Reverse Code Engineering RCE CD +sandman 2000/ReverseCodeEngineeringRceCdsandman2000.iso/RCE/Library/Manuels & Misc/Assembly/AOA.ZIP/CH21/INT17.ASM

Assembly Source File | 1994-07-25 | 10.8 KB | 377 lines

; INT17.ASM
;
; A short passive TSR that replaces the BIOS' int 17h handler.
; This routine demonstrates the function of each of the int 17h
; functions that a standard BIOS would provide.
;
; Note that this code does not patch into int 2Fh (multiplex interrupt)
; nor can you remove this code from memory except by rebooting.
; If you want to be able to do these two things (as well as check for
; a previous installation), see the chapter on resident programs.  Such
; code was omitted from this program because of length constraints.
;
;
; cseg and EndResident must occur before the standard library segments!

cseg        segment    para public 'code'
cseg        ends

; Marker segment, to find the end of the resident section.

EndResident    segment    para public 'Resident'
EndResident    ends

        .xlist
        include     stdlib.a
        includelib    stdlib.lib
        .list


byp        equ    <byte ptr>

cseg        segment    para public 'code'
        assume    cs:cseg, ds:cseg

OldInt17    dword    ?


; BIOS variables:

PrtrBase    equ    8
PrtrTimeOut    equ    78h




; This code handles the INT 17H operation.  INT 17H is the BIOS routine
; to send data to the printer and report on the printer's status.  There
; are three different calls to this routine, depending on the contents
; of the AH register.  The DX register contains the printer port number.
;
; DX=0 -- Use LPT1:
; DX=1 -- Use LPT2:
; DX=2 -- Use LPT3:
; DX=3 -- Use LPT4:
;
; AH=0 -- Print the character in AL to the printer.  Printer status is
;      returned in AH.  If bit #0 = 1 then a timeout error occurred.
;
; AH=1 -- Initialize printer.  Status is returned in AH.
;
; AH=2 -- Return printer status in AH.
;
;
; The status bits returned in AH are as follows:
;
;  Bit    Function            Non-error values
;  ---   --------------------------     ----------------
;   0     1=time out error            0
;   1       unused                x
;   2       unused                x
;   3     1=I/O error                0
;   4     1=selected, 0=deselected.        1
;   5     1=out of paper            0
;   6     1=acknowledge                x
;   7     1=not busy                x
;
; Note that the hardware returns bit 3 with zero if an error has occurred,
; with one if there is no error.  The software normally inverts this bit
; before returning it to the caller.
;
;
; Printer port hardware locations:
;
; There are three ports used by the printer hardware:
;
; PrtrPortAdrs   ---  Output port where data is sent to printer (8 bits).
; PrtrPortAdrs+1 ---  Input port where printer status can be read (8 bits).
; PrtrPortAdrs+2 ---  Output port where control information is sent to the
;              printer.
;
; Data output port- 8-bit data is transmitted to the printer via this port.
;
; Input status port:
;            bit 0: unused.
;            bit 1: unused.
;            bit 2: unused.
;
;            bit 3: -Error, normally this bit means that the
;                printer has encountered an error.  However,
;                with the P101 installed this is a data
;                return line for the keyboard scan.
;
;            bit 4: +SLCT, normally this bit is used to determine
;                if the printer is selected or not.  With the
;                P101 installed this is a data return
;                line for the keyboard scan.
;
;            bit 5: +PE, a 1 in this bit location means that the
;                printer has detected the end of paper.  On
;                many printer ports, this bit has been found
;                to be inoperative.
;
;            bit 6: -ACK, A zero in this bit position means that
;                the printer has accepted the last character
;                and is ready to accept another.  This bit
;                is not normally used by the BIOS as bit 7
;                also provides this function (and more).
;
;            bit 7: -Busy, When this signal is active (0) the
;                printer is busy and cannot accept data.
;                When this bit is set to one, the printer
;                can accept another character.
;
;
;
; Output control port:
;
;             Bit 0: +Strobe, A 0.5 us (minimum) active high pulse
;                on this bit clocks the data latched into the
;                printer data output port to the printer.
;
;            Bit 1: +Auto FD XT - A 1 stored at this bit causes
;                the printer to line feed after a line is
;                printed.  On some printer interfaces (e.g.,
;                the Hercules Graphics Card) this bit is
;                inoperative.
;
;            Bit 2: -INIT, a zero on this bit (for a minimum of
;                50 us) will cause the printer to (re)init-
;                ialize itself.
;
;            Bit 3: +SLCT IN, a one in this bit selects the
;                printer.  A zero will cause the printer to
;                go off-line.
;
;            Bit 4: +IRQ ENABLE, a one in this bit position
;                allows an interrupt to occur when -ACK
;                changes from one to zero.
;
;            Bit 5: Direction control on BI-DIR port. 0=output,
;                   1=input.
;            Bit 6: reserved, must be zero.
;            Bit 7: reserved, must be zero.

