Liren Large Software Subsidy 10/10.iso/l/l440/2.ddi/CHAP7/MON.ASM

Assembly Source File | 1990-09-27 | 8.9 KB | 417 lines

    page    78,132
    title    Monitor for IBM PC by Tim Paterson

    include    dos.inc

;System equates

BreakVect    =    1BH
TermAddr    equ    word ptr 0AH
PROMPT        =    ">"

ExecBlock    struc

Environment    dw    0        ;Pass on parent's environment
CommandTail    dw    80H
CommandTailSeg    dw    0
FCB1        dw    5CH
FCB1Seg        dw    0
FCB2        dw    6CH
FCB2Seg        dw    0
InitSp        dw    0
InitSs        dw    0
InitIp        dw    0
InitCs        dw    0

ExecBlock    ends

    .model    small
    .code
    .data
Strings    segment    byte public
Strings    ends
InitSeg segment public
InitSeg ends
LastSeg    segment byte
    ret                ;End of init code
LastSeg    ends

DGroup    group    _TEXT,_DATA,Strings,InitSeg,LastSeg

    .data

    public    AxSave,BxSave,SpSave,SsSave,DsSave,CsSave,IpSave,FlSave
    public    BpSave,SiSave,DiSave,TestPSP

    extrn    LineBuf:byte, TCount:word

ExecFile    ExecBlock<,DGroup:LineBuf>
TestPSP        dw    0
NextInt15    dd    0

    ALIGN    2
    dw    80H dup(?)        ;Working stack area
STACK    label    word
;Register save area
AxSave    dw    ?
BxSave    dw    ?
CxSave    dw    ?
DxSave    dw    ?
SpSave    dw    ?
BpSave    dw    ?
SiSave    dw    ?
DiSave    dw    ?
DsSave    dw    ?
EsSave    dw    ?
SsSave    dw    ?
CsSave    dw    ?
IpSave    dw    ?
FlSave    dw    ?

;Start of Monitor code

    .code
    assume    cs:DGroup,ds:DGroup,es:DGroup,ss:DGroup

    public    Monitor, Command, Error, PrintAbort, PErr, ErrMes

    extrn    InBuf:near, OutCh:near, CrLf:near, PrintMes:near, ScanB:near
    extrn    Tab:near, ReEnter:near

    org    100H

Monitor:
         cld

    IFDEF    DEBUG
;Copy psp
    xor    si,si
    mov    di,si
    push    cs
    pop    es
    mov    cx,100H/2
rep    movsw
    push    cs
    pop    ds
    push    cs
    pop    ss
    ENDIF    ;DEBUG

    mov    sp,offset DGroup:Stack
    DOS    Version,0
    cmp    al,3            ;Version OK?
    jae    VersionOK
;Bad version.  Terminate in a DOS 1.0-compatible way
    DOS    Print,,<offset DGroup:BadVersionMsg>
    int    20H

VersionOK:
    call    Init
    mov    si,offset DGroup:Header
    call    PrintMes
;Load file for debugging
    mov    ax,cs

    IFDEF    DEBUG
    sub    ax,10H            ;Get to true PSP
    mov    es,ax
    ENDIF    ;DEBUG

    mov    bx,[CsSave]        ;First segment to free
    sub    bx,ax            ;Compute paragraphs we're keeping
    DOS    ResizeMem

    IFDEF    DEBUG
    push    cs
    pop    es
    ENDIF    ;DEBUG

    mov    si,80H            ;Point to command line in PSP
    lodsb                ;Get length byte
    cbw
    xchg    cx,ax            ;Put length in cx
    call    ParseFile
    mov    si,dx
    cmp    byte ptr [si],0        ;Was there a file name?
    jz    Command
    mov    [AxSave],ax
    mov    [ExecFile].CommandTailSeg,ds
    mov    [ExecFile].FCB1Seg,ds
    mov    [ExecFile].FCB2Seg,ds
    mov    bx,offset DGroup:ExecFile
    DOS    Exec,1            ;Load, don't execute
    jc    NoFileLoad
    mov    ax,[ExecFile].InitIp
    mov    [IpSave],ax
    mov    ax,[ExecFile].InitCs
    mov    [CsSave],ax
    mov    ax,[ExecFile].InitSp
    mov    [SpSave],ax
    mov    ax,[ExecFile].InitSs
    mov    [SsSave],ax
    DOS    GetPSP
    mov    [DsSave],bx        ;DS = ES = PSP
    mov    [EsSave],bx
    mov    es,bx
    mov    es:[TermAddr],offset DGroup:ProgTerminate
    mov    es:[TermAddr+2],cs    ;Terminate address now set
    mov    [TestPSP],bx
    mov    bx,cs

