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Assembly Source File | 1985-03-18 | 69.9 KB | 2,074 lines

PAGE ,132 TITLE VDISK - Virtual Disk Device Driver, Version 1.0 ;VDISK simulates a disk drive, using Random Access Memory as the storage medium. ;(C) Copyright IBM Corporation, 1984 ;Licensed Material - Program Property of IBM ;Author: Dick Dievendorff ;Add the following statement to CONFIG.SYS ; DEVICE=[d:][path]VDISK.SYS bbb sss ddd [/E] ; where: bbb is the desired buffer size (in kilobytes) ; minimum 1KB, maximum is size of available memory, ; default is 64KB. ; VDISK will leave at least 64KB of available memory, ; although subsequent device drivers (other than VDISK) ; other programs that make themselves resident, and ; COMMAND.COM will result in less than 64KB as shown ; by CHKDSK. ; Must be large enough for 1 boot sector + FAT sectors ; + 1 directory sector + at least 1 data cluster, ; or the device driver won't be installed. ; sss is the desired sector size (in bytes) ; 128, 256, or 512, default is 128. ; Will be adjusted if number of FAT entries > 0FE0H ; ddd is the desired number of directory entries ; Minimum 2, maximum 512, default 64. ; Will be rounded upward to sector size boundary. ; /E may only be used if extended memory above 1 megabyte ; is to be used. INT 15H functions 87H and 88H are used ; to read and write this extended memory. ; Brackets indicate optional operands. ; Samples: ; DEVICE=\path\VDISK.SYS 160 512 64 ; results in a 160KB VDISK, with 512 byte sectors, 64 directory entries ; DEVICE=VDISK.SYS Buffersize 60 Sectorsize 128 Directory entries 32 ; (since only numbers are interpreted, you may comment the line with ; non-numeric characters) ;Message text for VDISK is in module VDISKMSG. SUBTTL Structure Definitions PAGE ;-----------------------------------------------------------------------; ; Request Header (Common portion) ; ;-----------------------------------------------------------------------; RH EQU DS:[BX] ;addressability to Request Header structure RHC STRUC ;fields common to all request types DB ? ;length of Request Header (including data) DB ? ;unit code (subunit) RHC_CMD DB ? ;command code RHC_STA DW ? ;status DQ ? ;reserved for DOS RHC ENDS ;end of common portion CMD_INPUT EQU 4 ;RHC_CMD is INPUT request ;status values for RHC_STA STAT_DONE EQU 01H ;function complete status (high order byte) STAT_CMDERR EQU 8003H ;invalid command code error STAT_CRC EQU 8004H ;CRC error STAT_SNF EQU 8008H ;sector not found error STAT_BUSY EQU 0200H ;busy bit (9) for Removable Media call ;-----------------------------------------------------------------------; ; Request Header for INIT command ; ;-----------------------------------------------------------------------; RH0 STRUC DB (TYPE RHC) DUP (?) ;common portion RH0_NUN DB ? ;number of units ;set to 1 if installation succeeds, ;set to 0 to cause installation failure RH0_ENDO DW ? ;offset of ending address RH0_ENDS DW ? ;segment of ending address RH0_BPBO DW ? ;offset of BPB array address RH0_BPBS DW ? ;segment of BPB array address RH0_DRIV DB ? ;drive code (DOS 3 only) RH0 ENDS RH0_BPBA EQU DWORD PTR RH0_BPBO ;offset/segment of BPB array address ;Note: RH0_BPBA at entry to INIT points to all after DEVICE= on CONFIG.SYS stmt ;-----------------------------------------------------------------------; ; Request Header for MEDIA CHECK Command ; ;-----------------------------------------------------------------------; RH1 STRUC DB (TYPE RHC) DUP (?) ;common portion DB ? ;media descriptor RH1_RET DB ? ;return information RH1 ENDS ;-----------------------------------------------------------------------; ; Request Header for BUILD BPB Command ; ;-----------------------------------------------------------------------; RH2 STRUC DB (TYPE RHC) DUP(?) ;common portion DB ? ;media descriptor DW ? ;offset of transfer address DW ? ;segment of transfer address RH2_BPBO DW ? ;offset of BPB table address RH2_BPBS DW ? ;segment of BPB table address RH2 ENDS ;-----------------------------------------------------------------------; ; Request Header for INPUT, OUTPUT, and OUTPUT with verify ; ;-----------------------------------------------------------------------; RH4 STRUC DB (TYPE RHC) DUP (?) ;common portion DB ? ;media descriptor RH4_DTAO DW ? ;offset of transfer address RH4_DTAS DW ? ;segment of transfer address RH4_CNT DW ? ;sector count RH4_SSN DW ? ;starting sector number RH4 ENDS RH4_DTAA EQU DWORD PTR RH4_DTAO ;offset/segment of transfer address ;-----------------------------------------------------------------------; ; Segment Descriptor (part of Global Descriptor Table) ; ;-----------------------------------------------------------------------; DESC STRUC ;data segment descriptor DESC_LMT DW 0 ;segment limit (length) DESC_BASEL DW 0 ;bits 15-0 of physical address DESC_BASEH DB 0 ;bits 23-16 of physical address DB 0 ;access rights byte DW 0 ;reserved DESC ENDS SUBTTL Equates and Macro Definitions PAGE MEM_SIZE EQU 12H ;BIOS memory size determination INT ;returns system size in KB in AX EM_INT EQU 15H ;extended memory BIOS interrupt INT EM_BLKMOVE EQU 87H ;block move function EM_MEMSIZE EQU 88H ;memory size determination in KB BOOT_INT EQU 19H ;bootstrap DOS DOS EQU 21H ;DOS request INT DOS_PCHR EQU 02H ;print character function DOS_PSTR EQU 09H ;print string function DOS_VERS EQU 30H ;get DOS version TAB EQU 09H ;ASCII tab LF EQU 0AH ;ASCII line feed CR EQU 0DH ;ASCII carriage return PARA_SIZE EQU 16 ;number of bytes in one 8088 paragraph DIR_ENTRY_SIZE EQU 32 ;number of bytes per directory entry MAX_FATE EQU 0FE0H ;largest number of FAT entries allowed ;default values used if parameters are omitted DFLT_BSIZE EQU 64 ;default VDISK buffer size (KB) DFLT_SSZ EQU 128 ;default sector size DFLT_DIRN EQU 64 ;default number of directory entries MIN_DIRN EQU 2 ;minimum number of directory entries MAX_DIRN EQU 512 ;maximum number of directory entries STACK_SIZE EQU 512 ;length of stack during initialization ;-----------------------------------------------------------------------; ; MSG invokes the console message subroutine ; ;-----------------------------------------------------------------------; MSG MACRO TEXT PUSH DX ;;save DX across call MOV DX,OFFSET TEXT ;;point to message CALL SHOW_MSG ;;issue message POP DX ENDM SUBTTL Resident Data Area PAGE ;-----------------------------------------------------------------------; ; Map INT 19H vector in low storage ; ;-----------------------------------------------------------------------; INT_VEC SEGMENT AT 00H ORG 4*BOOT_INT BOOT_VEC LABEL DWORD BOOT_VECO DW ? ;offset BOOT_VECS DW ? ;segment INT_VEC ENDS CSEG SEGMENT PARA PUBLIC 'CODE' ASSUME CS:CSEG ;-----------------------------------------------------------------------; ; Resident data area. ; ; ; ; All variables and constants required after initialization ; ; part one are defined here. ; ;-----------------------------------------------------------------------; START EQU $ ;begin resident VDISK data & code ;DEVICE HEADER - must be at offset zero within device driver DD -1 ;becomes pointer to next device header DW 0800H ;attribute (IBM format block device) ;supports OPEN/CLOSE/RM calls DW OFFSET STRATEGY ;pointer to device "strategy" routine DW OFFSET IRPT ;pointer to device "interrupt handler" DB 1 ;number of block devices DB 7 DUP (?) ;7 byte filler (remainder of 8-byte name) ;END OF DEVICE HEADER ;This volume label is placed into the directory of the new VDISK ;This constant is also used to determine if a previous extended memory VDISK ;has been installed. VOL_LABEL DB 'VDISK V1.0' ;00-10 volume name (shows program level) DB 08H ;11-11 attribute (volume label) DT 0 ;12-21 reserved DW 6000H ;22-23 time=12:00 noon DW 08E3H ;24-25 date=07/03/84 VOL_LABEL_LEN EQU $-VOL_LABEL ;length of volume label ;The following field, in the first extended memory VDISK device driver, ;is the 24-bit address of the first free byte of extended memory. ;This address is not in the common offset/segment format. ;The initial value, 10 0000H, is 1 megabyte. AVAIL_LO DW 0 ;address of first free byte of AVAIL_HI DB 10H ;extended memory ;The INT 19H vector is "stolen" by the first VDISK installed in extended memory. ;The original content of the interrupt vector is saved