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Annotation of os2sdk/demos/examples/iopl/ioplsub.asm, revision 1.1

1.1     ! root        1:        TITLE    CURSOR
        !             2: 
        !             3: ;      This file exports the function _GetCurLoc which gets the location
        !             4: ;      of the cursor on the CRT screen.
        !             5: ;
        !             6: ;      This routine illustrates the use of the DosPortAccess() call.  This
        !             7: ;      call is supposed to give the IOPL segment access to ports and CLI/STI
        !             8: ;      instructions. In fact, on the PC/AT (80286) there is no enforcement.
        !             9: ;      This call is provided for future compatibility with the 80386.
        !            10: ;      At present, the use of DosPortAccess() from an IOPL segment is not
        !            11: ;      supported (the calls are commented out here) but will be in the future.
        !            12: ;      The form and placement of these calls is indicated here as a guide
        !            13: ;      to future usage.
        !            14: ;
        !            15: ;      One thing to beware of: if you disable interrupts (CLI) they may be
        !            16: ;      re-enabled for you by the operating system.  This will occur if you
        !            17: ;      generate a fault of some sort.  The easiest example is a segment not
        !            18: ;      present fault.  When the segment is loaded and your code starts to
        !            19: ;      execute the interrupts will be enabled.  The solution is simple: don't
        !            20: ;      load any selectors within the CLI/STI code.
        !            21: ;
        !            22: ;      Any other fault will cause your process to be booted (i.e. GP fault).
        !            23: ;
        !            24:        .286p
        !            25: 
        !            26: _TEXT2 SEGMENT  BYTE PUBLIC 'CODE'
        !            27: _TEXT2 ENDS
        !            28: _DATA  SEGMENT  WORD PUBLIC 'DATA'
        !            29: _DATA  ENDS
        !            30: CONST  SEGMENT  WORD PUBLIC 'CONST'
        !            31: CONST  ENDS
        !            32: _BSS   SEGMENT  WORD PUBLIC 'BSS'
        !            33: _BSS   ENDS
        !            34: 
        !            35: DGROUP GROUP   CONST,  _BSS,   _DATA
        !            36: 
        !            37: ;       EXTRN   DOSPORTACCESS:FAR
        !            38: 
        !            39:        ASSUME  CS: _TEXT2, DS: DGROUP, SS: DGROUP, ES: DGROUP
        !            40: 
        !            41: _TEXT2    SEGMENT
        !            42: 
        !            43:        PORT1           EQU     3D4h
        !            44:        PORT2           EQU     3D5h
        !            45:        CURSOR_H        EQU     14      ; cursor location HIGH register
        !            46:        CURSOR_L        EQU     15      ; cursor location LOW register
        !            47:        ACCESSREQ       EQU     0       ; request access to port(s)
        !            48:        ACCESSREL       EQU     1       ; release access to port(s)
        !            49: 
        !            50: ;**    _GetCurLoc - gets cursor location on the CRT screen
        !            51: ;
        !            52: ;      ENTRY   NONE
        !            53: ;
        !            54: ;      EXIT    (AX) = cursor location
        !            55: ;
        !            56: ;      USES    AX, BX, DX
        !            57: 
        !            58:        PUBLIC  _GetCurLoc              ; gets cursor location on CRT screen
        !            59: 
        !            60: _GetCurLoc     PROC    FAR
        !            61: 
        !            62: ;       push    0               ; RESERVED WORD
        !            63: ;       push    ACCESSREQ       ; request access to port(s)
        !            64: ;       push    PORT1
        !            65: ;       push    PORT2
        !            66: ;       call    DOSPORTACCESS   ; request access to ports PORT1, PORT2
        !            67: 
        !            68:        mov     ax,CURSOR_H     ; address of register we want to read from
        !            69:        call    ReadLoc         ; gets cursor location (H) in AL
        !            70:        mov     bh,al           ; (BH) = cursor location (H)
        !            71: 
        !            72:        mov     ax,CURSOR_L     ; address of register we want to read from
        !            73:        call    ReadLoc         ; gets cursor location (L) in AL
        !            74:        mov     ah,bh           ; (AH) = cursor location (H)
        !            75: 
        !            76:        push    ax              ; save cursor location
        !            77: ;       push    0               ; RESERVED WORD
        !            78: ;       push    ACCESSREL       ; release access to port(s)
        !            79: ;       push    PORT1
        !            80: ;       push    PORT2
        !            81: ;       call    DOSPORTACCESS   ; release access to ports PORT1, PORT2
        !            82:        pop     ax              ; restore cursor location
        !            83: 
        !            84:        ret
        !            85: _GetCurLoc     ENDP
        !            86: 
        !            87: ;*     ReadLoc - reads cursor location on the CRT screen
        !            88: ;
        !            89: ;      ENTRY   (AX) = address of register to read from
        !            90: ;
        !            91: ;      EXIT    (AL) = cursor location read
        !            92: ;
        !            93: ;      USES    AX,DX
        !            94: 
        !            95: ReadLoc        PROC    NEAR
        !            96:        cli
        !            97:        mov     dx,PORT1        ; set address we want to output to
        !            98:        out     dx,al
        !            99:        jmp     $+2             ; PC/AT IO delay
        !           100:        mov     dx,PORT2        ; set address we want to read from
        !           101:        in      al,dx           ; read cursor location
        !           102:        sti
        !           103:        ret
        !           104: ReadLoc        ENDP
        !           105: 
        !           106: _TEXT2 ENDS
        !           107: 
        !           108: END

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