    IFDEF    DEBUG
    sub    bx,10H            ;True PSP
    ENDIF    ;DEBUG

    DOS    SetPSP            ;Change back to our own PSP
Command:
;Re-establish initial conditions
    cld
    mov    ax,cs
    mov    ds,ax
    mov    es,ax
    mov    ss,ax
    mov    sp,offset DGroup:STACK
    sti
    MOV    AL,PROMPT
    CALL    OutCh
    CALL    INBUF        ;Get command line
;From now and throughout command line processing, SI points
;to next character in command line to be processed.
    CALL    SCANB        ;Scan off leading blanks
    JZ    COMMAND        ;Null command?
    LODSB            ;AL=first non-blank character
;Prepare command letter for table lookup
    SUB    AL,"B"        ;Low end range check
    JC    ERR1
    CMP    AL,"U"+1-"B"    ;Upper end range check
    JNC    ERR1
    SHL    AL,1        ;Times two
    CBW            ;Now a 16-bit quantity
    XCHG    BX,AX        ;In BX we can address with it
    CALL    [BX+COMTAB]    ;Execute command
    jmp    Command        ;Get next command

NoFileLoad:
    mov    si,offset DGroup:FileErrMsg
    jmp    PrintAbort

ERR1:    JMP    PERR

BadVersionMsg    db    "Invalid DOS--version 3 or later required$"
Header        db    13,10,"IBM-PC Monitor 1.0",13,10+80H
SYNERR        db    '^'
ERRMES        db    " Error",13,10+80H
ProgEndMsg    db    13,10,"Program terminated",13,10+80H
FileErrMsg    db    "Error loading file",13,10+80H

;Ctrl-BREAK handler.  Allows program abort.
Interrupt:
    MOV    AL,20H        ;End of interrupt command
    OUT    20H,al        ;Send to 8259A
    mov    al,0AEH        ;Enable keyboard
    out    64H,al        ;Send to keyboard
    MOV    AL,"^"
    CALL    OutCh
    MOV    AL,"C"
    CALL    OutCh
    call    CRLF
    jmp    Command

SysReq:
    cmp    ax,8500H        ;Sys Req key pressed?
    jnz    ChainInt15
    mov    cs:[TCount],1        ;Stop step mode
    jmp    ReEnter

ChainInt15:
    jmp    cs:[NextInt15]

;Command Table. Command letter indexes into table to get
;address of command. PERR prints error for no such command.

DwExt    Macro    lab
    extrn    lab:near
    dw    offset DGroup:lab
    EndM

COMTAB    label    word
    DW    PERR        ;B
    DwExt    COMPARE        ;C
    DwExt    DUMP        ;D
    DwExt    ENTER        ;E
    DwExt    FILL        ;F
    DwExt    GO        ;G
    DW    PERR        ;H
    DwExt    INPUT        ;I
    DW    PERR        ;J
    DW    PERR        ;K
    DW    PERR        ;L
    DwExt    MOVE        ;M
    DW    PERR        ;N
    DwExt    OUTPUT        ;O
    DW    PERR        ;P
    DW    Quit        ;Q
    DwExt    REG        ;R
    DwExt    SEARCH        ;S
    DwExt    TRACE        ;T
    DwExt    UnAssemble    ;U

ParseFile:
;Find start and end of file name
;Inputs:
;    ds:si = pointer to input string
;    cx = length of string
;Outputs:
;    ax = Starting value for ax (drive validity flags)
;    dx = File name to execute, zero-terminated

    mov    bx,si            ;Save initial pointer
    call    ScanB
    mov    dx,si            ;Save starting address
    call    FindNameEnd
    sub    bx,si
    neg    bx            ;Amount scanned so far
    sub    cx,bx            ;Amount remaining in string
    mov    bx,si            ;Save end of name--start of args
    mov    di,offset DGroup:LineBuf+1
    mov    [di-1],cl        ;Put length in first byte
    inc    cx            ;Copy terminating CR
rep    movsb                ;Copy to argument buffer
    mov    si,bx            ;Restore start of args
    mov    di,5CH            ;First FCB
    DOS    ParseName,1        ;Parse file name, scan off blanks
    cbw                ;0FFH if invalid drive
    and    al,ah            ;Make sure al is zero or one
    xchg    cx,ax            ;Save return value in cl
    call    FindNameEnd        ;Skip over any "\" chars
    mov    di,6CH            ;Second FCB
    DOS    ParseName,1        ;Parse file name, scan off blanks
    cbw                ;0FFH if invalid drive
    and    ah,al            ;Make sure ah is zero or one
    mov    al,cl
    mov    byte ptr [bx],0        ;Zero terminate file name
    ret