here. INTV19 LABEL DWORD INTV19O DW ? ;offset INTV19S DW ? ;segment PARAS_PER_SECTOR DW ? ;number of 16-byte paragraphs in one sector START_BUFFER_PARA DW ? ;segment address of start of VDISK buffer ;for extended memory, this segment address ;is the end of the VDISK device driver. EM_SW DB 0 ;non-zero if Extended Memory EM_STAT DW 0 ;AX from last unsuccessful extended memory I/O START_EM_LO DW ? ;24-bit address of start of VDISK buffer START_EM_HI DB ? ;(extended memory only) WPARA_SIZE DW PARA_SIZE ;number of bytes in one paragraph MAX_CNT DW ? ;(0FFFFH/BPB_SSZ) truncated, the maximum ;number of sectors that can be transferred ;without worrying about 64KB wrap SECT_LEFT DW ? ;sectors left to transfer IO_SRCA LABEL DWORD ;offset/segment of source IO_SRCO DW ? ;offset IO_SRCS DW ? ;segment IO_TGTA LABEL DWORD ;offset/segment of target IO_TGTO DW ? ;offset IO_TGTS DW ? ;segment ;-----------------------------------------------------------------------; ; BIOS Parameter Block (BPB) ; ;-----------------------------------------------------------------------; ;This is where the characteristics of the virtual disk are established. ;A copy of this block is moved into the boot record of the virtual disk. ;DEBUG can be used to read sector zero of the virtual disk to examine the ;boot record copy of this block. BPB LABEL BYTE ;BIOS Parameter Block (BPB) BPB_SSZ DW 0 ;number of bytes per disk sector BPB_AUSZ DB 1 ;sectors per allocation unit BPB_RES DW 1 ;number of reserved sectors (for boot record) BPB_FATN DB 1 ;number of File Allocation Table (FAT) copies BPB_DIRN DW 0 ;number of root directory entries BPB_SECN DW 1 ;total number of sectors ;computed from buffer size and sector size ;(this includes reserved, FAT, directory, ;and data sectors) BPB_MCB DB 0FEH ;media descriptor byte BPB_FATSZ DW 1 ;number of sectors occupied by a single FAT ;computed from BPBSSZ and BPBSECN BPB_LEN EQU $-BPB ;length of BIOS parameter block BPB_PTR DW BPB ;BIOS Parameter Block pointer array (1 entry) ;-----------------------------------------------------------------------; ; Request Header (RH) address, saved here by "strategy" routine ; ;-----------------------------------------------------------------------; RH_PTRA LABEL DWORD RH_PTRO DW ? ;offset RH_PTRS DW ? ;segment ;-----------------------------------------------------------------------; ; Global Descriptor Table (GDT), used for extended memory moves ; ;-----------------------------------------------------------------------; ;Access Rights Byte (93H) is ; P=1 (segment is mapped into physical memory) ; E=0 (data segment descriptor) ; D=0 (grow up segment, offsets must be <= limit) ; W=1 (data segment may be written into) ; DPL=0 (privilege level 0) GDT LABEL BYTE ;begin global descriptor table DESC <> ;dummy descriptor DESC <> ;descriptor for GDT itself SRC DESC <,,,93H,> ;source descriptor TGT DESC <,,,93H,> ;target descriptor DESC <> ;BIOS CS descriptor DESC <> ;stack segment descriptor SUBTTL INT 19H (boot) interrupt handler PAGE ;-----------------------------------------------------------------------; ; INT 19H Interrupt Handler routine ; ;-----------------------------------------------------------------------; ;The INT 19H vector is altered by VDISK initialization to point to this ;routine within the first extended memory VDISK device driver. ;The vector points to the device driver so that subsequent VDISKs installed ;in extended memory can find the first one to determine what memory has ;already been allocated to VDISKs. ;This routine restores the original INT 19H vector's content, then jumps ;to the original routine. ;INT 19H, the "Boot" INT, is always altered when DOS is booted. ;This routine is entered with interrupts disabled. VDISK_INT19 PROC ;INT 19H received PUSH DS ;save registers we're going to alter PUSH AX XOR AX,AX MOV DS,AX ;set DS = 0 ASSUME DS:INT_VEC MOV AX,CS:INTV19O ;get offset of saved vector MOV DS:BOOT_VECO,AX ;store offset in interrupt vector MOV AX,CS:INTV19S ;get segment of saved vector MOV DS:BOOT_VECS,AX ;store segment in interrupt vector POP AX POP DS JMP CS:INTV19 ;go to original interrupt routine VDISK_INT19 ENDP ASSUME DS:NOTHING SUBTTL Device Strategy & interrupt entry points PAGE ;-----------------------------------------------------------------------; ; Device "strategy" entry point ; ; ; ; Retain the Request Header address for use by Interrupt routine ; ;-----------------------------------------------------------------------; STRATEGY PROC FAR MOV CS:RH_PTRO,BX ;offset MOV CS:RH_PTRS,ES ;segment RET STRATEGY ENDP ;-----------------------------------------------------------------------; ; Table of command processing routine entry points ; ;-----------------------------------------------------------------------; CMD_TABLE LABEL WORD DW OFFSET INIT_P1 ; 0 - Initialization DW OFFSET MEDIA_CHECK ; 1 - Media check DW OFFSET BLD_BPB ; 2 - Build BPB DW OFFSET INPUT_IOCTL ; 3 - IOCTL input DW OFFSET INPUT ; 4 - Input DW OFFSET INPUT_NOWAIT ; 5 - Non destructive input no wait DW OFFSET INPUT_STATUS ; 6 - Input status DW OFFSET INPUT_FLUSH ; 7 - Input flush DW OFFSET OUTPUT ; 8 - Output DW OFFSET OUTPUT_VERIFY ; 9 - Output with verify DW OFFSET OUTPUT_STATUS ;10 - Output status DW OFFSET OUTPUT_FLUSH ;11 - Output flush DW OFFSET OUTPUT_IOCTL ;12 - IOCTL output DW OFFSET DEVICE_OPEN ;13 - Device OPEN DW OFFSET DEVICE_CLOSE ;14 - Device CLOSE MAX_CMD EQU ($-CMD_TABLE)/2 ;highest valid command follows DW OFFSET REMOVABLE_MEDIA ;15 - Removable media ;-----------------------------------------------------------------------; ; Device "interrupt" entry point ; ;-----------------------------------------------------------------------; IRPT PROC FAR ;device interrupt entry point PUSH DS ;save all registers modified PUSH ES PUSH AX PUSH BX PUSH CX PUSH DX PUSH DI PUSH SI ;BP isn't used, so it isn't saved CLD ;all moves forward LDS BX,CS:RH_PTRA ;get RH address passed to "strategy" into DS:BX MOV AL,RH.RHC_CMD ;command code from Request Header CBW ;zero AH (if AL > 7FH, next compare will ;catch that error) CMP AL,MAX_CMD ;if command code is too high JA IRPT_CMD_HIGH ;jump to error routine MOV DI,OFFSET IRPT_CMD_EXIT ;return addr from command processor PUSH DI ;push return address onto stack ;command routine issues "RET" ADD AX,AX ;double command code for table offset MOV DI,AX ;put into index register for JMP XOR AX,AX ;initialize return to "no error" ;At entry to command processing routine: ; DS:BX = Request Header address ; CS = VDISK code segment address ; AX = 0 ; top of stack is return address, IRPT_CMD_EXIT JMP CS:CMD_TABLE[DI] ;call routine to handle the command IRPT_CMD_ERROR: ;CALLed for unsupported character mode commands INPUT_IOCTL: ;IOCTL input INPUT_NOWAIT: ;Non-destructive input no wait INPUT_STATUS: ;Input status INPUT_FLUSH: ;Input flush OUTPUT_IOCTL: ;IOCTL output OUTPUT_STATUS: ;Output status OUTPUT_FLUSH: ;Output flush POP AX ;pop return address off stack IRPT_CMD_HIGH: ;JMPed to if RHC_CMD > MAX_CMD MOV AX,STAT_CMDERR ;"invalid command" and error IRPT_CMD_EXIT: ;return from command routine ;AX = value to OR into status word LDS BX,CS:RH_PTRA ;restore DS:BX as Request Header pointer OR AH,STAT_DONE ;add "done" bit to status word MOV RH.RHC_STA,AX ;store status into request header POP SI ;restore registers POP DI POP DX POP CX POP BX POP AX POP ES POP DS RET IRPT ENDP SUBTTL Command Processing routines PAGE ;-----------------------------------------------------------------------; ; Command Code 1 - Media Check ; ; At entry, DS:BX point to request header, AX = 0 ; ;-----------------------------------------------------------------------; MEDIA_CHECK PROC MOV RH.RH1_RET,1 ;indicate media not changed RET ;AX = zero, no error MEDIA_CHECK ENDP ;-----------------------------------------------------------------------; ; Command Code 2 - Build BPB ; ; At entry, DS:BX point to request header, AX = 0 ; ;-----------------------------------------------------------------------; BLD_BPB PROC MOV RH.RH2_BPBO,OFFSET BPB ;return pointer to our BPB MOV RH.RH2_BPBS,CS RET ;AX = zero, no error BLD_BPB ENDP ;-----------------------------------------------------------------------; ; Command Code 13 - Device Open ; ; Command Code 14 - Device Close ; ; Command Code 15 - Removable media ; ; At entry, DS:BX point to request header, AX = 0 ; ;-----------------------------------------------------------------------; REMOVABLE_MEDIA PROC MOV AX,STAT_BUSY ;set status bit 9 (busy) ;indicating non-removable media DEVICE_OPEN: ;NOP for device open DEVICE_CLOSE: ;NOP for device close RET REMOVABLE_MEDIA ENDP ;fall thru to return ;-----------------------------------------------------------------------; ; Command Code 4 - Input ; ; Command Code 8 - Output ; ; Command Code 9 - Output with verify ; ; At entry, DS:BX point to request header, AX = 0 ; ;-----------------------------------------------------------------------; INOUT PROC INPUT: OUTPUT: OUTPUT_VERIFY: ;Make sure I/O is entirely within the VDISK sector boundaries MOV CX,CS:BPB_SECN ;get total sector count MOV AX,RH.RH4_SSN ;starting sector number CMP AX,CX ;can't exceed total count JA INOUT_E1 ;jump if start > total ADD AX,RH.RH4_CNT ;start + sector count CMP AX,CX ;can't exceed total count JNA INOUT_A ;jump if start + count <= total INOUT_E1: ;I/O not within VDISK sector boundaries MOV RH.RH4_CNT,0 ;set sectors transferred to zero MOV AX,STAT_SNF ;indicate 'Sector not found' error RET ;return with error status in AX INOUT_A: ;I/O within VDISK bounds MOV AX,RH.RH4_CNT ;get sector count MOV CS:SECT_LEFT,AX ;save as sectors left to process CMP CS:EM_SW,0 ;extended memory mode? JNE INOUT_EM ;jump to extended memory I/O code ;Compute offset and segment of VDISK buffer for starting segment in CX:SI MOV AX,RH.RH4_SSN ;starting sector number MUL CS:PARAS_PER_SECTOR ;* length of one sector in paragraphs ADD AX,CS:START_BUFFER_PARA ;+ segment of VDISK buffer sector 0 MOV CX,AX ;segment address to CX XOR SI,SI ;offset is zero ;Compute address of caller's Data Transfer Addr in DX:AX with smallest offset, ;so that there is no possibility of overflowing a 64KB boundary moving MAX_CNT ;sectors. MOV AX,PARA_SIZE ;16 MUL RH.RH4_DTAS ;* segment of caller's DTA in DX,AX ADD AX,RH.RH4_DTAO ;+ offset of caller's DTA ADC DL,0 ;carry in from addition DIV CS:WPARA_SIZE ;AX is segment of caller's DTA ;DX is smallest offset possible ;AX:DX = DTA address ;AX:DX is caller's DTA segment:offset, CX:SI is VDISK buffer segment:offset ;If this is an OUTPUT request, exchange the source and target addresses CMP RH.RHC_CMD,CMD_INPUT ;INPUT operation? JE INOUT_B ;jump if INPUT operation XCHG AX,CX ;swap source and target segment XCHG DX,SI ;swap source and target offset INOUT_B: ;CX:SI is source, AX:DX is target MOV CS:IO_SRCS,CX ;save source segment MOV CS:IO_SRCO,SI ;save source offset MOV CS:IO_TGTS,AX ;save target segment MOV CS:IO_TGTO,DX ;save target offset JMP SHORT INOUT_E ;AX := SECT_LEFT, test for zero INOUT_C: ;SECT_LEFT in AX, non-zero ; Compute number of sectors to transfer in a single move, ; AX = minimum of (SECT_LEFT, MAX_CNT) ; MAX_CNT is the maximum number of sectors that can be moved without ; spanning a 64KB boundary (0FFFFH / Sector size, remainder truncated) MOV CX,CS:MAX_CNT ;MAX sectors with one move CMP AX,CX ;if SECT_LEFT cannot span 64KB boundary JBE INOUT_D ;then move SECT_LEFT sectors MOV AX,CX ;else move MAX_CNT sectors INOUT_D: SUB CS:SECT_LEFT,AX ;reduce number of sectors left to move ;Move AX sectors from source to target MUL CS:BPB_SSZ ;sectors * sector size = byte count ;(cannot overflow into DX) SHR AX,1 ;/2 = word count MOV CX,AX ;word count to CX for REP MOVSW LDS SI,CS:IO_SRCA ;source segment/offset to DS:SI LES DI,CS:IO_TGTA ;target segment/offset to ES:DI REP MOVSW ;move MOV_CNT sectors ;Update source and target paragraph addresses ;AX has number of words moved SHR AX,1 ;words moved / 8 = paragraphs moved SHR AX,1 SHR AX,1 ADD CS:IO_SRCS,AX ;add paragraphs moved to source segment ADD CS:IO_TGTS,AX ;add paragraphs moved to target segment ;Determine if more sectors need to be transferred INOUT_E: ;do while SECT_LEFT <> zero MOV AX,CS:SECT_LEFT ;get sectors left to transfer OR AX,AX ;set flags JNZ INOUT_C ;go back to transfer some sectors RET ;AX = zero, all sectors transferred SUBTTL Extended Memory I/O routine PAGE ;-----------------------------------------------------------------------; ; Extended Memory I/O routine ; ;-----------------------------------------------------------------------; INOUT_EM: ;Extended memory I/O routine ;change to larger stack MOV SI,SS ;save old SS in SI MOV DX,SP ;save old SP in DX CLI ;disable interrupts MOV AX,CS MOV SS,AX ;set SS = CS MOV SP,OFFSET EM_STACK ;point to new stack STI ;enable interrupts PUSH SI ;save old SS at top of new stack PUSH DX ;save old SP on new stack MOV SI,RH.RH4_DTAO ;caller's DTA offset ;Compute 24-bit address of VDISK sector in CX (hi) and SI (low) MOV AX,RH.RH4_SSN ;starting sector number MUL CS:BPB_SSZ ;* sector size = offset within buffer ADD AX,CS:START_EM_LO ;+ base address of this VDISK buffer ADC DL,CS:START_EM_HI MOV CX,DX ;save high byte MOV SI,AX ;save low word ;Compute 24-bit address of caller's DTA in DX (hi) and AX (low) MOV AX,PARA_SIZE ;16 MUL RH.RH4_DTAS ;* segment of caller's DTA ADD AX,RH.RH4_DTAO ;+ offset of caller's DTA ADC DL,0 ;carry in from addition ;Caller's DTA address is in CX,SI, VDISK buffer address is in DX,AX. ;If this is an OUTPUT request, exchange the source and target addresses CMP RH.RHC_CMD,CMD_INPUT ;INPUT operation? JE INOUT_EM_B ;jump if INPUT operation XCHG DX,CX ;swap source and target high byte XCHG AX,SI ;swap source and target low word INOUT_EM_B: ;CX,SI is source, DX,AX is target MOV SRC.DESC_BASEL,SI ;low 16 bits of source address MOV SRC.DESC_BASEH,CL ;high 8 bits of source address MOV TGT.DESC_BASEL,AX ;low 16 bits of target address MOV TGT.DESC_BASEH,DL ;high 8 bits of target address JMP SHORT INOUT_EM_E ;AX := SECT_LEFT, test for zero INOUT_EM_C: ;SECT_LEFT in AX, non-zero ; Compute number of sectors to transfer in a single move, ; AX = minimum of (SECT_LEFT, MAX_CNT) ; MAX_CNT is the maximum number of sectors that can be moved without ; spanning a 64KB boundary (0FFFFH / Sector size, remainder truncated) MOV CX,CS:MAX_CNT ;MAX sectors with one move CMP AX,CX ;if SECT_LEFT cannot span 64KB boundary JBE INOUT_EM_D ;then move SECT_LEFT sectors MOV AX,CX ;else move MAX_CNT sectors INOUT_EM_D: SUB CS:SECT_LEFT,AX ;reduce number of sectors left to move ;Move AX sectors from source to target MUL CS:BPB_SSZ ;sectors * sector size = byte count ;(cannot overflow into DX) MOV TGT.DESC_LMT,AX ;store segment limit (byte count) MOV SRC.DESC_LMT,AX PUSH AX ;preserve byte count on stack SHR AX,1 ;/2 = word count MOV CX,AX ;word count to CX PUSH CS POP ES ;set ES = CS MOV SI,OFFSET GDT ;ES:SI point to GDT MOV AH,EM_BLKMOVE ;function is block move INT EM_INT ;move an even number of words POP CX ;get byte count back from stack OR AH,AH ;get error code JNZ INOUT_EM_XE ;jump if I/O error encountered ;Update source and target addresses ADD SRC.DESC_BASEL,CX ;add bytes moved to source ADC SRC.DESC_BASEH,0 ;pick up any carry ADD TGT.DESC_BASEL,CX ;add bytes moved to target ADC TGT.DESC_BASEH,0 ;pick up any carry ;Determine if more sectors need to be transferred INOUT_EM_E: ;do while SECT_LEFT <> zero MOV AX,CS:SECT_LEFT ;get sectors left to transfer OR AX,AX ;set flags JNZ INOUT_EM_C ;go back to transfer some sectors INOUT_EM_X2: ;revert to original stack POP DI ;get old SP POP SI ;get old SS CLI ;disable interrupts MOV SS,SI ;restore old SS MOV SP,DI ;restore old SP STI ;enable interrupts RET ;return to IRPT_EXIT INOUT_EM_XE: ;some error with INT 15H MOV CS:EM_STAT,AX ;save error status for debugging MOV RH.RH4_CNT,0 ;indicate no sectors transferred MOV AX,STAT_CRC ;indicate CRC error JMP INOUT_EM_X2 ;fix stack and exit INOUT ENDP DW 40 DUP (?) ;stack for extended memory I/O EM_STACK LABEL WORD SUBTTL Boot Record PAGE ;-----------------------------------------------------------------------; ; Adjust the assembly-time instruction counter to a paragraph ; ; boundary ; ;-----------------------------------------------------------------------; IF ($-START) MOD 16 ORG ($-START) + 16 - (($-START) MOD 16) ENDIF VDISK EQU $ ;start of virtual disk buffer VDISKP EQU ($-START) / PARA_SIZE ;length of program in paragraphs ;-----------------------------------------------------------------------; ; If this VDISK is in extended memory, this address is passed ; ; back to DOS as the end address that is to remain resident. ; ; ; ; It this VDISK is not in extended memory, the VDISK buffer ; ; begins at this address, and the address passed back to DOS ; ; as the end address that is to remain resident is this address ; ; plus the length of the VDISK buffer. ; ;-----------------------------------------------------------------------; BOOT_RECORD LABEL BYTE ;Format of Boot Record documented in ;DOS Technical Reference Manual DB 0,0,0 ;3-byte jump to boot code (not bootable) DB 'VDISK1.0' ;8-byte vendor identification BOOT_BPB LABEL BYTE ;boot record copy of BIOS parameter block DW ? ;number of bytes per disk sector DB ? ;sectors per allocation unit DW ? ;number of reserved sectors (for boot record) DB ? ;number of File Allocation Table (FAT) copies DW ? ;number of root directory entries DW ? ;total number of sectors DB ? ;media descriptor byte DW ? ;number of sectors occupied by a single FAT ;end of boot record BIOS Parameter block ;The following three words mean nothing to VDISK, they are placed here ;to conform to the DOS standard for boot records. DW 8 ;sectors per track DW 1 ;number of heads DW 0 ;number of hidden sectors ;The following word is the 16-bit kilobyte address of the first byte in ;extended memory that is not occupied by a VDISK buffer ;It is placed into this location so that other users of extended memory ;may find where all the VDISKs end. ;This field may be accessed by moving the boot record of the First extended ;memory VDISK from absolute location 10 0000H. Before assuming that the ;value below is valid, the vendor ID (constant VDISK) should be verified ;to make sure that SOME VDISK has been installed. ;For example, if two VDISKs are installed, one 320KB and one 64KB, the ;address calculations are as follows: ;Extended memory start address = 100000H (1024KB) ;Start addr of 1st VDISK buffer = 100000H (1024KB) ;Length of 1st VDISK buffer = 050000H ( 320KB) ;End addr of 1st VDISK buffer = 14FFFFH ;Start addr of 2nd VDISK buffer = 150000H (1344KB) ;Length of 2nd VDISK buffer = 010000H ( 64KB) ;End addr of 2nd VDISK buffer = 15FFFFH ;First byte after all VDISKs = 160000H (1408KB) ;Divide by 1024 = 0580H (1408D) ;Content of BOOT_EM = 0580H BOOT_EM_OFF EQU $-BOOT_RECORD ;offset from 10 0000H of the following word BOOT_EM DW 1024 ;KB addr of first free byte of extended memory ;-----------------------------------------------------------------------; ; Part 2 of Initialization (executed last) ; ;-----------------------------------------------------------------------; ;Initialization is divided into two parts. ;INIT_P1 is overlaid by the virtual disk buffer ;INIT_P1 is executed first, then jumps to INIT_P2. INIT_P2 returns to caller. ;Exercise caution if extending the initialization part 2 code. ;It overlays the area immediately following the boot sector. ;If this section of code must be expanded, make sure it fits into the minimum ;sector size of 128 bytes. ;Label TEST_LENGTH must equate to a non-negative value (TEST_LENGTH >= 0). ;If this code it must be extended beyond the 128 byte length of the boot sector, ;move all of INIT_P2 before label VDISK. ;Registers at entry to INIT_P2 (set up at end of INIT_P1): ; BL = media control byte from BPB (for FAT) ; CX = number of FAT copies ; DX = number of bytes in one FAT - 3 ; SI = OFFSET of Volume Label field ; ES:DI = VDISK buffer address of first FAT sector ; CS = DS = VDISK code segment INIT_P2 PROC ;second part of initialization ASSUME DS:CSEG ;DS set in INIT_P1 ;Initialize File Allocation Table(s) (FATs) INIT_P2_FAT: ;set up one FAT, sector number in AX PUSH CX ;save loop counter on stack MOV AL,BL ;media control byte STOSB ;store media control byte, increment DI MOV AX,0FFFFH ;bytes 2 and 3 of FAT are 0FFH STOSW MOV CX,DX ;FAT size in bytes - 3 XOR AX,AX ;value to store in remainder of FAT REP STOSB ;clear remainder of FAT POP CX ;get loop counter off stack LOOP INIT_P2_FAT ;loop for all copies of the FAT ;Put the volume label in the first directory entry MOV CX,VOL_LABEL_LEN ;length of volume directory entry REP MOVSB ;move volume id to directory ;Zero the remainder of the directory MOV AX,DIR_ENTRY_SIZE ;length of 1 directory entry MUL BPB_DIRN ;* number entries = bytes of directory SUB AX,VOL_LABEL_LEN ;less length of volume label MOV CX,AX ;length of rest of directory XOR AX,AX REP STOSB ;clear directory to nulls RET ;return with AX=0 INIT_P2 ENDP PATCH_AREA DB 5 DUP ('PATCH AREA ') TEST_LENGTH EQU 128-($-VDISK) ;if negative, boot record has too much ;data area, move some fields below VDISK ;-----------------------------------------------------------------------; ; All fields that must remain resident after device driver ; ; initialization must be defined before this point. ; ;-----------------------------------------------------------------------; DB 'The IBM Personal Computer Virtual Disk Device Driver, ' DB 'Version 1.00 (C)Copyright IBM Corp 1984' DB 'Licensed Material - Program Property of IBM. ' DB 'Author: Dick Dievendorff ' BUFF_SIZE DW 0 ;desired VDISK buffer size in kilobytes MIN_MEMORY_LEFT DW 64 ;minimum amount of system memory (kilobytes) ;that must remain after VDISK is installed FIRST_EM_SW DB ? ;0FFH if this is the first device driver ;to be installed in extended memory ;00H if another VDISK extended memory driver ;has been installed FIRST_VDISK DW ? ;segment address of 1st VDISK device driver PARA_PER_KB DW 1024/PARA_SIZE ;paragraphs in one kilobyte C1024 DW 1024 ;bytes in one kilobyte DIRE_SIZE DW DIR_ENTRY_SIZE ;bytes in one directory entry DIR_SECTORS DW ? ;number of sectors of directory ERR_FLAG DB 0 ;error indicators to condition messages ERR_BSIZE EQU 80H ;buffer size adjusted ERR_SSZ EQU 40H ;sector size adjusted ERR_DIRN EQU 20H ;number of directory entries adjusted ERR_PASS EQU 10H ;some adjustment made that requires ;recomputation of values previously computed ERR_SSZB EQU ERR_SSZ+ERR_PASS ;sector size altered this pass ERR_SYSSZ EQU 08H ;system storage too small for VDISK ERR_SWTCH EQU 04H ;invalid switch character ERR_EXTSW EQU 02H ;extender card switches don't match memory size SUBTTL Initialization, Part one PAGE ;-----------------------------------------------------------------------; ; Command Code 0 - Initialization ; ; At entry, DS:BX point to request header, AX = 0 ; ;-----------------------------------------------------------------------; ;Initialization is divided into two parts. ;This part, executed first, is later overlaid by the VDISK buffer. INIT_P1 PROC ;first part of initialization MOV DX,SS ;save stack segment register MOV CX,SP ;save stack pointer register CLI ;inhibit interrupts while changing SS:SP MOV AX,CS ;move CS to SS through AX MOV SS,AX MOV SP,OFFSET MSGEND ;end of VDISKMSG ADD SP,STACK_SIZE ;+ length of our stack STI ;allow interrupts PUSH DX ;save old SS register on new stack PUSH CX ;save old SP register on new stack CALL GET_PARMS ;get parameters from CONFIG.SYS line PUSH CS POP DS ;set DS = CS ASSUME DS:CSEG CALL APPLY_DEFAULTS ;supply any values not specified CALL DETERMINE_START ;compute start address of VDISK buffer CALL VALIDATE ;validate parameters CALL COPY_BPB ;Copy BIOS Parameter Block to boot record CALL VERIFY_EXTENDER ;Verify that extender card switches are right TEST ERR_FLAG,ERR_EXTSW ;are switches wrong? JNZ INIT_P1_A ;if so, exit with messages CMP EM_SW,0 ;extended memory requested? JE INIT_P1_A ;jump if not TEST ERR_FLAG,ERR_SYSSZ ;is system too small for VDISK? JNZ INIT_P1_A ;if so, don't do extended memory init CALL UPDATE_AVAIL ;update AVAIL_HI and AVAIL_LO to reflect ;addition of extended memory VDISK CALL FORMAT_VDISK ;construct a boot record, FATs and ;directory in storage immediately ;following this device driver CALL MOVE_VDISK ;move formatted boot record, FATs, ;and directory to extended memory CALL UPDATE_BOOT ;place the end address of ALL VDISKs ;in the boot record of the first VDISK CMP FIRST_EM_SW,0 ;is this the first extended memory VDISK? JE INIT_P1_A ;no, exit CALL STEAL_INT19 ;point INT 19H to this VDISK INIT_P1_A: CALL FILL_RH ;fill in INIT request header CALL WRITE_MESSAGES ;display all messages POP CX ;get old SP from stack POP DX ;get old SS from stack CLI ;disable interrupts while changing SS:SP MOV SS,DX ;restore stack segment register MOV SP,CX ;restore stack pointer register STI ;enable interrupts ;-----------------------------------------------------------------------; ; INIT_P2 must be short enough to fit into the boot sector ; ; (minimum size of boot sector is 128 bytes), so we set up ; ; as many pointers as we can to help keep INIT_P2 short. ; ; ; ; ES:DI = storage address of first FAT sector ; ; BL = media control byte ; ; CX = number of FAT copies ; ; DX = number of bytes in one FAT, less 3 ; ; SI = offset of VOL label field ; ;-----------------------------------------------------------------------; MOV ES,START_BUFFER_PARA ;start paragraph of VDISK buffer MOV AX,BPB_RES ;number of reserved sectors MUL BPB_SSZ ;* sector size MOV DI,AX ;ES:DI point to FAT start MOV BL,BPB_MCB ;media control byte MOV CL,BPB_FATN ;number of FAT copies XOR CH,CH MOV AX,BPB_FATSZ ;FAT size in sectors MUL BPB_SSZ ;* sector size = total FAT bytes SUB AX,3 ;-3 (FEFFFF stored by code) MOV DX,AX MOV SI,OFFSET VOL_LABEL ;point to VOL label directory entry JMP INIT_P2 ;jump to second part of initialization ;this is redundant if the VDISK is in ;extended memory, but is executed anyway SUBTTL GET_PARMS Parameter Line Scan PAGE ;-----------------------------------------------------------------------; ;GET_PARMS gets the parameters from the CONFIG.SYS statement ; ; ; ;Register usage: ; ; DS:SI indexes parameter string ; ; AL contains character from parameter string ; ; CX value from GET_NUMBER ; ;-----------------------------------------------------------------------; ASSUME DS:NOTHING ;DS:BX point to Request Header GET_PARMS PROC ;get parameters from CONFIG.SYS line PUSH DS ;save DS LDS SI,RH.RH0_BPBA ;DS:SI point to all after DEVICE= ;in CONFIG.SYS line XOR AL,AL ;not at end of line ;Skip until first delimiter is found. There may be digits in the path string. ;DS:SI points to \pathstring\VDISK.SYS nn nn nn ;The character following VDISK.SYS may have been changed to a null (00H). ;All letters have been changed to uppercase. GET_PARMS_A: ;skip to DOS delimiter character CALL GET_PCHAR ;get parameter character into AL JZ GET_PARMS_X ;get out if end of line encountered OR AL,AL ;test for null JZ GET_PARMS_B CMP AL,' ' JE GET_PARMS_B CMP AL,',' JE GET_PARMS_B CMP AL,';' JE GET_PARMS_B CMP AL,'+' JE GET_PARMS_B CMP AL,'=' JE GET_PARMS_B CMP AL,TAB JNE GET_PARMS_A ;skip until delimiter or CR GET_PARMS_B: ;now pointing to first delimiter PUSH SI ;save pointer, used to rescan for /E CALL SKIP_TO_DIGIT ;skip to first digit JZ GET_PARMS_C ;found EOL, no digits remain CALL GET_NUMBER ;extract digits, convert to binary MOV CS:BUFF_SIZE,CX ;store buffer size CALL SKIP_TO_DIGIT ;skip to next digit JZ GET_PARMS_C ;found EOL, no digits remain CALL GET_NUMBER ;extract digits, convert to binary MOV CS:BPB_SSZ,CX ;store sector size CALL SKIP_TO_DIGIT ;skip to next digit JZ GET_PARMS_C ;found EOL, no digits remain CALL GET_NUMBER ;extract digits, convert to binary MOV CS:BPB_DIRN,CX ;store number of directory entries GET_PARMS_C: POP SI ;set for rescan for /E XOR AL,AL ;not at EOL now MOV CS:EM_SW,0 ;indicate no /E found GET_PARMS_D: ;scan for / CALL GET_PCHAR JZ GET_PARMS_X ;exit if end of line CMP AL,'/' ;found slash? JNE GET_PARMS_D ;no, continue scan CALL GET_PCHAR ;get char following slash CMP AL,'E' ;don't have to test for lower case E, ;letters have been changed to upper case JNE GET_PARMS_E ;not 'E' MOV CS:EM_SW,AL ;indicate /E found JMP GET_PARMS_D ;continue forward scan GET_PARMS_E: ;/ found, not 'E' OR CS:ERR_FLAG,ERR_SWTCH ;indicate invalid switch character JMP GET_PARMS_D ;continue scan GET_PARMS_X: ;premature end of line POP DS ;restore DS RET GET_PCHAR PROC ;internal proc to get next character into AL CMP AL,CR ;carriage return already encountered? JE GET_PCHAR_X ;don't read past end of line LODSB ;get char from DS:SI, increment SI CMP AL,CR ;is the char a carriage return? JE GET_PCHAR_X ;yes, set Z flag at end of line CMP AL,LF ;no, is it a line feed? GET_PCHAR_X: ;attempted read past end of line RET GET_PCHAR ENDP ;returns char in AL CHECK_NUM PROC ;check AL for ASCII digit CMP AL,'0' ;< '0'? JB CHECK_NUM_X ;exit if it is CMP AL,'9' ;> '9'? JA CHECK_NUM_X ;exit if it is CMP AL,AL ;set Z flag to indicate numeric CHECK_NUM_X: RET ;Z set if numeric, NZ if not numeric CHECK_NUM ENDP SKIP_TO_DIGIT PROC ;skip to first numeric character CALL CHECK_NUM ;is current char a digit? JZ SKIP_TO_DIGIT_X ;if so, skip is complete CALL GET_PCHAR ;get next character from line JNZ SKIP_TO_DIGIT ;loop until first digit or CR or LF RET ;character is CR or LF SKIP_TO_DIGIT_X: CMP AL,0 ;digit found, force NZ RET SKIP_TO_DIGIT ENDP C10 DW 10 GN_ERR DB ? ;zero if no overflow in accumulation GET_NUMBER PROC ;convert string of digits to binary value XOR CX,CX ;accumulate number in CX MOV CS:GN_ERR,CL ;no overflow yet GET_NUMBER_A: ;accumulate next digit SUB AL,'0' ;convert ASCII to binary CBW ;clear AH XCHG AX,CX ;previous accumulation in AX, new digit in CL MUL CS:C10 ;DX:AX := AX*10 OR CS:GN_ERR,DL ;set GN_ERR <> 0 if overflow ADD AX,CX ;add new digit from XCHG AX,CX ;number now in CX CALL GET_PCHAR ;get next character CALL CHECK_NUM ;see if it was numeric JZ GET_NUMBER_A ;continue accumulating CMP CS:GN_ERR,0 ;did we overflow? JE GET_NUMBER_B ;if not, we're done XOR CX,CX ;return zero (always invalid) if overflow GET_NUMBER_B: RET ;number in CX, next char in AL GET_NUMBER ENDP GET_PARMS ENDP SUBTTL APPLY_DEFAULTS PAGE ;-----------------------------------------------------------------------; ; APPLY_DEFAULTS supplies any parameter values that the user ; ; failed to specify ; ;-----------------------------------------------------------------------; ASSUME DS:CSEG APPLY_DEFAULTS PROC XOR AX,AX CMP BUFF_SIZE,AX ;is buffer size zero? JNE APPLY_DEFAULTS_A ;no, user specified something MOV BUFF_SIZE,DFLT_BSIZE ;supply default buffer size OR ERR_FLAG,ERR_BSIZE ;indicate buffersize adjusted APPLY_DEFAULTS_A: CMP BPB_SSZ,AX ;is sector size zero? JNE APPLY_DEFAULTS_B ;no, user specified something MOV BPB_SSZ,DFLT_SSZ ;supply default sector size OR ERR_FLAG,ERR_SSZ ;indicate sector size adjusted APPLY_DEFAULTS_B: CMP BPB_DIRN,AX ;are directory entries zero? JNE APPLY_DEFAULTS_C ;no, user specified something MOV BPB_DIRN,DFLT_DIRN ;supply default directory entries OR ERR_FLAG,ERR_DIRN ;indicate directory entries adjusted APPLY_DEFAULTS_C: RET APPLY_DEFAULTS ENDP SUBTTL DETERMINE_START address of VDISK buffer PAGE ;-----------------------------------------------------------------------; ; DETERMINE_START figures out the starting address of the VDISK ; ; buffer ; ;-----------------------------------------------------------------------; ASSUME DS:CSEG DETERMINE_START PROC ;If extended memory is NOT being used, the VDISK buffer immediately ;follows the resident code. ;If extended memory IS being used, START_BUFFER_PARA becomes the ;end of device driver address passed back to DOS. MOV AX,CS ;start para of VDISK code ADD AX,VDISKP ;+ length of resident code MOV START_BUFFER_PARA,AX ;save as buffer start para CMP EM_SW,0 ;is extended memory requested? JE DETERMINE_START_X ;if not, we're done here ;If this is the first extended memory VDISK device driver to be installed, ;the start address for I/O is 1 megabyte. ;If one or more extended memory VDISK device drivers have been installed, ;the start address for I/O for THIS device driver is acquired from the ;fields AVAIL_LO and AVAIL_HI in the FIRST VDISK device driver. ;The first extended memory VDISK device driver is located by INT 19H's vector. MOV FIRST_EM_SW,0FFH ;indicate first VDISK device driver MOV FIRST_VDISK,CS ;segment addr of first VDISK PUSH DS ;preserve DS XOR AX,AX MOV DS,AX ;set DS = 0 ASSUME DS:INT_VEC MOV AX,DS:BOOT_VECS ;get segment addr of INT 19H routine MOV DS,AX ;to DS ASSUME DS:NOTHING PUSH CS POP ES ;set ES = CS MOV SI,OFFSET VOL_LABEL ;DS:SI point to VOL label field ;in first VDISK (if present) MOV DI,SI ;ES:DI point to VOL label field of ;this VDISK MOV CX,VOL_LABEL_LEN ;length of volume label REP CMPSB ;does INT 19H vector point to a VDISK ;device driver? JNE DETERMINE_START_A ;jump if this is the first VDISK ;Another extended memory VDISK device driver has been installed. ;Its AVAIL_LO and AVAIL_HI are