Simtel MSDOS 1992 June/SIMTEL_0692.cdr/msdos/sysutl/stepdos.arc/STEPDOS.ASM

Assembly Source File | 1987-11-08 | 66.1 KB | 2,511 lines

;
;       ***********************************************************
;       *                                                         *
;       *                   S  T  E  P  D  O  S                   *
;       *                                                         *
;       *                        Rev 1.0                          *
;       *                                                         *
;       *                      Nov 7, 1987                        *
;       *                                                         *
;       *               Mike Parker - CIS 70270,161               *
;       *                                                         *
;       *  This program allows you to step through the execution  *
;       *  of another program by intercepting all calls to DOS    *
;       *  INT 21H. A window will pop up displaying all register  *
;       *  values and a short description of the DOS function     *
;       *  being called. Program execution will continue when     *
;       *  you press a key. You can optionally break again after  *
;       *  the DOS function completes so you can see the result   *
;       *  code in the AX register along with important flags.    *
;       *                                                         *
;       ***********************************************************
;
; To run, type STEPDOS <filename>
;  where <filename> is the full pathname of an EXE or COM file.
;

        PAGE    60,132
        TITLE   'Step DOS Calls'
        NAME    STEPDOS


TESTING    EQU    0

BG         EQU    10H               ; BG sets background color (10h = BLUE)

BLACK      EQU    00H + BG
BLUE       EQU    01H + BG
GREEN      EQU    02H + BG
CYAN       EQU    03H + BG
RED        EQU    04H + BG
MAGENTA    EQU    05H + BG
BROWN      EQU    06H + BG
WHITE      EQU    07H + BG
GRAY       EQU    08H + BG
LTBLUE     EQU    09H + BG
LTGREEN    EQU    0AH + BG
LTCYAN     EQU    0BH + BG
LTRED      EQU    0CH + BG
LTMAGENTA  EQU    0DH + BG
YELLOW     EQU    0EH + BG
HIWHITE    EQU    0FH + BG
;
CR         EQU    13
LF         EQU    10
BIGR       EQU    1352H             ; 'R' key
SMALLR     EQU    1372H             ; 'r'
BIGS       EQU    1F53H             ; 'S' key
SMALLS     EQU    1F73H             ; 's'
ESCAPE     EQU    011BH
HOME       EQU    4700H
UPARROW    EQU    4800H
PGUP       EQU    4900H
LEFTARROW  EQU    4B00H
RIGHTARROW EQU    4D00H
XEND       EQU    4F00H
DOWNARROW  EQU    5000H
PGDN       EQU    5100H
;
BLANK      EQU    32
BRDROW     EQU    205
BRDCOL     EQU    186
ULC        EQU    201
URC        EQU    187
LLC        EQU    200
LRC        EQU    188
;
REGBX      EQU    00                ; offsets on saved register stack
REGCX      EQU    02
REGDX      EQU    04
REGDI      EQU    06
REGSI      EQU    08
REGBP      EQU    10
REGES      EQU    12
REGFL      EQU    14
;
IF TESTING
INT21OFF   EQU    0e0h*4            ; during testing an unused INT is used
ELSE
INT21OFF   EQU    21h*4
ENDIF

Code    SEGMENT PUBLIC PARA 'CODE'

        ASSUME  CS:Code, DS:Code

Main:                               ; starting point
        mov     DI,DS
        mov     BX,2
        mov     SI,[BX]             ; paragraphs of memory in system from PSP
        sub     SI,DI               ; paragraphs beyond segment
        cmp     SI,1000h            ; more than 64K available ?
        jb      main_1
        mov     SI,1000h            ; yes, only use 64K
main_1:
        add     SI,DI               ; si = DS + number paragraphs in DS
        mov     BX,ES               ; bx = PSP base
        sub     BX,SI
        neg     BX                  ; bx = number of paragraphs needed
        mov     AH,4ah              ; modify memory block size
        int     21h
;
; Copy command line from PSP to local area
;
        mov     AX,CS
        mov     ES,AX               ; change ES to be local area
;
        mov     SI,80h
        mov     CL,[SI]             ; get command line character count
        or      CL,CL               ; zero char count in cmd line?
        jnz     notzcl
        mov     AX,CS
        mov     DS,AX
        mov     DX,OFFSET Umsg
        mov     AH,9
        int     21h
        jmp     exit
notzcl:
        xor     CH,CH
        inc     SI
        mov     DI,OFFSET PSPstr
rep     movsb                       ; copy command line
        xor     AL,AL
        stosb                       ; <NULL> terminator at end
;
        mov     BX,002ch
        mov     BX,[BX]             ; get segment addr of environment from PSP
;
        mov     AX,CS
        mov     DS,AX
        mov     SegEnv,BX           ; save in EXEC control block
;
        mov     DX,OFFSET INITmsg
        mov     AH,9
        int     21h
;
; Calculate starting address on screen for window
;
        mov     BX,OFFSET W1        ; window parameters
        mov     AX,[BX].leftrow
        mul     BytesPL             ; multiply by bytes per line
        mov     CX,[BX].leftcol
        shl     CX,1                ; times 2 for attribute byte
        add     AX,CX
        mov     SI,AX               ; starting physical address of window
        mov     [BX].startmem,AX    ; save it for later
;
; Calculate size of window in bytes to allocate memory
;
        mov     AX,[BX].rightcol
        inc     AX
        sub     AX,[BX].leftcol
        mov     [BX].xwidth,AX
        mov     CX,[BX].rightrow
        inc     CX
        sub     CX,[BX].leftrow
        mov     [BX].height,CX
        mul     CL                  ; AX = nbr of bytes of screen area
        shl     AX,1                ; times 2 to get attributes also
;
; Do DOS call to allocate memory
;
        mov     CL,4
        shr     AX,CL               ; divide by 16 to get # paragraphs
        inc     AX                  ; handle any remainder
        mov     BX,AX
        mov     AH,48h              ; 'allocate memory' DOS call
        int     21h
        mov     Winseg,AX           ; save returned segment
        jnc     cpynam
        mov     DX,OFFSET Memerr    ; ERROR - display string
        mov     AH,9
        int     21h
        jmp     exit                ;  and terminate
;
; Copy target program name
;
cpynam:
        mov     SI,OFFSET PSPstr + 1
        mov     DI,OFFSET Filename
        xor     CX,CX               ; zero char count
fnlp:
        cmp     BYTE PTR [SI],' '   ; look for <SP>
        jz      fndn
        cmp     BYTE PTR [SI],00    ;  or <NULL> terminator
        jz      fndn
        movsb
        inc     CX                  ; count number of filename char's
        jmp     fnlp
fndn:
        or      CX,CX
        jnz     gotfn
        mov     DX,OFFSET Findmsg   ; error if zero filename length
        mov     AH,9
        int     21h
        jmp     freemem
gotfn:
        xor     AL,AL
        stosb
        mov     FNsize,CX
;
; Copy command line string
; SI -> first parameter after filename
;
        mov     DI,OFFSET CLstr + 1
        xor     CX,CX               ; zero char count
cllp:
        cmp     BYTE PTR [SI],00    ; look for <NULL> terminator
        jz      dncl
        movsb
        inc     CX                  ; count number of cmd line char's
        jmp     cllp
dncl:
        xor     AL,AL               ; store <NULL>
        stosb
        mov     AL,CR               ;  and <CR>
        stosb
        mov     CLstr,CL            ; store cmd line count
;
; Build EXEC control block
;
        mov     SegCmd,OFFSET CLstr
        mov     SegCmd+2,DS
        mov     FCBptr1,OFFSET FCB1
        mov     FCBptr1+2,DS
        mov     FCBptr2,OFFSET FCB2
        mov     FCBptr2+2,DS
;
; Parse first parameter
;
        mov     SI,OFFSET CLstr + 1
        mov     DI,OFFSET FCB1
        mov     AL,01               ; scan past separators
        mov     AH,29h
        int     21h
;
; Parse second parameter
;
        mov     DI,OFFSET FCB2
        mov     AL,01               ; scan past separators
        mov     AH,29h
        int     21h
;
; Check for '.' in target program filename
;
        mov     DI,OFFSET Filename
        mov     CX,FNsize           ; get program filename size
        mov     AL,'.'
repne   scasb
        jz      fndext
;
; No extention found, try appending '.COM'
;
        mov     SI,OFFSET COMstr
        mov     DI,OFFSET Filename
        add     DI,FNsize
        mov     CX,4
rep     movsb
;
; Try to OPEN the target program to see if it exists before we change
; the Int 21h vector and EXEC it.
;
        mov     AH,3dh
        mov     AL,00               ; access code
        mov     DX,OFFSET Filename
        int     21h
        jnc     clsfile             ; jump if file found
;
; OPEN with '.COM' extention failed, try appending '.EXE'
;
        mov     SI,OFFSET EXEstr
        mov     DI,OFFSET Filename
        add     DI,FNsize
        mov     CX,4
rep     movsb
;
; Try to OPEN the '.EXE' version of the file
;
fndext:
        mov     AH,3dh
        mov     AL,00               ; access code
        mov     DX,OFFSET Filename
        int     21h
        jnc     clsfile
        mov     DX,OFFSET Findmsg   ; not found
        mov     AH,9
        int     21h
        jmp     freemem
;
; Found the file, now close it and do EXEC function
;
clsfile:
        mov     BX,AX               ; move file handle
        mov     AH,3eh
        int     21h
;
; Redirect INT 21h
;
redirect:
        push    ES
        cli
        mov     AX,0
        mov     ES,AX
        mov     AX,OFFSET New21
        xchg    AX,ES:[INT21OFF]
        mov     Save21,AX
        mov     AX,CS
        xchg    AX,ES:[INT21OFF+2]
        mov     Save21+2,AX
        sti
        pop     ES
;
; Execute target program
;
        mov     DX,OFFSET Filename
        mov     BX,OFFSET Param_Block
        mov     AH,4bh
        mov     AL,0
        mov     SP,OFFSET Tstack
        int     21h
        jnc     execdn
;
; Failed to execute target program. Display message and quit
;
        mov     AX,CS
        mov     DS,AX
        mov     DX,OFFSET Execmsg
        mov     AH,9
        int     21h
;
execdn:
        mov     AX,CS               ; restore segment registers
        mov     DS,AX
        mov     ES,AX
        mov     SS,AX
        mov     SP,OFFSET Pstack
;
; Restore INT 21h vector
;
        cli
        mov     AX,0
        mov     ES,AX
        mov     AX,Save21
        mov     ES:[INT21OFF],AX
        mov     AX,Save21+2
        mov     ES:[INT21OFF+2],AX
        sti
;
; Free allocated memory from window save area
;
freemem:
        mov     ES,Winseg
        mov     AH,49h
        int     21h
exit:
        mov     AH,4ch              ; terminate process
        mov     AL,00
        int     21h                 ; won't return

