|
Table of Content | Chapter Twenty (Part 5) |
|
Table of Content | Chapter Twenty (Part 5) |
| CHAPTER TWENTY: THE PC KEYBOARD (Part 4) |
| 20.5 - The Keyboard Interrupt Service Routine |
| 20.5 The Keyboard Interrupt Service Routine |
The int 16h ISR is the interface between application programs and the keyboard. In a similar vein, the int 9 ISR is the interface between the keyboard hardware and the int 16h ISR. It is the job of the int 9 ISR to process keyboard hardware interrupts, convert incoming scan codes to scan/ASCII code combinations and place them in the typeahead buffer, and process other messages the keyboard generates.
To convert keyboard scan codes to scan/ASCII codes, the int
9 ISR must keep track of the current state of the modifier keys. When a scan code comes
along, the int 9 ISR can use the xlat instruction to translate the scan code
to an ASCII code using a table int 9 selects on the basis of the modifier flags. Another
important issue is that the int 9 handler must handle special key sequences like
ctrl-alt-del (reset) and PrtSc. The following assembly code provides a simple int 9
handler for the keyboard. It does not support alt-Keypad ASCII code entry or a few other
minor features, but it does support almost everything you need for a keyboard interrupt
service routine. Certainly it demonstrates all the techniques you need to know when
programming the keyboard.
; INT9.ASM
;
; A short TSR to provide a driver for the keyboard hardware interrupt.
;
; 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'
OldInt9 dword ?
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
NumLockScan equ 45h
ScrlLockScan equ 46h
CapsLockScan equ 3ah
CtrlScan equ 1dh
AltScan equ 38h
RShiftScan equ 36h
LShiftScan equ 2ah
InsScanCode equ 52h
DelScanCode equ 53h
; Bits for the various modifier keys
RShfBit equ 1
LShfBit equ 2
CtrlBit equ 4
AltBit equ 8
SLBit equ 10h
NLBit equ 20h
CLBit equ 40h
InsBit equ 80h
KbdFlags equ <byte ptr ds:[17h]>
KbdFlags2 equ <byte ptr ds:[18h]>
KbdFlags3 equ <byte ptr ds:[96h]>
KbdFlags4 equ <byte ptr ds:[97h]>
byp equ <byte ptr>
cseg segment para public 'code'
assume ds:nothing
; Scan code translation table.
; The incoming scan code from the keyboard selects a row.
; The modifier status selects the column.
; The word at the intersection of the two is the scan/ASCII code to
; put into the PC's type ahead buffer.
; If the value fetched from the table is zero, then we do not put the
; character into the type ahead buffer.
;
; norm shft ctrl alt num caps shcap shnum
ScanXlat word 0000h, 0000h, 0000h, 0000h, 0000h, 0000h, 0000h, 0000h
word 011bh, 011bh, 011bh, 011bh, 011bh, 011bh, 011bh, 011bh ;ESC
word 0231h, 0231h, 0000h, 7800h, 0231h, 0231h, 0231h, 0321h ;1 !
word 0332h, 0340h, 0300h, 7900h, 0332h, 0332h, 0332h, 0332h ;2 @
word 0433h, 0423h, 0000h, 7a00h, 0433h, 0433h, 0423h, 0423h ;3 #
word 0534h, 0524h, 0000h, 7b00h, 0534h, 0534h, 0524h, 0524h ;4 $
word 0635h, 0625h, 0000h, 7c00h, 0635h, 0635h, 0625h, 0625h ;5 %
word 0736h, 075eh, 071eh, 7d00h, 0736h, 0736h, 075eh, 075eh ;6 ^