the first free byte of extended memory. MOV CS:FIRST_EM_SW,0 ;indicate not first device driver MOV CS:FIRST_VDISK,DS ;save pointer to 1st device driver ;Copy AVAIL_LO and AVAIL_HI from first VDISK to this VDISK MOV SI,OFFSET AVAIL_LO ;DS:SI point to AVAIL_LO in first VDISK MOV DI,SI ;ES:DI point to AVAIL_LO in this VDISK MOVSW ;copy AVAIL_LO from first to this VDISK MOVSB ;copy AVAIL_HI DETERMINE_START_A: ;copy AVAIL_LO and AVAIL_HI to START_EM POP DS ;set DS = CS MOV SI,OFFSET AVAIL_LO ;source offset MOV DI,OFFSET START_EM_LO ;destination offset MOVSW ;move AVAIL_LO to START_EM_LO MOVSB ;move AVAIL_HI to START_EM_HI DETERMINE_START_X: RET DETERMINE_START ENDP SUBTTL VALIDATE parameters PAGE ;-----------------------------------------------------------------------; ; VALIDATE adjusts parameters as necessary ; ;-----------------------------------------------------------------------; VAL_SSZ_TBL LABEL WORD ;table of valid sector sizes VAL_SSZ_S DW 128 ;smallest valid sector size DW 256 VAL_SSZ_L DW 512 ;largest valid sector size VAL_SSZ_N EQU ($-VAL_SSZ_TBL)/2 ;number of table entries ASSUME DS:CSEG VALIDATE PROC ;validate parameters MOV BPB_AUSZ,1 ;initial allocation unit is 1 sector CALL VAL_BSIZE ;validate buffer size CALL VAL_SSZ ;validate (adjust if necessary) BPB_SSZ VALIDATE_A: AND ERR_FLAG,255-ERR_PASS ;indicate nothing changed this pass MOV AX,BPB_SSZ ;sector size CWD ;clear DX for division DIV WPARA_SIZE ;sector size/para size MOV PARAS_PER_SECTOR,AX ;number of paragraphs/sector MOV AX,BUFF_SIZE ;requested buffersize in KB MUL C1024 ;DX:AX = buffer size in bytes DIV BPB_SSZ ;/sector size = # sectors MOV BPB_SECN,AX ;store number of sectors CALL VAL_DIRN ;validate number of directory entries TEST ERR_FLAG,ERR_PASS ;may have reset sector size JNZ VALIDATE_A ;recompute directory & FAT sizes CALL VAL_FAT ;compute FAT entries, validity test TEST ERR_FLAG,ERR_PASS ;if cluster size altered this pass JNZ VALIDATE_A ;recompute directory & FAT sizes ;Make certain buffer size is large enough to contain: ; boot sector(s) ; FAT sector(s) ; directory sector(s) ; at least 1 data cluster MOV AL,BPB_FATN ;number of FAT copies CBW ;clear AH MUL BPB_FATSZ ;* sectors for 1 FAT = FAT sectors ADD AX,BPB_RES ;+ reserved sectors ADD AX,DIR_SECTORS ;+ directory sectors MOV CL,BPB_AUSZ ;get sectors/cluster XOR CH,CH ;CX = sectors in one cluster ADD AX,CX ;+ one data cluster CMP BPB_SECN,AX ;compare with sectors available JAE VALIDATE_X ;jump if enough sectors CMP DIR_SECTORS,1 ;down to 1 directory sector? JBE VALIDATE_C ;can't let it go below 1 MOV AX,BPB_SSZ ;sector size CWD ;clear DX for division DIV DIRE_SIZE ;sectorsize/dir entry size = entries/sector SUB BPB_DIRN,AX ;reduce directory entries by 1 sector OR ERR_FLAG,ERR_DIRN ;indicate directory entries adjusted JMP VALIDATE_A ;retry with new directory entries number VALIDATE_C: ;not enough space for any VDISK OR ERR_FLAG,ERR_SYSSZ VALIDATE_X: RET SUBTTL VAL_BSIZE Validate buffer size PAGE ;-----------------------------------------------------------------------; ; VAL_BSIZE adjusts the buffer size as necessary ; ;-----------------------------------------------------------------------; VAL_BSIZE PROC CALL GET_MSIZE ;determine memory available to VDISK ;returns available KB in AX OR AX,AX ;is any memory available at all? JNZ VAL_BSIZE_B ;yes, continue OR ERR_FLAG,ERR_SYSSZ ;indicate system too small for VDISK MOV BUFF_SIZE,1 ;set up minimal values to continue init MOV AX,VAL_SSZ_S ;smallest possible sector size MOV BPB_SSZ,AX MOV BPB_DIRN,4 ;4 directory entries RET VAL_BSIZE_B: ;some memory is available CMP AX,BUFF_SIZE ;is available memory >= requested? JAE VAL_BSIZE_C ;if so, we're done MOV BUFF_SIZE,AX ;give all available memory OR ERR_FLAG,ERR_BSIZE ;indicate buffersize adjusted VAL_BSIZE_C: RET GET_MSIZE PROC ;determine memory available to VDISK ;returns KB available in AX CMP EM_SW,0 ;extended memory? JE GET_MSIZE_2 ;use non-extended memory routine MOV AH,EM_MEMSIZE ;function code to AH INT EM_INT ;get extended memory size in AX JC GET_MSIZE_Z ;if error, no extended memory installed MUL C1024 ;DX,AX = bytes of extended memory ADD DX,10H ;DX,AX = high addr of extended memory+1 SUB AX,AVAIL_LO ;- address of first available byte SBB DL,AVAIL_HI ;is number of free bytes DIV C1024 ;AX = number of whole free kilobytes RET GET_MSIZE_2: ;non-extended memory size determination ;Compute AX = total system size, - (VDISK end address + 64KB) MOV AX,START_BUFFER_PARA ;paragraph end of VDISK code XOR DX,DX ;clear for division DIV PARA_PER_KB ;KB address of load point ADD DX,0FFFFH ;round upward to KB boundary ADC AX,MIN_MEMORY_LEFT ;pick up CY and the 64KB we should leave PUSH AX ;save across interrupt INT MEM_SIZE ;get total system size POP DX ;amount of total that we can't use SUB AX,DX ;available space to VDISK JNC GET_MSIZE_X ;exit if positive GET_MSIZE_Z: XOR AX,AX ;indicate no memory available GET_MSIZE_X: ;exit from memory size determination RET GET_MSIZE ENDP VAL_BSIZE ENDP SUBTTL VAL_SSZ Validate Sector Size PAGE ;-----------------------------------------------------------------------; ; VAL_SSZ validates sector size, adjusting if necessary ; ;-----------------------------------------------------------------------; VAL_SSZ PROC ;validate sector size MOV BX,BPB_SSZ ;requested sector size MOV CX,VAL_SSZ_N ;number of table entries MOV SI,OFFSET VAL_SSZ_TBL ;DS:SI point to table start VAL_SSZ_A: LODSW ;get table entry, step table pointer CMP AX,BX ;is value in table? JE VAL_SSZ_X ;exit if value found LOOP VAL_SSZ_A ;loop until table end MOV BX,DFLT_SSZ ;get default sector size MOV BPB_SSZ,BX ;set sector size to default value OR ERR_FLAG,ERR_SSZ ;indicate sector size adjusted VAL_SSZ_X: ;Compute the maximum number of sectors that can be moved in 64KB (less one) ;Restricting moves to this amount avoids 64KB boundary problems. XOR DX,DX MOV AX,0FFFFH ;64KB - 1 DIV BX ;/sector size MOV MAX_CNT,AX ;max sectors in one move RET VAL_SSZ ENDP SUBTTL VAL_DIRN Validate number of directory entries PAGE ;-----------------------------------------------------------------------; ; VAL_DIRN validates and adjusts the number of directory entries. ; ; ; ; Minimum is MIN_DIRN, maximum is MAX_DIRN. If outside these ; ; limits, DFLT_DIRN is used. ; ; ; ; The number of directory entries is rounded upward to fill ; ; a sector ; ;-----------------------------------------------------------------------; VAL_DIRN PROC MOV AX,BPB_DIRN ;requested directory entries CMP AX,MIN_DIRN ;if less than minimum JB VAL_DIRN_A ;use default instead CMP AX,MAX_DIRN ;if <= maximum JBE VAL_DIRN_B ;accept value as provided VAL_DIRN_A: MOV AX,DFLT_DIRN ;use default directory entries OR ERR_FLAG,ERR_DIRN ;indicate directory entries adjusted VAL_DIRN_B: ;AX is number of directory entries MUL DIRE_SIZE ;* 32 = bytes of directory requested DIV BPB_SSZ ;/ sector size = # of directory sectors OR DX,DX ;test remainder for zero JZ VAL_DIRN_C ;jump if exact fit INC AX ;increment directory sectors OR ERR_FLAG,ERR_DIRN ;indicate directory entries adjusted VAL_DIRN_C: ;make sure enough sectors available MOV DX,BPB_SECN ;total sectors on media SUB DX,BPB_RES ;less reserved sectors SUB DX,2 ;less minimum FAT and 1 data sector CMP AX,DX ;if directory sectors <= available JLE VAL_DIRN_D ;use requested amount MOV AX,1 ;use only one directory sector OR ERR_FLAG,ERR_DIRN ;indicate directory entries adjusted VAL_DIRN_D: MOV DIR_SECTORS,AX ;save number of directory sectors MUL BPB_SSZ ;dir sectors * sector size = dir bytes DIV DIRE_SIZE ;dir bytes / entry size = entries MOV BPB_DIRN,AX ;store adjusted directory entries RET VAL_DIRN ENDP SUBTTL VAL_FAT Validate File Allocation Table (FAT) PAGE ;-----------------------------------------------------------------------; ;VAL_FAT computes: ; ;BPB_FATSZ, the number of sectors required per FAT copy ; ; ; ;Each FAT entry is 12 bits long, for a maximum of 4095 FAT entries. ; ;(A few FAT entries are reserved, so the highest number of FAT entries ; ;we permit is 0FE0H.) With large buffer sizes and small sector sizes, ; ;we have more allocation units to describe than a 12-bit entry will ; ;describe. If the number of FAT entries is too large, the sector size ; ;is increased (up to a maximum of 512 bytes), and