;
; INT 21h will be redirected to here
;
New21:
        push    AX                  ; use USERS'S stack for first 2 words
        push    DS
;
        mov     AX,CS               ; now switch to internal stack
        mov     DS,AX
        mov     SSsave,SS
        mov     SPsave,SP
        mov     SS,AX
        mov     SP,OFFSET Pstack
;
        pushf
        push    ES
        push    BP
        push    SI
        push    DI
        push    DX
        push    CX
        push    BX
        mov     BP,SP               ; save base pointer to display reg's
        mov     ES,AX
        mov     AL,Run_Flg
        test    AL,0ffh             ; should we stop and display?
        jnz     runit
        jmp     norun               ; no, restore registers and leave
runit:
        cld                         ; clear direction flag for string operations
        call    Get_User_Regs       ; recover registers left on user's stack
;
        mov     AL,Skip_Flg
        test    AL,0ffh             ; skip certain functions?
        jz      noskip              ; no, continue
        mov     AX,AXsave           ; get USER's AX register with function code
        cmp     AH,Skip_Typ         ; compare upper half to type to skip
        jnz     clrskip
        jmp     norun               ; don't want to break on this one again
clrskip:
        mov     AL,00               ; skip flag was set but this is new
        mov     Skip_Flg,AL         ;  function, so break from now on
noskip:
        call    Open_Window
        call    Show_Regs
        call    Show_Help
        call    Disp_Text           ; Display description string of DOS function
;
        call    Get_Key             ; wait for a key pressed
        call    Disp_Key            ; dispatch to key handler
        call    Close_Window
norun:
        pop     BX
        pop     CX
        pop     DX
        pop     DI
        pop     SI
        pop     BP
        pop     ES
        popf
        mov     SP,SPsave
        mov     SS,SSsave
        pop     DS
        pop     AX

IFE TESTING
        pushf
        call    CS:[DWORD PTR Save21]
ENDIF

        push    AX                  ; use USERS'S stack for first 2 words
        push    DS
;
        mov     AX,CS               ; now switch to internal stack
        mov     DS,AX
        mov     SSsave,SS
        mov     SPsave,SP
        mov     SS,AX
        mov     SP,OFFSET Pstack
;
        pushf
        push    ES
        push    BP
        push    SI
        push    DI
        push    DX
        push    CX
        push    BX
        mov     BP,SP               ; save base pointer to display reg's
        mov     ES,AX
        cld                         ; clear direction flag for string operations
        call    Get_User_Regs       ; recover registers left on user's stack
        xor     AL,AL
        xchg    AL,Ret_Flg          ; read value and clear flag for next time
        test    AL,0ffh             ; is flag set to display return value?
        jz      nostop
;
        call    Open_Window
        call    Show_Regs
        call    Disp_Ret            ; display return code in AX and flags
        call    Get_Key             ; wait for a key pressed
        call    Close_Window
nostop:
        pop     BX
        pop     CX
        pop     DX
        pop     DI
        pop     SI
        pop     BP
        pop     ES
        popf
        mov     SP,SPsave
        mov     SS,SSsave
        pop     DS
        pop     AX
        retf    2

;
; Display return code in AX, carry and zero flags
;
Disp_Ret:
        mov     DX,OFFSET RCStr
        mov     DI,14
        mov     AX,AXsave
        call    OutWord
;
        mov     DX,OFFSET CFStr
        mov     DI,13
        add     DI,DX
        mov     AL,'0'
        test    FLsave,0001         ; carry flag is least significant bit
        jz      dcy
        inc     AL                  ; carry was set so change to '1'
dcy:
        mov     [DI],AL             ; store it in string
        add     CX,0015h            ; move cursor position
        mov     BX,OFFSET W1
        mov     AH,HIWHITE
        call    WPrint
;
        mov     DX,OFFSET ZFStr
        mov     DI,12
        add     DI,DX
        mov     AL,'0'
        test    FLsave,0040h        ; test zero flag
        jz      dzf
        inc     AL                  ; zero was set so change to '1'
dzf:
        mov     [DI],AL             ; store it in string
        add     CX,0010h            ; move cursor position
        mov     BX,OFFSET W1
        mov     AH,HIWHITE
        call    WPrint
;
        mov     CX,0816h            ; display some help
        mov     DX,OFFSET HlpStr4
        mov     AH,YELLOW
        call    WPrint
        ret

RCStr   db      'Return Code = XXXXH'
        db      0

CFStr   db      'Carry Flag = X'
        db      0

ZFStr   db      'Zero Flag = X'
        db      0

;
; Recover registers on USER'S stack
;
Get_User_Regs:
        push    ES
        les     BX,Ssave
        mov     AX,ES:[BX]          ; get DS
        mov     DSsave,AX
        mov     AX,ES:[BX+2]        ; get AX
        mov     AXsave,AX
        mov     AX,ES:[BX+4]        ; get IP
        mov     IPsave,AX
        mov     AX,ES:[BX+6]        ; get CS
        mov     CSsave,AX
        mov     AX,[BP+REGFL]       ; get FLAGS off local stack
        mov     FLsave,AX
        pop     ES
        ret