word 0837h, 0826h, 0000h, 7e00h, 0837h, 0837h, 0826h, 0826h ;7 &
word 0938h, 092ah, 0000h, 7f00h, 0938h, 0938h, 092ah, 092ah ;8 *
word 0a39h, 0a28h, 0000h, 8000h, 0a39h, 0a39h, 0a28h, 0a28h ;9 (
word 0b30h, 0b29h, 0000h, 8100h, 0b30h, 0b30h, 0b29h, 0b29h ;0 )
word 0c2dh, 0c5fh, 0000h, 8200h, 0c2dh, 0c2dh, 0c5fh, 0c5fh ;- _
word 0d3dh, 0d2bh, 0000h, 8300h, 0d3dh, 0d3dh, 0d2bh, 0d2bh ;= +
word 0e08h, 0e08h, 0e7fh, 0000h, 0e08h, 0e08h, 0e08h, 0e08h ;bksp
word 0f09h, 0f00h, 0000h, 0000h, 0f09h, 0f09h, 0f00h, 0f00h ;Tab
; norm shft ctrl alt num caps shcap shnum
word 1071h, 1051h, 1011h, 1000h, 1071h, 1051h, 1051h, 1071h ;Q
word 1177h, 1057h, 1017h, 1100h, 1077h, 1057h, 1057h, 1077h ;W
word 1265h, 1245h, 1205h, 1200h, 1265h, 1245h, 1245h, 1265h ;E
word 1372h, 1352h, 1312h, 1300h, 1272h, 1252h, 1252h, 1272h ;R
word 1474h, 1454h, 1414h, 1400h, 1474h, 1454h, 1454h, 1474h ;T
word 1579h, 1559h, 1519h, 1500h, 1579h, 1559h, 1579h, 1559h ;Y
word 1675h, 1655h, 1615h, 1600h, 1675h, 1655h, 1675h, 1655h ;U
word 1769h, 1749h, 1709h, 1700h, 1769h, 1749h, 1769h, 1749h ;I
word 186fh, 184fh, 180fh, 1800h, 186fh, 184fh, 186fh, 184fh ;O
word 1970h, 1950h, 1910h, 1900h, 1970h, 1950h, 1970h, 1950h ;P
word 1a5bh, 1a7bh, 1a1bh, 0000h, 1a5bh, 1a5bh, 1a7bh, 1a7bh ;[ {
word 1b5dh, 1b7dh, 1b1dh, 0000h, 1b5dh, 1b5dh, 1b7dh, 1b7dh ;] }
word 1c0dh, 1c0dh, 1c0ah, 0000h, 1c0dh, 1c0dh, 1c0ah, 1c0ah ;enter
word 1d00h, 1d00h, 1d00h, 1d00h, 1d00h, 1d00h, 1d00h, 1d00h ;ctrl
word 1e61h, 1e41h, 1e01h, 1e00h, 1e61h, 1e41h, 1e61h, 1e41h ;A
word 1f73h, 1f5eh, 1f13h, 1f00h, 1f73h, 1f53h, 1f73h, 1f53h ;S
; norm shft ctrl alt num caps shcap shnum
word 2064h, 2044h, 2004h, 2000h, 2064h, 2044h, 2064h, 2044h ;D
word 2166h, 2146h, 2106h, 2100h, 2166h, 2146h, 2166h, 2146h ;F
word 2267h, 2247h, 2207h, 2200h, 2267h, 2247h, 2267h, 2247h ;G
word 2368h, 2348h, 2308h, 2300h, 2368h, 2348h, 2368h, 2348h ;H
word 246ah, 244ah, 240ah, 2400h, 246ah, 244ah, 246ah, 244ah ;J
word 256bh, 254bh, 250bh, 2500h, 256bh, 254bh, 256bh, 254bh ;K
word 266ch, 264ch, 260ch, 2600h, 266ch, 264ch, 266ch, 264ch ;L
word 273bh, 273ah, 0000h, 0000h, 273bh, 273bh, 273ah, 273ah ;; :
word 2827h, 2822h, 0000h, 0000h, 2827h, 2827h, 2822h, 2822h ;' "
word 2960h, 297eh, 0000h, 0000h, 2960h, 2960h, 297eh, 297eh ;` ~
word 2a00h, 2a00h, 2a00h, 2a00h, 2a00h, 2a00h, 2a00h, 2a00h ;LShf
word 2b5ch, 2b7ch, 2b1ch, 0000h, 2b5ch, 2b5ch, 2b7ch, 2b7ch ;\ |
word 2c7ah, 2c5ah, 2c1ah, 2c00h, 2c7ah, 2c5ah, 2c7ah, 2c5ah ;Z
word 2d78h, 2d58h, 2d18h, 2d00h, 2d78h, 2d58h, 2d78h, 2d58h ;X
word 2e63h, 2e43h, 2e03h, 2e00h, 2e63h, 2e43h, 2e63h, 2e43h ;C
word 2f76h, 2f56h, 2f16h, 2f00h, 2f76h, 2f56h, 2f76h, 2f56h ;V
; norm shft ctrl alt num caps shcap shnum
word 3062h, 3042h, 3002h, 3000h, 3062h, 3042h, 3062h, 3042h ;B
word 316eh, 314eh, 310eh, 3100h, 316eh, 314eh, 316eh, 314eh ;N
word 326dh, 324dh, 320dh, 3200h, 326dh, 324dh, 326dh, 324dh ;M
word 332ch, 333ch, 0000h, 0000h, 332ch, 332ch, 333ch, 333ch ;, <
word 342eh, 343eh, 0000h, 0000h, 342eh, 342eh, 343eh, 343eh ;. >
word 352fh, 353fh, 0000h, 0000h, 352fh, 352fh, 353fh, 353fh ;/ ?
