED
MOV AX,[BX].TIME ;GET TIME CREATED
MOV [BX].SAVE2,AX ;SAVE TIME CREATED
RET ;RETURN TO THE CALLER
READ ENDP ;END OR READ PROCEDURE
WRITE PROC NEAR ;ROUTINE TO WRITE THE FILE
MOV DX,BX ;MOVE FCB POINTER TO DX
XOR AX,AX ;ZERO AX REGISTER
MOV [BX].RREC1,AX ;SET LSB OF RELATIVE RECORD NUMBER TO ZERO
MOV [BX].RREC2,AX ;SET MSB OF RELATIVE RECORD NUMBER TO ZERO
INC AX ;INCREMENT AX TO ONE
MOV [BX].REC,AX ;SET RELATIVE RECORD SIZE TO ONE (BYTE)
MOV AH,RBLKWR ;LOAD AH WITH RANDOM BLOCK WRITE CODE
MOV CX,[BX].SAVE3 ;GET RECORD COUNT (FILE SIZE IN BYTES)
DOS ;WRITE THE FILE
MOV AX,[BX].SAVE1 ;GET SAVED DATE CREATED (ORIGINAL)
MOV [BX].DATE,AX ;SAVE AS CURRENT DATE
MOV AX,[BX].SAVE2 ;GET SAVED TIME CREATED (ORIGINAL)
MOV [BX].TIME,AX ;SAVE AS CURRENT TIME
MOV AH,CLOSE ;LOAD AH WITH CLOSE FILE CODE
DOS ;CLOSE THE FILE
RET ;RETURN TO THE CALLER
WRITE ENDP ;END OF WRITE PROCEDURE
MSG1 EQU THIS WORD ;MESSAGE NUMBER ONE
DB "Invalid drive specification$"
MSG2 EQU THIS WORD ;MESSAGE NUMBER TWO
DB "Invalid parameter$"
MSG3 EQU THIS WORD ;MESSAGE NUMBER THREE
DB "Insert system disk in drive "
DRIVE EQU THIS BYTE ;DRIVE NUMBER IN PRINT MESSAGE
DB "A"
DW CRLF
DB "and strike any key when ready"
DW CRLF
DB "$"
MSG4 EQU THIS WORD ;MESSAGE NUMBER SIX
DB "System erased!$"
DEFAULT EQU THIS BYTE ;SAVE AREA FOR CURRENT DEFAULT DRIVE NUMBER
DB 0
IBMBIO EXTFCB <,,,,"IBMBIO","COM">
IBMDOS EXTFCB <,,,,"IBMDOS","COM">
CHK EQU THIS WORD/2*2
OFF EQU THIS WORD-CHK
DTA1 EQU THIS WORD+1 ;DISK TRANSFER AREA ONE (FILE IBMDOS)
DTA2 EQU DTA1+DOSMAX ;DISK TRANSFER AREA TWO (FILE IBMBIO)
CODE ENDS ;END OF CODE SEGMENT
END UNDOS ;END OF UNDOS COMMAND