;
; Display register names in window
;
Show_Regs:
        mov     BX,OFFSET W1        ; window
        mov     CX,0001h            ; cursor position - row, col
        mov     DX,OFFSET RegStr1   ; message address
        mov     AH,YELLOW           ; attribute
        call    WPrint
;
        add     CX,0100h            ; go down one row
        mov     DX,OFFSET RegStr2
        mov     AH,WHITE
        call    WPrint
;
; Display register values
;
        add     CX,0100h            ; down a row
        mov     AX,AXsave           ; get user's AX
        call    Whexwd              ; display hex word
;
        push    BP                  ; save base pointer for string display
        mov     DX,6                ; number of registers to show this loop
disreg:
        add     CX,0005h            ; move to next register field
        mov     AX,[BP]
        call    Whexwd              ; display hex word
        add     BP,2
        dec     DX
        jnz     disreg
;
        add     CX,0005h            ; move to next register field
        mov     AX,SPsave           ; display SP
        add     AX,4                ; add for 2 pushes we did
        call    Whexwd
;
        add     CX,0005h            ; move to next register field
        mov     AX,DSsave           ; display DS
        call    Whexwd
;
        add     CX,0005h            ; display ES
        mov     AX,[BP]
        call    Whexwd
;
        add     CX,0005h
        mov     AX,SSsave           ; display SS
        call    Whexwd
;
        add     CX,0005h
        mov     AX,CSsave           ; display CS
        call    Whexwd
;
        add     CX,0005h
        mov     AX,IPsave           ; display IP
        call    Whexwd
;
        add     CX,0005h
        mov     AX,FLsave           ; display FLAGS
        call    Whexwd
        pop     BP                  ; restore base pointer so display routines
                                    ;  can use it
        ret

;
; Display HELP in Window
;
Show_Help:
        mov     CX,0801h            ; cursor position - row, col
        mov     AH,LTRED            ; attribute for char
        mov     AL,'S'
        call    WChar               ; write one character with attribute
;
        add     CX,0001h            ; add 1 to column number
        mov     DX,OFFSET HlpStr1   ; message address
        mov     AH,WHITE
        call    WPrint
;
        add     CX,0017h            ; move column number
        mov     AH,LTRED            ; attribute for char
        mov     AL,'R'
        call    WChar               ; write one character with attribute
;
        add     CX,0001h            ; move column number
        mov     DX,OFFSET HlpStr2
        mov     AH,WHITE
        call    WPrint
;
        add     CX,000dh
        mov     AH,LTRED
        mov     AL,'E'
        call    WChar
;
        add     CX,0001h
        mov     AH,LTRED
        mov     AL,'S'
        call    WChar
;
        add     CX,0001h
        mov     AH,LTRED
        mov     AL,'C'
        call    WChar
;
        add     CX,0001h
        mov     DX,OFFSET HlpStr3
        mov     AH,WHITE
        call    WPrint
        ret

;
; HextoDec converts a word in AX to an ASCII string
; Entry:
;      AX = word to convert
; Exit:
;      SI = Pointer to last two character of ASCII string in 'Astr'
;
HextoDec:
         push   AX
         push   CX
         push   DX
         push   DI
;
         mov    DI,OFFSET Astr
         mov    CX,10000
         xor    DX,DX
         div    CX                  ; num / 10000
         add    AL,'0'
         stosb
         mov    AX,DX
         mov    CX,1000
         xor    DX,DX
         div    CX                  ; num / 1000
         add    AL,'0'
         stosb
         mov    AX,DX
         mov    CX,100
         xor    DX,DX
         div    CX                  ; num / 100
         add    AL,'0'
         stosb
         mov    AX,DX
         mov    CX,10
         xor    DX,DX
         div    CX                  ; num / 10
         add    AL,'0'
         stosb
         mov    AX,DX
         add    AL,'0'
         stosb
         xor    AL,AL               ; <NULL> terminator in string
         stosb
         sub    DI,3                ; back up pointer
         mov    SI,DI
;
         pop    DI
         pop    DX
         pop    CX
         pop    AX
         ret

;
; Display the text description of the current DOS function code
;
Disp_Text:
        mov     AX,AXsave           ; get user's function code
        cmp     AH,63h              ; is it in range?
        jnb     not_fnd             ; jump if no
        mov     DI,OFFSET FCtbl
        mov     CX,LENFC / 6        ; number of entries
cmpdt:
        cmp     AH,[DI+1]           ; is this the right function?
        jz      dtexec
        add     DI,6                ; no, point to next
        loop    cmpdt
not_fnd:
        mov     DX,OFFSET STRUN
        call    Disp_Str
        ret

dtexec:
        mov     DX,[DI+2]           ; get pointer to string
        call    [WORD PTR DI+4]     ; go to display routine
        ret

;
; Display string of DOS function code description
;
; Entry:
;       DX = pointer to string
;
Disp_Str:
        mov     CX,0501h
        mov     BX,OFFSET W1
        mov     AH,HIWHITE
        call    WPrint
        ret

;
; Only one string must be inserted.
; It is pointed to by user's DS:DX.
; Entry:
;      DX = text string containing description of function call
;      DI = offset within local string (DX) to put user's (DS:DX)
;      CX = max length before you will hit right side of Window
;
One_String:
        add     DI,DX
        push    DS
        mov     DS,DSsave
        mov     SI,[BP+REGDX]       ; get USER's DS:DX value
rep     movsb                       ; copy user's memory to text string
        pop     DS
        call    Disp_Str
        ret

;
; Convert users's DS and DX to ASCII, imbed them in target string
; Entry:
;      DX = pointer to string
;      DI = offset where to put converted DS:DX
;
OutDSDX:
        add     DI,DX
        mov     AX,DSsave           ; get user's DS
        call    Shexwrd
        inc     DI                  ; skip past ':'
        mov     AX,[BP+REGDX]       ; get user's DX
        call    Shexwrd
        call    Disp_Str
        ret

;
; Convert word in AX to ASCII, imbed it in target string
; Entry:
;      AX = word to convert
;      DX = pointer to string
;      DI = offset where to put converted AX
;
OutWord:
        add     DI,DX
        call    Shexwrd
        call    Disp_Str
        ret

;
; Convert 'AL' to ASCII and imbed it in target string
; Entry:
;      DX = target string
;      DI = offset to put converted 'AL'
;      AL = value to convert
;
OutByte:
        add     DI,DX
        call    Shexbyt
        call    Disp_Str
        ret

;
; Routines to build string for display - some values need to be filled in
;
; Entry:
;       DX = pointer to string
;
Disp_02:
Disp_04:
Disp_05:
        mov     DI,DX
        add     DI,22               ; offset this many into string
        mov     AX,[BP+REGDX]       ; DL register has char to output
        call    Shexbyt             ; convert it to ASCII
        mov     [DI+8],AL           ; show hex byte
        call    Disp_Str
        ret

;
; Direct Keyboard/Display I/O
;
Disp_06:
        call    Disp_Str
        mov     AX,[BP+REGDX]       ; DL register has I/O type
        mov     DX,OFFSET STR06I
        cmp     AL,0ffh             ; input character?
        jz      d06io
        mov     DX,OFFSET STR02     ; no, output character in 'DL'
        mov     DI,DX
        add     DI,22               ; offset this many into string
        call    Shexbyt             ; convert it to ASCII
        mov     [DI+8],AL           ; show hex byte
d06io:
        add     CX,0015h
        mov     BX,OFFSET W1
        mov     AH,HIWHITE
        call    WPrint
        ret

;
; Display String
; Entry:
;      DX = pointer to string
;
Disp_09:
Disp_39:
Disp_3a:
Disp_3b:
Disp_3c:
Disp_3d:
Disp_41:
Disp_5a:
Disp_5b:
        mov     DI,18               ; offset where (DS:DX) goes within string
        mov     cx,52               ; max number of char's to fit in window
        call    One_String
        ret

Disp_0a:
Disp_23:
        mov     DI,27
        call    OutDSDX
        ret

;
; Clear Keyboard and Do Function
;
Disp_0c:
        mov     DI,31
        mov     AX,AXsave           ; AL register has function number
        call    OutByte
        ret

;
; Select Disk
;
Disp_0e:
        mov     DI,12
        mov     AX,[BP+REGDX]       ; DL register has char to output
        call    OutByte
        ret