FindNameEnd:
    lodsb
    cmp    al," "            ;Check for blank or control char
    jbe    NameEnd
    cmp    al,","
    jz    NameEnd
    cmp    al,";"
    jz    NameEnd
    cmp    al,"/"
    jnz    FindNameEnd
NameEnd:
    dec    si            ;Point back at terminator
    ret


;Command error. SI has been incremented beyond the
;command letter so it must decremented for the
;error pointer to work.

PERR:
    DEC    SI

;Syntax error. SI points to character in the input buffer
;which caused error. By subtracting from start of buffer,
;we will know how far to tab over to appear directly below
;it on the terminal. Then print "^ Error".

ERROR:
    SUB    SI,offset DGroup:LINEBUF-1    ;How many char processed so far?
    MOV    CX,SI        ;Parameter for TAB in CX
    CALL    TAB        ;Directly below bad char
    MOV    SI,offset DGroup:SYNERR    ;Error message

;Print error message and abort to command level

PrintAbort:
    CALL    PRINTMES
    JMP    COMMAND

;************************************************************
; "Q" - Quit

ProgTerminate:
;TestPSP = our own PSP if we are terminating the child in order to quit
;Monitor (suppress "program terminated" message).
    push    cs
    pop    ds
    mov    bx,cs

    IFDEF    DEBUG
    sub    bx,10H            ;True PSP
    ENDIF    ;DEBUG

    mov    ax,bx
    xchg    bx,[TestPSP]        ;Set to our own PSP to show no child
    cmp    ax,bx            ;Do we have a child?
    jz    JustExit
    mov    si,offset DGroup:ProgEndMsg
    jmp    PrintAbort        ;Print message, get next command line

Quit:
;We must end child first.  If no child, TestPSP = our own PSP, so we'll
;just terminate directly.  If there is a child, set TestPSP to our own PSP
;as a flag to ProgTerminate to suppress "program terminated" message.
    mov    bx,cs

    IFDEF    DEBUG
    sub    bx,10H            ;True PSP
    ENDIF    ;DEBUG

    xchg    bx,[TestPSP]
    DOS    SetPSP
JustExit:
    lds    dx,[NextInt15]
    DOS    SetVect,15H
    mov    ax,76*100H + 0        ;Terminate, no error
    int    21H

;************************************************************
;
;Initialization code
;
;Each module can have its own initialization code.  The module simply
;puts the code in InitSeg.  All InitSegs are combined end-to-end,
;thus executing the init code for each module.  The RET instruction in
;LastSeg, immediately following InitSeg, returns program flow back to
;the caller of Init.
;
;All this code is thrown away when memory is resized.

InitSeg    segment
    assume    cs:DGroup,ds:Dgroup

Init:
;one-time register initialization
    DOS    SetVect,BreakVect,<offset DGroup:Interrupt>
    DOS    GetVect,15H
    mov    word ptr [NextInt15],bx
    mov    word ptr [NextInt15+2],es
    push    ds
    pop    es
    DOS    SetVect,15H,<offset DGroup:SysReq>
    mov    [TestPSP],cs        ;Use our own PSP until program loads
    xor    ax,ax
    mov    di,offset DGroup:AxSave
    mov    cx,8            ;Init all general registers
rep    stosw
    mov    ax,cs
    mov    bx,offset DGroup:InitSeg
    mov    cl,4
    shr    bx,cl
    add    ax,bx
rep    stosw                ;Fill 4 segment registers
    mov    ax,100H
    stosw                ;Set IP
    mov    ah,2
    stosw                ;Enable user interrupts
    mov    byte ptr [SpSave+1],1    ;Set user SP to 100H
;Will now fall into next module's init code
InitSeg    ends

    END    Monitor