MyInt17        proc    far
        assume    ds:nothing

        push    ds
        push    bx
        push    cx
        push    dx

        mov    bx, 40h            ;Point DS at BIOS vars.
        mov    ds, bx

        cmp    dx, 3            ;Must be LPT1..LPT4.
        ja    InvalidPrtr

        cmp    ah, 0        ;Branch to the appropriate code for
        jz    PrtChar        ; the printer function
        cmp    ah, 2
        jb    PrtrInit
        je    PrtrStatus

; If they passed us an opcode we don't know about, just return.

InvalidPrtr:    jmp    ISR17Done



; Initialize the printer by pulsing the init line for at least 50 us.
; The delay loop below will delay well beyond 50 usec even on the fastest
; machines.

PrtrInit:    mov    bx, dx            ;Get printer port value.
        shl    bx, 1            ;Convert to byte index.
        mov    dx, PrtrBase[bx]    ;Get printer base address.
        test    dx, dx            ;Does this printer exist?
        je    InvalidPrtr        ;Quit if no such printer.
        add    dx, 2            ;Point dx at control reg.
        in    al, dx            ;Read current status.
        and    al, 11011011b        ;Clear INIT/BIDIR bits.
        out    dx, al            ;Reset printer.
        mov    cx, 0            ;This will produce at least
PIDelay:    loop    PIDelay            ; a 50 usec delay.
        or    al, 100b        ;Stop resetting printer.
        out    dx, al
        jmp    ISR17Done


; Return the current printer status.  This code reads the printer status
; port and formats the bits for return to the calling code.

PrtrStatus:    mov    bx, dx            ;Get printer port value.
        shl    bx, 1            ;Convert to byte index.
        mov    dx, PrtrBase[bx]    ;Base address of printer port.
        mov    al, 00101001b        ;Dflt: every possible error.
        test    dx, dx            ;Does this printer exist?
        je    InvalidPrtr        ;Quit if no such printer.
        inc    dx            ;Point at status port.
        in    al, dx            ;Read status port.
        and    al, 11111000b        ;Clear unused/timeout bits.
        jmp    ISR17Done



; Print the character in the accumulator!

PrtChar:        mov    bx, dx
        mov    cl, PrtrTimeOut[bx]    ;Get time out value.
        shl    bx, 1            ;Convert to byte index.
        mov    dx, PrtrBase[bx]    ;Get Printer port address
        or    dx, dx            ;Non-nil pointer?
        jz    NoPrtr2            ; Branch if a nil ptr

; The following code checks to see if an acknowlege was received from
; the printer.  If this code waits too long, a time-out error is returned.
; Acknowlege is supplied in bit #7 of the printer status port (which is
; the next address after the printer data port).

        push    ax
        inc    dx            ;Point at status port
        mov    bl, cl            ;Put timeout value in bl
        mov    bh, cl            ; and bh.
WaitLp1:    xor    cx, cx            ;Init count to 65536.
WaitLp2:    in    al, dx            ;Read status port
        mov    ah, al            ;Save status for now.
        test    al, 80h            ;Printer acknowledge?
        jnz    GotAck            ;Branch if acknowledge.
        loop    WaitLp2            ;Repeat 65536 times.
        dec    bl            ;Decrement time out value.
        jnz    WaitLp1            ;Repeat 65536*TimeOut times.