;
; Open File Using FCB
;
Disp_0f:
        mov     DI,23
        call    OutDSDX
        ret

;
; Close File Using FCB
;
Disp_10:
        mov     DI,24
        call    OutDSDX
        ret

;
; Search For First Matching File Using FCB
;
Disp_11:
        mov     DI,44
        call    OutDSDX
        ret

;
; Search For Next Matching File Using FCB
;
Disp_12:
        mov     DI,43
        call    OutDSDX
        ret

;
; Delete File Using FCB
; Create File Using FCB
; Rename File Using FCB
;
Disp_13:
Disp_16:
Disp_17:
        mov     DI,25
        call    OutDSDX
        ret

;
; Read Sequential File Record Using FCB
;
Disp_14:
        mov     DI,41
        call    OutDSDX
        ret

;
; Write Sequential File Record Using FCB
;
Disp_15:
        mov     DI,42
        call    OutDSDX
        ret

;
; Set Disk Transfer Address
;
Disp_1a:
        mov     DI,29
        call    OutDSDX
        ret

;
; Get FAT Information For Drive
;
Disp_1c:
        mov     DI,30
        mov     AX,[BP+REGDX]       ; DL register has drive number
        call    OutByte
        ret


;
; Read Random File Record Using FCB
; Set Random Record Field Using FCB
;
Disp_21:
Disp_24:
        mov     DI,37
        call    OutDSDX
        ret

;
; Write Random File Record Using FCB
;
Disp_22:
        mov     DI,38
        call    OutDSDX
        ret

;
; Set Interrupt Vector
;
Disp_25:
        mov     DI,DX
        add     DI,21
        mov     AX,AXsave           ; AL has interrupt vector number
        call    Shexbyt
        mov     DI,28
        call    OutDSDX
        ret

;
; Create New Program Segment
;
Disp_26:
        mov     DI,38
        mov     AX,[BP+REGDX]       ; get user's DX
        call    OutWord
        ret

;
; Read Random File Records
;
Disp_27:
        mov     DI,DX
        add     DI,5
        mov     AX,[BP+REGCX]       ; CX register has record count
        call    Shexwrd
        mov     DI,44
        call    OutDSDX
        ret

;
; Write Random File Records
;
Disp_28:
        mov     DI,DX
        add     DI,6
        mov     AX,[BP+REGCX]       ; CX register has record count
        call    Shexwrd
        mov     DI,45
        call    OutDSDX
        ret
;
; Parse Filename
;
Disp_29:
        mov     DI,18               ; offset where (DS:SI) goes within string
        mov     cx,52               ; max number of char's to fit in window
        add     DI,DX
        push    DI                  ; save for scan later
        push    DS
        mov     DS,DSsave
        mov     SI,[BP+REGSI]       ; get USER's DS:SI value
rep     movsb                       ; copy user's memory to text string
        pop     DS
;
; look for <CR> in string and put <NULL> terminator there
;
        pop     DI
        mov     AL,CR
        mov     cx,52
repne   scasb
        jnz     dpf
        dec     DI
        xor     AL,AL
        mov     [DI],AL
dpf:
        call    Disp_Str
        ret

;
; Set Date
;
Disp_2b:
        mov     DI,DX
        add     DI,22
        mov     AX,[BP+REGDX]       ; DX register has month/day
        mov     AL,AH
        xor     AH,AH
        call    HextoDec            ; convert month
        movsb
        movsb
        inc     DI                  ; skip past '/'
        mov     AX,[BP+REGDX]
        xor     AH,AH
        call    HextoDec            ; convert day
        movsb
        movsb
        inc     DI                  ; skip past '/'
        mov     AX,[BP+REGCX]
        call    HextoDec            ; convert year
        movsb
        movsb
        call    Disp_Str
        ret

;
; Set Time
;
Disp_2d:
        mov     DI,DX
        add     DI,33
        mov     AX,[BP+REGCX]       ; CX register has hours/minutes
        mov     AL,AH
        xor     AH,AH
        call    HextoDec            ; convert hours
        movsb
        movsb
        inc     DI                  ; skip past ':'
        mov     AX,[BP+REGCX]
        xor     AH,AH
        call    HextoDec            ; convert minutes
        movsb
        movsb
        inc     DI                  ; skip past ':'
        mov     AX,[BP+REGDX]       ; DX has seconds/hundreds of seconds
        mov     AL,AH
        xor     AH,AH
        call    HextoDec            ; convert seconds
        movsb
        movsb
        inc     DI                  ; skip past ':'
        mov     AX,[BP+REGDX]
        xor     AH,AH
        call    HextoDec            ; convert hundreds
        movsb
        movsb
        call    Disp_Str
        ret

;
; Set Disk Write Verification
;
Disp_2e:
        mov     DI,DX
        add     DI,28
        mov     AX,AXsave           ; AL register has verify switch
        mov     SI,OFFSET OFFstr
        cmp     AL,00               ; AL = 0 means OFF
        jz      verptr
        mov     SI,OFFSET ONstr
        cmp     AL,01               ; AL = 1 means ON
        jz      verptr
        mov     SI,OFFSET Blanks3   ; unknown code
verptr:
        mov     CX,3
rep     movsb
        call    Disp_Str
        ret

;
; Get/Set Control-Break Status
;
Disp_33:
        mov     AX,AXsave           ; AL register has get/set switch
        cmp     AL,01               ; AL = 1 for SET
        jz      setcbs
        cmp     AL,00               ; AL = 0 for GET
        jnz     unk33               ; jump if unknown code
        mov     DX,OFFSET STR33G
unk33:
        call    Disp_Str
        ret

setcbs:
        mov     DX,OFFSET STR33S    ; point to 'SET' string
        mov     DI,DX
        add     DI,25
        mov     AX,[BP+REGDX]       ; DL has set code
        mov     SI,OFFSET OFFstr
        cmp     AL,00               ; AL = 00 means OFF
        jz      gscbs
        mov     SI,OFFSET ONstr
        cmp     AL,01               ; AL = 01 means ON
        jz      gscbs
        mov     SI,OFFSET Blanks3
gscbs:
        mov     CX,3
rep     movsb
        call    Disp_Str
        ret

;
; Get Interrupt Vector
;
Disp_35:
        mov     DI,21
        mov     AX,AXsave           ; AL has interrupt vector number
        call    OutByte
        ret

;
; Get Disk Free Space On Drive
;
Disp_36:
        mov     DI,29
        mov     AX,[BP+REGDX]       ; DL register has drive code
        call    OutByte
        ret

;
; Close File Handle
;
Disp_3e:
        mov     DI,18
        mov     AX,[BP+REGBX]       ; BX register has file handle
        call    OutWord
        ret

;
; Duplicate File Handle
;
Disp_45:
        mov     DI,22
        mov     AX,[BP+REGBX]       ; BX register has file handle
        call    OutWord
        ret

;
; Read From File or Device
;
Disp_3f:
        mov     DI,DX
        add     DI,5
        mov     AX,[BP+REGCX]       ; CX has number of bytes to read
        call    Shexwrd
        mov     DI,37
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret

;
; Write To File or Device
;
Disp_40:
        mov     DI,DX
        add     DI,6
        mov     AX,[BP+REGCX]       ; CX has number of bytes to read
        call    Shexwrd
        mov     DI,36
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret

;
; Move File Pointer
;
Disp_42:
        mov     DI,DX
        add     DI,17
        mov     AX,[BP+REGBX]       ; BX register has file handle
        call    Shexwrd
        add     DI,13
        mov     AX,[BP+REGCX]       ; CX has upper half of offset
        call    Shexwrd
        inc     DI                  ; skip past ':'
        mov     AX,[BP+REGDX]       ; CX has lower half of offset
        call    Shexwrd
        add     DI,7
        mov     AX,AXsave           ; AL has method code
        mov     SI,OFFSET BOFstr
        cmp     AL,00               ; beginning of file?
        jz      mvptr
        mov     SI,OFFSET CURstr
        cmp     AL,01               ; current location?
        jz      mvptr
        mov     SI,OFFSET EOFstr
        cmp     AL,02               ; end of file?
        jz      mvptr
        mov     SI,OFFSET Blanks17  ; unknown
mvptr:
        mov     cx,17               ; string length
rep     movsb
        call    Disp_Str
        ret