then the allocation ; ;unit (cluster) size is doubled, until we have few enough allocation ; ;units to be properly described in 12 bits. ; ; ; ;This computation is slightly conservative in that the FAT entries ; ;necessary to describe the FAT sectors are included in the computation. ; ;-----------------------------------------------------------------------; VAL_FAT PROC MOV AX,BPB_SECN ;total number of sectors SUB AX,BPB_RES ;don't count boot sector(s) SUB AX,DIR_SECTORS ;don't count directory sectors JG VAL_FAT_A ;jump if some remaining MOV BPB_SSZ,DFLT_SSZ ;force default sector size OR ERR_FLAG,ERR_SSZ+ERR_PASS ;indicate sector size adjusted JMP SHORT VAL_FAT_X ;recompute all values VAL_FAT_A: XOR DX,DX ;clear DX for division MOV CL,BPB_AUSZ ;CX = sectors/cluster XOR CH,CH DIV CX ;whole number of clusters in AX ADD DX,0FFFFH ;set carry if remainder ADC AX,0 ;increment AX if remainder CMP AX,MAX_FATE ;number of FAT entries too large? JBE VAL_FAT_C ;no, continue MOV AX,BPB_SSZ ;pick up current sector size CMP AX,VAL_SSZ_L ;already at largest permitted? JE VAL_FAT_B ;yes, can't make it any larger SHL BPB_SSZ,1 ;double sector size OR ERR_FLAG,ERR_SSZB ;indicate sector size adjusted JMP SHORT VAL_FAT_X ;recompute all sizes with new BPBSSZ VAL_FAT_B: ;sector size is at maximum SHL BPB_AUSZ,1 ;double allocation unit size OR ERR_FLAG,ERR_PASS ;indicate another pass required JMP SHORT VAL_FAT_X ;recompute values VAL_FAT_C: ;FAT size = 1.5 * number of clusters MOV CX,AX ;number of clusters SHL AX,1 ;* 2 ADD AX,CX ;* 3 SHR AX,1 ;* 1.5 ADC AX,3 ;add 3 bytes for first 2 FAT entries ;(media descriptor and FFFFH), and CY XOR DX,DX ;clear DX for division DIV BPB_SSZ ;FAT size/sector size ADD DX,0FFFFH ;set carry if remainder ADC AX,0 ;round upward MOV BPB_FATSZ,AX ;number of sectors for 1 FAT copy VAL_FAT_X: RET VAL_FAT ENDP VALIDATE ENDP SUBTTL COPY_BPB Copy BPB to Boot Record PAGE ;-----------------------------------------------------------------------; ; COPY_BPB copies the BIOS Parameter Block (BPB) ; ; to the VDISK Boot Record ; ;-----------------------------------------------------------------------; ASSUME DS:CSEG COPY_BPB PROC ;Copy BBP to Boot Record PUSH DS POP ES ;set ES = DS MOV CX,BPB_LEN ;length of BPB MOV SI,OFFSET BPB ;source offset MOV DI,OFFSET BOOT_BPB ;target offset REP MOVSB ;copy BPB to boot record RET COPY_BPB ENDP SUBTTL VERIFY_EXTENDER PAGE ;-----------------------------------------------------------------------; ; VERIFY_EXTENDER makes sure that if an Expansion Unit is ; ; installed, the memory size switches on the Extender Card ; ; are correctly set. ; ;-----------------------------------------------------------------------; ASSUME DS:CSEG EXT_P210 EQU 0210H ;write to latch expansion bus data ;read to verify expansion bus data EXT_P213 EQU 0213H ;Expansion Unit status VERIFY_EXTENDER PROC NOP MOV DX,EXT_P210 ;Expansion bus data port address MOV AX,5555H ;set data pattern OUT DX,AL ;write 55H to control port PUSH DX ;load data line POP DX ;load data line IN AL,DX ;recover data CMP AH,AL ;did we recover the same data? JNE VERIFY_EXTENDER_X ;if not, no extender card NOT AX ;set AX = 0AAAAH OUT DX,AL ;write 0AAH to control port PUSH DX ;load data line POP DX ;load data line IN AL,DX ;recover data CMP AH,AL ;did we recover the same data? JNE VERIFY_EXTENDER_X ;if not, no extender card ;Expansion Unit is present. ;Determine what the switch settings should be on the Extender Card INT MEM_SIZE ;get system memory size in KB in AX ADD AX,63D ;memory size + 63K MOV CL,6 ;2^6 = 64 SHR AX,CL ;divide by 64 ;AX is highest segment address MOV AH,AL ;save number of segments ;Read Expander card switch settings MOV DX,EXT_P213 ;expansion unit status IN AL,DX ;read status ;bits 7-4 (hi nibble) are switches MOV CL,4 ;shift count SHR AL,CL ;shift switches to bits 3-0 of AL CMP AH,AL ;do switches match memory size? JE VERIFY_EXTENDER_X ;yes, exit normally OR ERR_FLAG,ERR_EXTSW ;indicate switch settings are wrong VERIFY_EXTENDER_X: RET VERIFY_EXTENDER ENDP SUBTTL UPDATE_AVAIL PAGE ;-----------------------------------------------------------------------; ; UPDATE_AVAIL updates the address of the first byte in extended ; ; memory not used by any VDISK buffer ; ;-----------------------------------------------------------------------; UPDATE_AVAIL PROC ;update AVAIL_LO and AVAIL_HI of first VDISK MOV AX,BUFF_SIZE ;number of KB of VDISK buffer MUL C1024 ;DX,AX = number of bytes of VDISK buffer PUSH DS MOV DS,FIRST_VDISK ;set DS to first VDISK ADD DS:AVAIL_LO,AX ;update first available byte location ADC DS:AVAIL_HI,DL POP DS RET UPDATE_AVAIL ENDP SUBTTL FORMAT_VDISK PAGE ;-----------------------------------------------------------------------; ; This Request Header is used by MOVE_VDISK to move the ; ; first few sectors of the virtual disk (boot, FAT, and ; ; Directory) into extended memory. ; ;-----------------------------------------------------------------------; MOVE_RH DB MOVE_RH_L ;length of request header DB 0 ;sub unit DB 8 ;output operation DW 0 ;status DQ ? ;reserved for DOS DB ? ;media descriptor byte MOVE_RHO DW ? ;offset of data transfer address MOVE_RHS DW ? ;segment of data transfer address MOVE_RHCNT DW ? ;count of sectors to transfer DW 0 ;starting sector number MOVE_RH_L EQU $-MOVE_RH ;length of request header ;-----------------------------------------------------------------------; ; FORMAT_VDISK formats the boot sector, FAT, and directory of an ; ; extended memory VDISK in storage immediately following ; ; VDISK code, in preparation for moving to extended memory. ; ;-----------------------------------------------------------------------; FORMAT_VDISK PROC ;format boot record, FATs and directory MOV AX,CS ;compute 20-bit address MUL WPARA_SIZE ;16 * segment ADD AX,OFFSET MSGEND ;+ offset ADC DL,0 ;pick up carry ADD AX,STACK_SIZE ;plus stack size ADC DL,0 ;pick up carry DIV WPARA_SIZE ;split into segment(AX)&offset(DX) MOV MOVE_RHS,AX ;save in Request Header for move MOV MOVE_RHO,DX MOV DI,DX ;offset to DI MOV ES,AX ;segment to ES ;copy the boot record MOV SI,OFFSET BOOT_RECORD ;point to source field MOV AX,BPB_RES ;number of reserved sectors MUL BPB_SSZ ;* sector size = length of boot records MOV CX,AX ;length to CX for move REP MOVSB ;move boot record(s) ;format the FAT(s) MOV CL,BPB_FATN ;number of FATs XOR CH,CH FORMAT_VDISK_A: ;set up one FAT PUSH CX ;save loop counter on stack MOV AL,BPB_MCB ;media control byte STOSB ;store media control byte, increment DI MOV AX,0FFFFH ;bytes 2 and 3 of FAT are 0FFH STOSW MOV AX,BPB_FATSZ ;number of sectors per FAT MUL BPB_SSZ ;* sector size = length of FAT in bytes SUB AX,3 ;less the 3 bytes we've stored MOV CX,AX ;count to CX XOR AX,AX REP STOSB ;clear remainder of FAT POP CX ;get loop counter off stack LOOP FORMAT_VDISK_A ;loop for all copies of the FAT ;Format the directory MOV SI,OFFSET VOL_LABEL ;point to volume label MOV CX,VOL_LABEL_LEN ;length of volume directory entry REP MOVSB ;move volume id to directory MOV AX,DIR_ENTRY_SIZE ;length of 1 directory entry MUL BPB_DIRN ;* number entries = bytes of directory SUB AX,VOL_LABEL_LEN ;less length of volume label MOV CX,AX ;CX = length of rest of directory XOR AX,AX REP STOSB ;clear directory to nulls RET FORMAT_VDISK ENDP SUBTTL MOVE_VDISK PAGE ;-----------------------------------------------------------------------; ; MOVE_VDISK moves the formatted boot sector, FAT, and directory ; ; into extended memory. ; ;-----------------------------------------------------------------------; MOVE_VDISK PROC MOV AL,BPB_FATN ;number of FAT copies CBW ;clear AH MUL BPB_FATSZ ;number of FAT sectors ADD AX,BPB_RES ;+ reserved sectors ADD AX,DIR_SECTORS ;+ directory sectors MOV MOVE_RHCNT,AX ;store as I/O length MOV BX,OFFSET MOVE_RH ;DS:BX point to request header PUSH DS ;make sure DS gets preserved CALL INOUT ;move to extended memory POP DS RET MOVE_VDISK ENDP SUBTTL UPDATE_BOOT PAGE ;-----------------------------------------------------------------------; ; UPDATE_BOOT updates the BOOT_EM word in the first extended ; ; memory VDISK (address 10 001EH) to show the kilobyte address ; ; of the first extended memory byte not used by any VDISK buffer. ; ;-----------------------------------------------------------------------; UPDATE_BOOT