word 3600h, 3600h, 3600h, 3600h, 3600h, 3600h, 3600h, 3600h ;rshf
word 372ah, 0000h, 3710h, 0000h, 372ah, 372ah, 0000h, 0000h ;* PS
word 3800h, 3800h, 3800h, 3800h, 3800h, 3800h, 3800h, 3800h ;alt
word 3920h, 3920h, 3920h, 0000h, 3920h, 3920h, 3920h, 3920h ;spc
word 3a00h, 3a00h, 3a00h, 3a00h, 3a00h, 3a00h, 3a00h, 3a00h ;caps
word 3b00h, 5400h, 5e00h, 6800h, 3b00h, 3b00h, 5400h, 5400h ;F1
word 3c00h, 5500h, 5f00h, 6900h, 3c00h, 3c00h, 5500h, 5500h ;F2
word 3d00h, 5600h, 6000h, 6a00h, 3d00h, 3d00h, 5600h, 5600h ;F3
word 3e00h, 5700h, 6100h, 6b00h, 3e00h, 3e00h, 5700h, 5700h ;F4
word 3f00h, 5800h, 6200h, 6c00h, 3f00h, 3f00h, 5800h, 5800h ;F5
; norm shft ctrl alt num caps shcap shnum
word 4000h, 5900h, 6300h, 6d00h, 4000h, 4000h, 5900h, 5900h ;F6
word 4100h, 5a00h, 6400h, 6e00h, 4100h, 4100h, 5a00h, 5a00h ;F7
word 4200h, 5b00h, 6500h, 6f00h, 4200h, 4200h, 5b00h, 5b00h ;F8
word 4300h, 5c00h, 6600h, 7000h, 4300h, 4300h, 5c00h, 5c00h ;F9
word 4400h, 5d00h, 6700h, 7100h, 4400h, 4400h, 5d00h, 5d00h ;F10
word 4500h, 4500h, 4500h, 4500h, 4500h, 4500h, 4500h, 4500h ;num
word 4600h, 4600h, 4600h, 4600h, 4600h, 4600h, 4600h, 4600h ;scrl
word 4700h, 4737h, 7700h, 0000h, 4737h, 4700h, 4737h, 4700h ;home
word 4800h, 4838h, 0000h, 0000h, 4838h, 4800h, 4838h, 4800h ;up
word 4900h, 4939h, 8400h, 0000h, 4939h, 4900h, 4939h, 4900h ;pgup
word 4a2dh, 4a2dh, 0000h, 0000h, 4a2dh, 4a2dh, 4a2dh, 4a2dh ;-
word 4b00h, 4b34h, 7300h, 0000h, 4b34h, 4b00h, 4b34h, 4b00h ;left
word 4c00h, 4c35h, 0000h, 0000h, 4c35h, 4c00h, 4c35h, 4c00h ;Center
word 4d00h, 4d36h, 7400h, 0000h, 4d36h, 4d00h, 4d36h, 4d00h ;right
word 4e2bh, 4e2bh, 0000h, 0000h, 4e2bh, 4e2bh, 4e2bh, 4e2bh ;+
word 4f00h, 4f31h, 7500h, 0000h, 4f31h, 4f00h, 4f31h, 4f00h ;end
; norm shft ctrl alt num caps shcap shnum
word 5000h, 5032h, 0000h, 0000h, 5032h, 5000h, 5032h, 5000h ;down
word 5100h, 5133h, 7600h, 0000h, 5133h, 5100h, 5133h, 5100h ;pgdn
word 5200h, 5230h, 0000h, 0000h, 5230h, 5200h, 5230h, 5200h ;ins
word 5300h, 532eh, 0000h, 0000h, 532eh, 5300h, 532eh, 5300h ;del
word 0,0,0,0,0,0,0,0 ; --
word 0,0,0,0,0,0,0,0 ; --
word 0,0,0,0,0,0,0,0 ; --
word 5700h, 0000h, 0000h, 0000h, 5700h, 5700h, 0000h, 0000h ;F11
word 5800h, 0000h, 0000h, 0000h, 5800h, 5800h, 0000h, 0000h ;F12
;****************************************************************************
;
; AL contains keyboard scan code.
PutInBuffer proc near
push ds
push bx
mov bx, 40h ;Point ES at the BIOS
mov ds, bx ; variables.
; If the current scan code is E0 or E1, we need to take note of this fact
; so that we can properly process cursor keys.
cmp al, 0e0h
jne TryE1
or KbdFlags3, 10b ;Set E0 flag
and KbdFlags3, 0FEh ;Clear E1 flag
jmp Done
TryE1: cmp al, 0e1h
jne DoScan
or KbdFlags3, 1 ;Set E1 flag
and KbdFlags3, 0FDh ;Clear E0 Flag
jmp Done
; Before doing anything else, see if this is Ctrl-Alt-Del:
DoScan: cmp al, DelScanCode
jnz TryIns
mov bl, KbdFlags
and bl, AltBit or CtrlBit ;Alt = bit 3, ctrl = bit 2
cmp bl, AltBit or CtrlBit
jne DoPIB
mov word ptr ds:[72h], 1234h ;Warm boot flag.
jmp dword ptr cs:RebootAdrs ;REBOOT Computer
RebootAdrs dword 0ffff0000h ;Reset address.