;
; Get/Set file attributes
;
Disp_43:
        mov     AX,AXsave           ; user's AX has get/set flag
        cmp     AL,00               ; 'get' code?
        jz      fgptr
        cmp     AL,01               ; 'set' code?
        jz      fsptr
        call    Disp_Str            ; unknown code
        ret
fgptr:
        mov     DX,OFFSET STR43G    ; point to GET string
        jmp     SHORT faptr
;
fsptr:
        mov     DX,OFFSET STR43S    ; point to SET string
faptr:
        mov     DI,18
        mov     cx,52               ; max number of char's to fit in window
        call    One_String
        ret

;
; I/O Control For Devices
;
Disp_44:
        mov     AX,AXsave
        cmp     AL,00
        jz      jd440
        cmp     AL,01
        jz      jd441
        cmp     AL,02
        jz      jd442
        cmp     AL,03
        jz      jd443
        cmp     AL,04
        jz      jd444
        cmp     AL,05
        jz      jd445
        cmp     AL,06
        jz      jd446
        cmp     AL,07
        jz      jd447
        cmp     AL,08
        jz      jd448
        cmp     AL,11
        jz      jd4411
        call    Disp_Str            ; unknown code
        ret

jd440:  jmp     d440
jd441:  jmp     d441
jd442:  jmp     d442
jd443:  jmp     d443
jd444:  jmp     d444
jd445:  jmp     d445
jd446:  jmp     d446
jd447:  jmp     d447
jd448:  jmp     d448
jd4411: jmp     d4411

d440:
        mov     DX,OFFSET STR440    ; Get Info For Device
        mov     DI,20
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d441:
        mov     DX,OFFSET STR441    ; Set Info For Device
        mov     DI,DX
        add     DI,20
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    Shexwrd
        mov     DI,29
        mov     AX,[BP+REGDX]       ; DX has device information
        call    OutWord
        ret
;
d442:
        mov     DX,OFFSET STR442    ; Read From Drive Control Channel
        mov     DI,DX
        add     DI,5
        mov     AX,[BP+REGCX]       ; CX has byte count
        call    Shexwrd
        mov     DI,52
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d443:
        mov     DX,OFFSET STR443    ; Write To Drive Control Channel
        mov     DI,DX
        add     DI,6
        mov     AX,[BP+REGCX]       ; CX has byte count
        call    Shexwrd
        mov     DI,51
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d444:
        mov     DX,OFFSET STR444    ; Read From Control Channel of Drive
        mov     DI,DX
        add     DI,5
        mov     AX,[BP+REGCX]       ; CX has byte count
        call    Shexwrd
        mov     DI,47
        mov     AX,[BP+REGBX]       ; BL has drive
        call    OutByte
        ret
;
d445:
        mov     DX,OFFSET STR445    ; Write To Control Channel of Drive
        mov     DI,DX
        add     DI,6
        mov     AX,[BP+REGCX]       ; CX has byte count
        call    Shexwrd
        mov     DI,46
        mov     AX,[BP+REGBX]       ; BL has drive
        call    OutByte
        ret
;
d446:
        mov     DX,OFFSET STR446    ; Get Input Status of Device
        mov     DI,27
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d447:
        mov     DX,OFFSET STR447    ; Get Output Status of Device
        mov     DI,28
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d448:
        mov     DX,OFFSET STR448    ; Report Whether Device Has Removable Media
        mov     DI,22
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
d4411:
        mov     DX,OFFSET STR4411   ; Set Retries For Device
        mov     DI,DX
        add     DI,23
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    Shexwrd
        add     DI,5
        mov     AX,[BP+REGDX]       ; DX has retry count
        call    Shexwrd
        mov     DI,55
        mov     AX,[BP+REGCX]       ; CX has interval between tries
        call    OutWord
        ret

;
; Force Duplication of Handle
;
Disp_46:
        mov     DI,DX
        add     DI,28
        mov     AX,[BP+REGBX]       ; BX has the existing file handle
        call    Shexwrd
        mov     DI,37
        mov     AX,[BP+REGCX]       ; CX has the second file handle
        call    OutWord
        ret

;
; Get Current Directory
;
Disp_47:
        mov     DI,DX
        add     DI,31
        mov     AX,[BP+REGDX]       ; DL register has drive code
        call    Shexbyt
        add     DI,7
        mov     AX,DSsave
        call    Shexwrd
        inc     DI                  ; skip ':'
        mov     AX,[BP+REGSI]       ; get USER's DS:SI value
        call    Shexwrd
        call    Disp_Str
        ret

;
; Allocate Memory
;
Disp_48:
        mov     DI,9
        mov     AX,[BP+REGBX]       ; BX has the memory requested in paragraphs
        call    OutWord
        ret

;
; Free Allocated Memory
;
Disp_49:
        mov     DI,33
        mov     AX,[BP+REGES]       ; ES has the segment address
        call    OutWord
        ret

;
; Modify Memory Block
;
Disp_4a:
        mov     DI,DX
        add     DI,31
        mov     AX,[BP+REGES]       ; ES has the segment address
        call    Shexwrd
        mov     DI,43
        mov     AX,[BP+REGBX]       ; BX has size in paragraphs
        call    OutWord
        ret

;
; Load or Exececute Program
; Find First Matching File
;
Disp_4b:
Disp_4e:
        mov     DI,29               ; offset where (DS:DX) goes within string
        mov     cx,41               ; max number of char's to fit in window
        call    One_String
        ret

;
; Terminate Process with Return Code
;
Disp_4c:
        mov     DI,35
        mov     AX,Axsave           ; AL register return code
        call    OutByte
        ret

;
; Rename File
;
Disp_56:
        mov     DI,29
        mov     cx,41
        call    One_String          ; display 'old' name
;
        mov     DX,OFFSET STR56N
        mov     DI,DX
        add     DI,29
        push    DS
        mov     DS,[BP+REGES]
        mov     SI,[BP+REGDI]       ; get USER's ES:DI value
        mov     cx,41               ;  to display 'new' name
rep     movsb
        pop     DS
        mov     CX,0601h
        mov     BX,OFFSET W1
        mov     AH,HIWHITE
        call    WPrint
        ret

;
; Get Date and Time of File
;
Disp_57:
        mov     AX,AXsave           ; user's AL has get/set indicator
        cmp     AL,00               ; is it GET?
        jz      gdtptr
        cmp     AL,01               ; is it SET?
        jz      sdtptr
        mov     DI,37               ; unknown function
        mov     AX,[BP+REGBX]       ; file handle
        call    OutWord
        ret
gdtptr:
        mov     DX,OFFSET STR57G
        jmp     SHORT ddtptr
;
sdtptr:
        mov     DX,OFFSET STR57S
ddtptr:
        mov     DI,33
        mov     AX,[BP+REGBX]       ; BX register has file handle
        call    OutWord
        ret

;
; Lock/Unlock File
;
Disp_5c:
        mov     AX,AXsave
        cmp     AL,00               ; 0 = Lock
        jz      dlck
        cmp     AL,01               ; 1 = Unlock
        jz      dunlck
        mov     DI,17
        mov     AX,[BP+REGBX]       ; BX has file handle
        call    OutWord
        ret
;
dlck:
        mov     DX,OFFSET STR5c0
        mov     DI,10
        mov     AX,[BP+REGBX]
        call    OutWord
        ret
;
dunlck:
        mov     DX,OFFSET STR5c1
        mov     DI,12
        mov     AX,[BP+REGBX]
        call    OutWord
        ret