PROC PUSH DS MOV DS,FIRST_VDISK ;set DS to first VDISK MOV AX,DS:AVAIL_LO ;24-bit end address of all VDISKs MOV DL,DS:AVAIL_HI XOR DH,DH POP DS DIV C1024 ;address / 1024 MOV BOOT_EM,AX ;store in temporary location MOV AX,2 ;length of block move is 2 bytes MOV TGT.DESC_LMT,AX MOV SRC.DESC_LMT,AX MOV AX,PARA_SIZE ;16 MOV CX,CS ;our segment address MUL CX ;16 * segment address ADD AX,OFFSET BOOT_EM ;+ offset of source data ADC DL,0 ;pick up any carry MOV SRC.DESC_BASEL,AX ;store source base address MOV SRC.DESC_BASEH,DL MOV TGT.DESC_BASEL,BOOT_EM_OFF ;offset of BOOT_EM MOV TGT.DESC_BASEH,10H ;1 megabyte MOV CX,1 ;move 1 word PUSH CS POP ES MOV SI,OFFSET GDT ;ES:DI point to global descriptor table MOV AH,EM_BLKMOVE ;function code INT EM_INT ;move BOOT_EM to 10 001EH RET UPDATE_BOOT ENDP SUBTTL STEAL_INT19 PAGE ;-----------------------------------------------------------------------; ; STEAL_INT19 changes the INT 19H vector to point to this VDISK ; ; so that subsequent extended memory VDISKS may locate the ; ; AVAIL_HI and AVAIL_LO fields to determine their buffer start ; ; addresses. ; ;-----------------------------------------------------------------------; STEAL_INT19 PROC PUSH DS XOR AX,AX MOV DS,AX ;set DS = 0 ASSUME DS:INT_VEC CLI ;disable interrupts LES DI,DS:BOOT_VEC ;get original vector's content MOV CS:INTV19O,DI ;save original vector MOV CS:INTV19S,ES MOV DS:BOOT_VECO,OFFSET VDISK_INT19 ;offset of new INT routine MOV DS:BOOT_VECS,CS ;segment of new INT routine STI ;enable interrupts again POP DS ;restore DS RET STEAL_INT19 ENDP SUBTTL FILL_RH Fill in Request Header PAGE ;-----------------------------------------------------------------------; ; FILL_RH fills in the Request Header returned to DOS ; ;-----------------------------------------------------------------------; ASSUME DS:CSEG FILL_RH PROC ;fill in INIT Request Header fields MOV CX,START_BUFFER_PARA ;segment end of VDISK resident code MOV AX,PARAS_PER_SECTOR ;paragraphs per sector MUL BPB_SECN ;* number of sectors ADD AX,CX ;+ starting segment MOV DX,AX ;DX is segment of end VDISK buffer CMP EM_SW,0 ;if extended memory not requested JE FILL_RH_A ;skip DX adjustment MOV DX,CX ;end of code segment addr FILL_RH_A: ;DX is proper ending segment address MOV AL,1 ;number of units TEST ERR_FLAG,ERR_SYSSZ+ERR_EXTSW ;if bypassing install JZ FILL_RH_B ;jump if installing driver MOV DX,CS ;segment of end address XOR AL,AL ;number of units is zero FILL_RH_B: PUSH DS ;preserve DS LDS BX,RH_PTRA ;get Request Header addr in DS:BX MOV RH.RH0_NUN,AL ;store number of units (0 or 1) MOV RH.RH0_ENDO,0 ;end offset is always zero MOV RH.RH0_ENDS,DX ;end of VDISK or end of buffer MOV RH.RH0_BPBO,OFFSET BPB_PTR MOV RH.RH0_BPBS,CS ;BPB array address POP DS ;restore DS RET FILL_RH ENDP SUBTTL WRITE_MESSAGES and associated routines PAGE ;-----------------------------------------------------------------------; ; WRITE_MESSAGE writes a series of messages to the standard ; ; output device showing the VDISK parameter values actually used. ; ;-----------------------------------------------------------------------; ;These external references are resolved by messages in VDISKMSG ;Messages placed in separate assembly to ease translation effort. ;Each message string is terminated with a '$' EXTRN IMSG:BYTE ;VDISK installing virtual disk EXTRN ERRM1:BYTE ; Buffer size adjusted CR LF EXTRN ERRM2:BYTE ; Sector size adjusted CR LF EXTRN ERRM3:BYTE ; Directory entries adjusted CR LF EXTRN ERRM4:BYTE ;VDISK not installed - insufficient memory CR LF EXTRN ERRM5:BYTE ; Invalid switch character CR LF EXTRN ERRM6:BYTE ;VDISK not installed - Extender card switches ; do not match system memory size CR LF EXTRN MSG1:BYTE ; Buffer size: EXTRN MSG2:BYTE ; KB CR LF EXTRN MSG3:BYTE ; Sector size: EXTRN MSG4:BYTE ; Directory entries: EXTRN MSGCRLF:BYTE ;CR LF EXTRN MSGEND:BYTE ;last byte of VDISKMSG CHAR4 DB 'nnnn$' ;build 4 ASCII decimal digits ASSUME DS:CSEG WRITE_MESSAGES PROC ;display all messages MSG IMSG ;'VDISK Version 1.0 virtual disk $' ;If DOS Version 3 is in use, the Request Header contains a drive code ;that is displayed to show which drive letter was assigned to this ;VDISK. This field is not present in the DOS Version 2 Request Header. MOV AH,DOS_VERS ;get DOS version call INT DOS ;invoke DOS CMP AL,3 ;DOS Version 3 or greater? JB WRITE_MESSAGES_A ;no, bypass drive letter PUSH DS ;preserve DS LDS BX,RH_PTRA ;get Request Header Address MOV DL,RH.RH0_DRIV ;get drive code ADD DL,'A' ;convert to drive letter POP DS ;restore DS MOV AH,DOS_PCHR ;function code to write character in DL INT DOS ;display drive letter MOV DL,':' ;display trailing colon INT DOS WRITE_MESSAGES_A: MSG MSGCRLF ;end the first line ;If any of the user specified values has been adjusted, issue an ;appropriate message TEST ERR_FLAG,ERR_BSIZE ;was buffersize adjusted? JZ WRITE_MESSAGES_B ;if not, skip message MSG ERRM1 ;buffer size adjusted WRITE_MESSAGES_B: TEST ERR_FLAG,ERR_SSZ ;was sector size adjusted? JZ WRITE_MESSAGES_C ;if not, skip message MSG ERRM2 ;sector size adjusted WRITE_MESSAGES_C: TEST ERR_FLAG,ERR_DIRN ;were directory entries adjusted? JZ WRITE_MESSAGES_D ;if not, skip message MSG ERRM3 ;directory entries adjusted WRITE_MESSAGES_D: TEST ERR_FLAG,ERR_SWTCH ;was an invalid switch character found? JZ WRITE_MESSAGES_E ;if not, skip message MSG ERRM5 ;invalid switch character WRITE_MESSAGES_E: TEST ERR_FLAG,ERR_SYSSZ ;is system size too small to install? JZ WRITE_MESSAGES_F ;if not, bypass error message MSG ERRM4 ;too large for system storage RET ;skip messages showing adjusted sizes WRITE_MESSAGES_F: TEST ERR_FLAG,ERR_EXTSW ;extender card switches wrong? JZ WRITE_MESSAGES_G ;if not, bypass error message MSG ERRM6 ;extender card switches wrong msg RET ;skip remaining messages WRITE_MESSAGES_G: ;display adjusted size messages MSG MSG1 ;buffer size: MOV DX,BUFF_SIZE ;buffer size in binary CALL STOR_SIZE ;convert binary to ASCII decimal MSG CHAR4 ;print 4 decimals MSG MSG2 ;KB,CR,LF MSG MSG3 ;sector size: MOV DX,BPB_SSZ CALL STOR_SIZE ;convert binary to ASCII decimal MSG CHAR4 ;print 4 decimals MSG MSGCRLF ;finish off line MSG MSG4 ;directory entries: MOV DX,BPB_DIRN ;number of directory entries CALL STOR_SIZE MSG CHAR4 ;print 4 decimals MSG MSGCRLF ;finish off the line MSG MSGCRLF ;one more blank line to set it off RET ;return to INIT_P1 ;SHOW_MSG displays a string at DS:DX on the standard output device ;String is terminated by a $ SHOW_MSG PROC ;display string at DS:DX PUSH AX ;preserve AX across call MOV AH,DOS_PSTR ;DOS function code INT DOS ;invoke DOS print string function POP AX ;restore AX RET SHOW_MSG ENDP ;STOR_SIZE converts the content of DX to 4 decimal characters in CHAR4 ;(DX must be <= 9999) STOR_SIZE PROC ;convert DX to 4 decimals in CHAR4 ;develop 4 packed decimal digits in AX XOR AX,AX ;clear result register MOV CX,16 ;shift count STOR_SIZE_B: SHL DX,1 ;shift high bit into carry ADC AL,AL ;double AL, carry in DAA ;adjust for packed decimal XCHG AL,AH ADC AL,AL ;double high byte, carry in DAA XCHG AL,AH LOOP STOR_SIZE_B ;AX contains 4 packed decimal digits PUSH CS POP ES ;point ES:DI to output string MOV DI,OFFSET CHAR4 MOV CX,1310H ;10H in CL is difference between blank and zero ;13H in CH is decremented and ANDed to force ;last character not to be zero suppressed PUSH AX ;save AX on stack MOV DL,AH ;2 decimals to DL CALL STOR_SIZE_2 ;display DL as 2 decimal characters POP DX ;bring low 2 decimals into DL STOR_SIZE_2: ;display DL as 2 decimal characters MOV DH,DL ;save 2 decimals in DH SHR DL,1 ;shift high order decimal right to low position SHR DL,1 SHR DL,1 SHR DL,1 CALL STOR_SIZE_1 ;display low nibble of DL MOV DL,DH ;get low decimal from pair STOR_SIZE_1: ;display low nibble of DL as 1 decimal char AND DL,0FH ;clear high nibble JZ STOR_SIZE_Z ;if digit is significant, XOR CL,CL ;defeat zero suppression STOR_SIZE_Z: DEC CH ;decrement zero suppress counter AND CL,CH ;always display least significant digit OR DL,'0' ;convert packed decimal to ASCII SUB DL,CL ;zero suppress (nop or change '0' to ' ') MOV AL,DL ;char to DL STOSB ;store char at ES:DI, increment DI RET STOR_SIZE ENDP WRITE_MESSAGES ENDP INIT_P1 ENDP ;end of INIT part one ;VDISKMSG is linked beyond this module. CSEG ENDS END