; See if the user has selected no timeout:

        cmp     bh, 0
        je    WaitLp1

; TIMEOUT ERROR HAS OCCURRED!
;
; A timeout - I/O error is returned to the system at this point.
; Either we fall through to this point from above (time out error) or
; the referenced printer port doesn't exist.  In any case, return an error.

NoPrtr2:    or    ah, 9            ;Set timeout-I/O error flags
        and    ah, 0F9h        ;Turn off unused flags.
        xor    ah, 40h            ;Flip busy bit.

; Okay, restore registers and return to caller.

        pop    cx            ;Remove old ax.
        mov    al, cl            ;Restore old al.
        jmp    ISR17Done


; If the printer port exists and we've received an acknowlege, then it's
; okay to transmit data to the printer.  That job is handled down here.

GotAck:        mov    cx, 16            ;Short delay if crazy prtr
GALp:        loop    GALp            ; needs hold time after ack.
        pop    ax            ;Get char to output and
        push    ax            ; save again.
        dec    dx            ;Point DX at printer port.
        pushf                ;Turn off interrupts for now.
        cli
        out    dx, al            ;Output data to the printer.

; The following short delay gives the data time to travel through the
; parallel lines.  This makes sure the data arrives at the printer before
; the strobe (the times can vary depending upon the capacitance of the
; parallel cable's lines).

        mov    cx, 16            ;Give data time to settle
DataSettleLp:    loop    DataSettleLp        ; before sending strobe.

; Now that the data has been latched on the printer data output port, a
; strobe must be sent to the printer.  The strobe line is connected to
; bit zero of the printer port.  Also note that this clears bit 5 of the
; control port.  This ensures that the port continues to operate as an
; output port if it is a bidirectional device.  This code also clears bits
; six and seven which IBM claims should be left zero.

        inc    dx            ;Point DX at the printer
        inc    dx            ; control output port.
        in    al, dx            ;Get current control bits.
        and    al, 01eh        ;Force strobe line to zero and
        out    dx, al            ; make sure it's an output port.


        mov    cx, 16            ;Short delay to allow data
Delay0:        loop    Delay0            ; to become good.

        or    al, 1            ;Send out the (+) strobe.
        out    dx, al            ;Output (+) strobe to bit 0

        mov    cx, 16            ;Short delay to lengthen strobe
StrobeDelay:    loop    StrobeDelay

        and    al, 0FEh        ;Clear the strobe bit.
        out    dx, al            ;Output to control port.
        popf                ;Restore interrupts.

        pop    dx            ;Get old AX value
        mov    al, dl            ;Restore old AL value

ISR17Done:    pop    dx
        pop    cx
        pop    bx
        pop    ds
        iret
MyInt17        endp





Main        proc

        mov    ax, cseg
        mov    ds, ax

        print
        byte    "INT 17h Replacement",cr,lf
        byte    "Installing....",cr,lf,0

; Patch into the INT 17 interrupt vector.  Note that the
; statements above have made cseg the current data segment,
; so we can store the old INT 17 value directly into
; the OldInt17 variable.

        cli                ;Turn off interrupts!
        mov    ax, 0
        mov    es, ax
        mov    ax, es:[17h*4]
        mov    word ptr OldInt17, ax
        mov    ax, es:[17h*4 + 2]
        mov    word ptr OldInt17+2, ax
        mov    es:[17h*4], offset MyInt17
        mov    es:[17h*4+2], cs
        sti                ;Okay, ints back on.


; We're hooked up, the only thing that remains is to terminate and
; stay resident.

        print
        byte    "Installed.",cr,lf,0

        mov    ah, 62h            ;Get this program's PSP
        int    21h            ; value.

        mov    dx, EndResident        ;Compute size of program.
        sub    dx, bx
        mov    ax, 3100h        ;DOS TSR command.
        int    21h
Main        endp
cseg        ends

sseg        segment    para stack 'stack'
stk        byte    1024 dup ("stack   ")
sseg        ends

zzzzzzseg    segment    para public 'zzzzzz'
LastBytes    byte    16 dup (?)
zzzzzzseg    ends
        end    Main