;
; Table of function codes.
; (1st) word is DOS function code (AH),
; (2nd) word is pointer to string to display,
; (3rd) word is subroutine address to handle display of this type function.
;
FCtbl:
        dw      0000h, STR00, Disp_Str
        dw      0100h, STR01, Disp_Str
        dw      0200h, STR02, Disp_02
        dw      0300h, STR03, Disp_Str
        dw      0400h, STR04, Disp_04
        dw      0500h, STR05, Disp_05
        dw      0600h, STR06, Disp_06
        dw      0700h, STR07, Disp_Str
        dw      0800h, STR08, Disp_Str
        dw      0900h, STR09, Disp_09
        dw      0a00h, STR0a, Disp_0a
        dw      0b00h, STR0b, Disp_Str
        dw      0c00h, STR0c, Disp_0c
        dw      0d00h, STR0d, Disp_Str
        dw      0e00h, STR0e, Disp_0e
        dw      0f00h, STR0f, Disp_0f
        dw      1000h, STR10, Disp_10
        dw      1100h, STR11, Disp_11
        dw      1200h, STR12, Disp_12
        dw      1300h, STR13, Disp_13
        dw      1400h, STR14, Disp_14
        dw      1500h, STR15, Disp_15
        dw      1600h, STR16, Disp_16
        dw      1700h, STR17, Disp_17
        dw      1800h, STRUN, Disp_Str
        dw      1900h, STR19, Disp_Str
        dw      1a00h, STR1a, Disp_1a
        dw      1b00h, STR1b, Disp_Str
        dw      1c00h, STR1c, Disp_1c
        dw      1d00h, STRUN, Disp_Str
        dw      1e00h, STRUN, Disp_Str
        dw      1f00h, STRUN, Disp_Str
        dw      2000h, STRUN, Disp_Str
        dw      2100h, STR21, Disp_21
        dw      2200h, STR22, Disp_22
        dw      2300h, STR23, Disp_23
        dw      2400h, STR24, Disp_24
        dw      2500h, STR25, Disp_25
        dw      2600h, STR26, Disp_26
        dw      2700h, STR27, Disp_27
        dw      2800h, STR28, Disp_28
        dw      2900h, STR29, Disp_29
        dw      2a00h, STR2a, Disp_Str
        dw      2b00h, STR2b, Disp_2b
        dw      2c00h, STR2c, Disp_Str
        dw      2d00h, STR2d, Disp_2d
        dw      2e00h, STR2e, Disp_2e
        dw      2f00h, STR2f, Disp_Str
        dw      3000h, STR30, Disp_Str
        dw      3100h, STR31, Disp_Str
        dw      3200h, STRUN, Disp_Str
        dw      3300h, STR33, Disp_33
        dw      3400h, STRUN, Disp_Str
        dw      3500h, STR35, Disp_35
        dw      3600h, STR36, Disp_36
        dw      3700h, STR37, Disp_Str
        dw      3800h, STR38, Disp_Str
        dw      3900h, STR39, Disp_39
        dw      3a00h, STR3a, Disp_3a
        dw      3b00h, STR3b, Disp_3b
        dw      3c00h, STR3c, Disp_3c
        dw      3d00h, STR3d, Disp_3d
        dw      3e00h, STR3e, Disp_3e
        dw      3f00h, STR3f, Disp_3f
        dw      4000h, STR40, Disp_40
        dw      4100h, STR41, Disp_41
        dw      4200h, STR42, Disp_42
        dw      4300h, STR43, Disp_43
        dw      4400h, STR44, Disp_44
        dw      4500h, STR45, Disp_45
        dw      4600h, STR46, Disp_46
        dw      4700h, STR47, Disp_47
        dw      4800h, STR48, Disp_48
        dw      4900h, STR49, Disp_49
        dw      4a00h, STR4a, Disp_4a
        dw      4b00h, STR4b, Disp_4b
        dw      4c00h, STR4c, Disp_4c
        dw      4d00h, STR4d, Disp_Str
        dw      4e00h, STR4e, Disp_4e
        dw      4f00h, STR4f, Disp_Str
        dw      5000h, STRUN, Disp_Str
        dw      5100h, STRUN, Disp_Str
        dw      5200h, STRUN, Disp_Str
        dw      5300h, STRUN, Disp_Str
        dw      5400h, STR54, Disp_Str
        dw      5500h, STRUN, Disp_Str
        dw      5600h, STR56, Disp_56
        dw      5700h, STR57, Disp_57
        dw      5800h, STRUN, Disp_Str
        dw      5900h, STR59, Disp_Str
        dw      5a00h, STR5a, Disp_5a
        dw      5b00h, STR5b, Disp_5b
        dw      5c00h, STR5c, Disp_5c
        dw      5d00h, STRUN, Disp_Str
        dw      5e00h, STRUN, Disp_Str
        dw      5f00h, STRUN, Disp_Str
        dw      6000h, STRUN, Disp_Str
        dw      6100h, STRUN, Disp_Str
        dw      6200h, STR62, Disp_Str
LENFC   EQU     $ - FCtbl

;
; The XX's are just place holders for help in alignment during debugging
;
STR00   db      'Terminate Program'
        db      0

STR01   db      'Keyboard Input With Echo'
        db      0

STR02   db      'Output Character  Hex XX  ASCII X'
        db      0

STR03   db      'Serial Input'
        db      0

STR04   db      'Serial Output     Hex XX  ASCII X'
        db      0

STR05   db      'Printer Output    Hex XX  ASCII X'
        db      0

STR06   db      'Direct Console I/O - '
        db      0

STR06I  db      'Input Character'
        db      0

STR07   db      'Direct Console Input Without Echo'
        db      0

STR08   db      'Console Input Without Echo'
        db      0

STR09   db      'Display String -->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR0a   db      'Buffered Keyboard Input To XXXX:XXXXH'
        db      0

STR0b   db      'Check Standard Input Status'
        db      0

STR0c   db      'Clear Keyboard and Do Function XXH'
        db      0

STR0d   db      'Reset Disk'
        db      0

STR0e   db      'Select Disk XXH'
        db      0

STR0f   db      'Open File Using FCB at XXXX:XXXXH'
        db      0

STR10   db      'Close File Using FCB at XXXX:XXXXH'
        db      0

STR11   db      'Search For First Matching File Using FCB at XXXX:XXXXH'
        db      0

STR12   db      'Search For Next Matching File Using FCB at XXXX:XXXXH'
        db      0

STR13   db      'Delete File Using FCB at XXXX:XXXXH'
        db      0

STR14   db      'Read Sequential File Record Using FCB at XXXX:XXXXH'
        db      0

STR15   db      'Write Sequential File Record Using FCB at XXXX:XXXXH'
        db      0

STR16   db      'Create File Using FCB at XXXX:XXXXH'
        db      0

STR17   db      'Rename File Using FCB at XXXX:XXXXH'
        db      0

STR19   db      'Report Current Drive'
        db      0

STR1a   db      'Set Disk Transfer Address To XXXX:XXXXH'
        db      0

STR1b   db      'Get FAT Information For Default Drive'
        db      0

STR1c   db      'Get FAT Information For Drive XXH'
        db      0

STR21   db      'Read Random File Record Using FCB at XXXX:XXXXH'
        db      0

STR22   db      'Write Random File Record Using FCB at XXXX:XXXXH'
        db      0

STR23   db      'Get File Size Using FCB at XXXX:XXXXH'
        db      0

STR24   db      'Set Random Record Field Using FCB at XXXX:XXXXH'
        db      0

STR25   db      'Set Interrupt Vector XXH to XXXX:XXXXH'
        db      0

STR26   db      'Create New Program Segment At Segment XXXXH'
        db      0

STR27   db      'Read XXXXH Random File Records Using FCB at XXXX:XXXXH'
        db      0

STR28   db      'Write XXXXH Random File Records Using FCB at XXXX:XXXXH'
        db      0

STR29   db      'Parse Filename -->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR2a   db      'Get Date'
        db      0

STR2b   db      'Set Date To mm/dd/yy  XX/XX/XX'
        db      0

STR2c   db      'Get Time'
        db      0

STR2d   db      'Set Time To Hrs:Mins:Secs:Hunds  XX:XX:XX:XX'
        db      0

STR2e   db      'Set Disk Write Verification XXX'
        db      0

STR2f   db      'Get Disk Transfer Address'
        db      0

STR30   db      'Get DOS Version Number'
        db      0

STR31   db      'Terminate Process and Remain Resident'
        db      0

STR33   db      'Get/Set Control-Break Status'
        db      0

STR33G  db      'Get Control-Break Status'
        db      0

STR33S  db      'Set Control-Break Status XXX'
        db      0

STR35   db      'Get Interrupt Vector XXH'
        db      0

STR36   db      'Get Disk Free Space On Drive XXH'
        db      0

STR37   db      'Get DOS Switch Character'
        db      0

STR38   db      'Get/Set Country Dependent Information'
        db      0

STR39   db      'Create Subdir --->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR3a   db      'Remove Subdir --->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR3b   db      'Change Dir To --->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR3c   db      'Create File ----->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR3d   db      'Open File ------->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR3e   db      'Close File Handle XXXXH'
        db      0

STR3f   db      'Read XXXXH Bytes From File or Device XXXXH'
        db      0

STR40   db      'Write XXXXH Bytes To File or Device XXXXH'
        db      0

STR41   db      'Delete File ----->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR42   db      'Move File Handle XXXXH Pointer By XXXX:XXXXH From '
        db      'XXXXXXXXXXXXXXXXX'
        db      0

STR43   db      'Get/Set File Attributes'
        db      0

STR43G  db      'Get File Attrib ->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR43S  db      'Set File Attrib ->XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR44   db      'I/O Control For Devices'
        db      0

STR440  db      'Get Info For Device XXXXH'
        db      0

STR441  db      'Set Info For Device XXXXH to XXXXH'
        db      0

STR442  db      'Read XXXXH Bytes From Drive Control Channel of File XXXXH'
        db      0

STR443  db      'Write XXXXH Bytes To Drive Control Channel of File XXXXH'
        db      0

STR444  db      'Read XXXXH Bytes From Control Channel of Drive XXH'
        db      0

STR445  db      'Write XXXXH Bytes To Control Channel of Drive XXH'
        db      0

STR446  db      'Get Input Status of Device XXXXH'
        db      0

STR447  db      'Get Output Status of Device XXXXH'
        db      0

STR448  db      'Report Whether Device XXXXH Has Removable Media'
        db      0

STR4411 db      'Set Retries For Device XXXXH to XXXXH With Interval of XXXXH'
        db      0

STR45   db      'Duplicate File Handle XXXXH'
        db      0

STR46   db      'Force Duplication of Handle XXXXH to XXXXH'
        db      0

STR47   db      'Get Current Directory of Drive XXH into XXXX:XXXXH'
        db      0

STR48   db      'Allocate XXXXH Paragraphs of Memory'
        db      0

STR49   db      'Free Allocated Memory at Segment XXXXH'
        db      0

STR4a   db      'Modify Memory Block at Segment XXXXH to be XXXXH Paragraphs'
        db      0

STR4b   db      'Load or Execute Program ---->XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR4c   db      'Terminate Process With Return Code XXH'
        db      0

STR4d   db      'Get Return Code of Subprocess'
        db      0

STR4e   db      'Find First Matching File --->XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR4f   db      'Find Next Matching File'
        db      0

STR54   db      'Get Verify State'
        db      0

STR56   db      'Rename File   Old Name ----->XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR56N  db      '              New Name ----->XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXX'
        db      0

STR57   db      'Get/Set Date and Time of File Handle XXXXH'
        db      0

STR57G  db      'Get Date and Time of File Handle XXXXH'
        db      0

STR57S  db      'Set Date and Time of File Handle XXXXH'
        db      0

STR59   db      'Get Extended Error Code'
        db      0

STR5a   db      'Create Temp File  XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR5b   db      'Create New File   XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
        db      'XXXXXXXXXXXL'
        db      0

STR5c   db      'Lock/Unlock File XXXXH'
        db      0

STR5c0  db      'Lock File XXXXH'
        db      0

STR5c1  db      'Unlock File XXXXH'
        db      0

STR62   db      'Get PSP Address'
        db      0

STRUN   db      '** Undocumented Function Code **'
        db      0

;
; Don't change the size of the following strings
;
Blanks3  db      '   '
Blanks17 db      '                 '
ONstr    db      'ON '
OFFstr   db      'OFF'
BOFstr   db      'Beginning of File'
CURstr   db      'Current Location '
EOFstr   db      'End of File      '


Open_Window:
        push    ES
        mov     BX,OFFSET W1        ; window parameters
;
; Save current contents of window area
;
        mov     SI,[BX].startmem    ; screen addr of start of window
        mov     DX,[BX].height
        mov     ES,Winseg           ; point to allocated memory block
        mov     DI,0000
saverow:
        push    DS
        mov     CX,[BX].xwidth
        mov     DS,Scrseg           ; get screen segment
        push    SI                  ; save screen offset
rep     movsw                       ; do word to get char and attribute
        pop     SI
        pop     DS
        add     SI,BytesPL          ; next row down
        dec     DX
        jnz     saverow
;
; Draw window
;
        mov     ES,Scrseg           ; get screen segment
        mov     DI,[BX].startmem    ; physical addr of start of window
        mov     AH,HIWHITE
;
; Draw top border
;
        push    DI
        mov     AL,ULC              ; write upper left corner
        stosw
        mov     CX,[BX].xwidth
        sub     CX,2
        mov     AL,BRDROW
rep     stosw
        mov     AL,URC              ; write upper right corner
        stosw
        pop     DI
        add     DI,BytesPL          ; next row down
;
; Draw middle of window
;
        mov     DX,[BX].height
        sub     DX,2
winrows:
        push    DI
        mov     AL,BRDCOL           ; left border column
        stosw
        mov     CX,[BX].xwidth
        sub     CX,2
        mov     AL,BLANK
rep     stosw
        mov     AL,BRDCOL           ; right border column
        stosw
        pop     DI
        add     DI,BytesPL          ; next row down
        dec     DX
        jnz     winrows
;
; Draw bottom border
;
        push    DI
        mov     AL,LLC              ; write lower left corner
        stosw
        mov     CX,[BX].xwidth
        sub     CX,2
        mov     AL,BRDROW
rep     stosw
        mov     AL,LRC              ; write lower right corner
        stosw
        pop     DI
        pop     ES
        ret


Close_Window:
        mov     BX,OFFSET W1
        mov     DI,[BX].startmem    ; physical addr of screen area
        mov     ES,Scrseg           ; point to allocated memory block
        mov     SI,0000             ; start of save memory block
        mov     DX,[BX].height
resrow:
        push    DS
        mov     CX,[BX].xwidth
        mov     DS,Winseg           ; get saved memory segment
        push    DI                  ; save screen offset
rep     movsw                       ; do word to get char and attribute
        pop     DI
        pop     DS
        add     DI,BytesPL          ; next row down
        dec     DX
        jnz     resrow
        ret

;
; Print a string in window.
; Entry:
;        CX = Row, Col position relative to start of window
;        BX = Window pointer
;        AH = Attribute
;        DX = addr of string
;
WPrint:
        push    ES
        call    GetRC               ; convert to row, col in DI
        mov     ES,Scrseg
        mov     SI,DX               ; move string address
wpwrt:
        cmp     BYTE PTR [SI],00    ; test for string terminator <NULL>
        jz      wpexit
        lodsb
        stosw
        jmp     wpwrt
wpexit:
        pop     ES
        ret

;
; Write one character and attribute to window
;
; Entry:
;        CX = Row, Col position relative to start of window
;        BX = Window pointer
;        AH = attr
;        AL = char
;
WChar:
        push    ES
        call    GetRC               ; convert to row, col in DI
        mov     ES,Scrseg
        stosw
        pop     ES
        ret

;
; Convert row, col in CX to physical addr in DI
;
GetRC:
        push    AX
        push    DX
        mov     DI,[BX].startmem    ; physical start of window memory
        add     DI,BytesPL          ; go down a row
        add     DI,2                ; go in one char, this is 0,0
        mov     AL,CH
        xor     AH,AH               ; AX = relative row number
        mul     BytesPL             ; this clobbers DX
        add     DI,AX
        mov     AX,CX               ; restore coordinates
        xor     AH,AH               ; AX = relative col number
        shl     AX,1                ; times 2 for attribute
        add     DI,AX
        pop     DX
        pop     AX
        ret

;
; WRITE HEX WORD
; Convert a hex word to an ASCII string and display it
; Entry:
;        CX = Row, Col position relative to start of window
;        BX = Window pointer
;        AX = Word to convert
;
Whexwd:
        push    AX
        push    BX
        push    CX
        push    DX
;
        push    BX                  ; save window pointer
        push    CX                  ;  and row, col
        mov     DI,OFFSET Astr
        xchg    AH,AL
        call    Shexbyt
        xchg    AH,AL
        call    Shexbyt
        xor     AL,AL
        stosb                       ; make sure of terminating NULL
        mov     DX,OFFSET Astr
        pop     CX                  ; get row, col
        pop     BX                  ;  and Window ptr
        mov     AH,HIWHITE          ; set attribute
        call    WPrint
;
        pop     DX
        pop     CX
        pop     BX
        pop     AX
        ret

;
; STORE HEX WORD
; Convert a hex word to ASCII and store it in destination string
; Entry:
;        AX = Word to convert
;        DI = destination pointer
;
Shexwrd:
        xchg    AL,AH               ; convert upper half first
        call    Shexbyt
        xchg    AL,AH               ; convert lower half
        call    Shexbyt
        ret

;
; STORE HEX BYTE
; Convert a hex byte to ASCII and store it in destination string
; Entry:
;        AL = Byte to convert
;        DI = destination pointer
;
Shexbyt:
        push    AX
        mov     AH,AL               ; save temporarily
        shr     AL,1
        shr     AL,1
        shr     AL,1
        shr     AL,1
        cmp     AL,10
        jb      wh1
        add     AL,07
wh1:
        add     AL,'0'
        stosb
        mov     AL,AH
        and     AL,0fh
        cmp     AL,10
        jb      wh2
        add     AL,07
wh2:
        add     AL,'0'
        stosb
        pop     AX
        ret

;
; Check if key pressed requires special handling
;
; Entry:
;      AX = key pressed
;
Disp_Key:
        mov     DI,OFFSET Keytbl    ; keys and subroutine addresses
        mov     CX,LENKTAB / 4      ; number of entries
cmpdk:
        cmp     AX,[DI]             ; is key in table?
        jz      dkexec
        add     DI,4                ; no, point to next key value
        loop    cmpdk
        ret
dkexec:
        add     DI,2
        call    [WORD PTR DI]
        ret

;
; Table of keys to watch for followed by the address of the routine to execute
;
Keytbl  dw      ESCAPE,  DO_Esc
        dw      BIGS,    Do_Skey
        dw      SMALLS,  Do_Skey
        dw      BIGR,    Do_Rkey
        dw      SMALLR,  Do_Rkey
LENKTAB EQU     $ - Keytbl

;
; If ESC key, clear 'running flag' so Int 21h will not be stopped each time
;
Do_Esc:
        mov     AL,00
        mov     Run_Flg,AL
        ret

;
; 'S' key - skip successive functions of current type.
; Return to intercepting calls when something new comes along.
; This is so you don't have to sit through dozens if Function '2' calls
; while the target program outputs a string to the display.
;
Do_Skey:
        mov     AL,0ffh
        mov     Skip_Flg,AL         ; set flag to show we should skip something
        mov     AX,AXsave           ; get current function code
        mov     Skip_Typ,AH         ; save it
        ret

;
; 'R' key - stop after INT 21h call and let user see result registers
;
Do_Rkey:
        mov     AL,0ffh
        mov     Ret_Flg,AL          ; set flag
        ret

;
; Wait for any key pressed
;
Get_Key:
        mov     AH,00
        int     16h
        ret

XTest:
        mov     AH,02               ; write char
        mov     DL,07               ; <BELL>
        int     21h
        iret

;
; Define format of WINDOW structure
;
Window  STRUC
   leftrow   dw     ?
   leftcol   dw     ?
   rightrow  dw     ?
   rightcol  dw     ?
   xwidth    dw     ?
   height    dw     ?
   startmem  dw     ?
Window  ENDS

;
; Allocate and intialize WINDOW parameters
;
W1       Window     <8, 2, 18, 74, 0, 0, 0>

Winseg    dw     0000                ; store segment of allocated memory
                                     ;  for saving screen data
Scrseg    dw     0b800h              ; segment where screen memory can be found
BytesPL   dw     80*2                ; number of bytes per line (char + attr)
Run_Flg   db     0ffh                ; 'running' flag
Ret_Flg   db     00                  ; 'stop on return' flag
;
; The following two variables are initialized the way they are to skip
; the first Int 21 call generated by 'STEPDOS' to EXEC the target program.
;
Skip_Typ db     4bh                 ; type of function call to skip temporarily
Skip_Flg db     0ffh                ; set if function should be skipped

Save21   dw     ?                   ; save original Int21 vector here, IP
         dw     ?                   ;  and SEG

Ssave    LABEL  DWORD
SPsave   dw     ?                   ; save some of the user's registers here
SSsave   dw     ?                   ;  others will be on local stack

AXsave   dw     ?                   ; these will have been left on user's
DSsave   dw     ?                   ;  stack instead of local stack
CSsave   dw     ?
IPsave   dw     ?
FLsave   dw     ?
;
; Parameter block that will be passed to the EXEC function call (4bh) of DOS
;
Param_Block     LABEL  WORD
SegEnv   dw     ?                   ; segment addr of environment string
SegCmd   dw     ?                   ; segmented ptr to command line
         dw     ?
FCBptr1  dw     ?                   ; segmented ptr to first FCB
         dw     ?
FCBptr2  dw     ?                   ; segmented ptr to second FCB
         dw     ?

;
; File name that will be passed to the EXEC function call of DOS
;
Filename db     128 dup (0)
FNsize   dw     0
;
; Command line from PSP:80h will be copied to here work from
;
PSPstr   db     128 dup (0)

;
; Command Line that will be passed to the EXEC function call of DOS
;
CLstr    db     128 dup (0)

;
; Two FCB's that will be passed to the EXEC function call of DOS
;
FCB1     db     0
         db     11 dup (' ')
         db     0, 0, 0, 0

FCB2     db     0
         db     11 dup (' ')
         db     0, 0, 0, 0

COMstr  db      '.COM'
EXEstr  db      '.EXE'
;
INITmsg  db     'STEPDOS Version 1.0'
         db     CR
         db     LF
         db     '$'

Memerr   db     CR
         db     LF
         db     'Error Allocating Window Memory$'

Execmsg  db     CR
         db     LF
         db     'Unable to execute target program$'

Findmsg  db     CR
         db     LF
         db     'Unable to find target program$'

Umsg     db     CR
         db     LF
         db     'Usage: STEPDOS <filename>$'

RegStr1  db     ' AX   BX   CX   DX   DI   SI   BP   SP'
         db     '   DS   ES   SS   CS   IP   FL'
         db     0

RegStr2  db     '---- ---- ---- ---- ---- ---- ---- ----'
         db     ' ---- ---- ---- ---- ---- ----'
         db     0

HlpStr1  db     'kip Current Function'
         db     0

HlpStr2  db     'eturn Code'
         db     0

HlpStr3  db     ' - Non Stop'
         db     0

HlpStr4  db     'Press Any Key To Continue'
         db     0

Astr     db     32 dup (0)          ; string for converting ASCII characters

;
; Local Program Stack Area
;
         db     128 dup (?)
Pstack   EQU    $

;
; Target Stack Area
;
         db     128 dup (?)
Tstack   EQU    $


IF TESTING

Istr     db     128 dup (' ')

Ostr     db     'Output String'
         db     0
ENDIF


IF TESTING
        cli
        mov     AX,0
        mov     ES,AX
        mov     AX,OFFSET XTest
        mov     ES:[INT21OFF],AX
        mov     ES:[INT21OFF+2],CS
        sti
ENDIF

IF TESTING
        include test.asm
        jmp     execdn
ELSE
        int     21h
ENDIF

Code    ENDS

        END     Main