; Check for the INS key here. This one needs to toggle the ins bit
; in the keyboard flags variables.
TryIns: cmp al, InsScanCode
jne TryInsUp
or KbdFlags2, InsBit ;Note INS is down.
jmp doPIB ;Pass on INS key.
TryInsUp: cmp al, InsScanCode+80h ;INS up scan code.
jne TryLShiftDn
and KbdFlags2, not InsBit ;Note INS is up.
xor KbdFlags, InsBit ;Toggle INS bit.
jmp QuitPIB
; Handle the left and right shift keys down here.
TryLShiftDn: cmp al, LShiftScan
jne TryLShiftUp
or KbdFlags, LShfBit ;Note that the left
jmp QuitPIB ; shift key is down.
TryLShiftUp: cmp al, LShiftScan+80h
jne TryRShiftDn
and KbdFlags, not LShfBit ;Note that the left
jmp QuitPIB ; shift key is up.
TryRShiftDn: cmp al, RShiftScan
jne TryRShiftUp
or KbdFlags, RShfBit ;Right shf is down.
jmp QuitPIB
TryRShiftUp: cmp al, RShiftScan+80h
jne TryAltDn
and KbdFlags, not RShfBit ;Right shf is up.
jmp QuitPIB
; Handle the ALT key down here.
TryAltDn: cmp al, AltScan
jne TryAltUp
or KbdFlags, AltBit ;Alt key is down.
GotoQPIB: jmp QuitPIB
TryAltUp: cmp al, AltScan+80h
jne TryCtrlDn
and KbdFlags, not AltBit ;Alt key is up.
jmp DoPIB
; Deal with the control key down here.
TryCtrlDn: cmp al, CtrlScan
jne TryCtrlUp
or KbdFlags, CtrlBit ;Ctrl key is down.
jmp QuitPIB
TryCtrlUp: cmp al, CtrlScan+80h
jne TryCapsDn
and KbdFlags, not CtrlBit ;Ctrl key is up.
jmp QuitPIB
; Deal with the CapsLock key down here.
TryCapsDn: cmp al, CapsLockScan
jne TryCapsUp
or KbdFlags2, CLBit ;Capslock is down.
xor KbdFlags, CLBit ;Toggle capslock.
jmp QuitPIB
TryCapsUp: cmp al, CapsLockScan+80h
jne TrySLDn
and KbdFlags2, not CLBit ;Capslock is up.
call SetLEDs
jmp QuitPIB
; Deal with the Scroll Lock key down here.
TrySLDn: cmp al, ScrlLockScan
jne TrySLUp
or KbdFlags2, SLBit ;Scrl lock is down.
xor KbdFlags, SLBit ;Toggle scrl lock.
jmp QuitPIB
TrySLUp: cmp al, ScrlLockScan+80h
jne TryNLDn
and KbdFlags2, not SLBit ;Scrl lock is up.
call SetLEDs
jmp QuitPIB
; Handle the NumLock key down here.
TryNLDn: cmp al, NumLockScan
jne TryNLUp
or KbdFlags2, NLBit ;Numlock is down.
xor KbdFlags, NLBit ;Toggle numlock.
jmp QuitPIB
TryNLUp: cmp al, NumLockScan+80h
jne DoPIB
and KbdFlags2, not NLBit ;Numlock is up.
call SetLEDs
jmp QuitPIB
; Handle all the other keys here:
DoPIB: test al, 80h ;Ignore other up keys.
jnz QuitPIB
; If the H.O. bit is set at this point, we'd best only have a zero in AL.
; Otherwise, this is an up code which we can safely ignore.
call Convert
test ax, ax ;Chk for bad code.
je QuitPIB
PutCharInBuf: push cx
mov cx, ax
mov ah, 5 ;Store scan code into
int 16h ; type ahead buffer.
pop cx
QuitPIB: and KbdFlags3, 0FCh ;E0, E1 not last code.
Done: pop bx
pop ds
ret
PutInBuffer endp
;****************************************************************************
;
; Convert- AL contains a PC Scan code. Convert it to an ASCII char/Scan
; code pair and return the result in AX. This code assumes
; that DS points at the BIOS variable space (40h).
Convert proc near
push bx
test al, 80h ;See if up code
jz DownScanCode
mov ah, al
mov al, 0
jmp CSDone
; Okay, we've got a down key. But before going on, let's see if we've
; got an ALT-Keypad sequence.
DownScanCode: mov bh, 0
mov bl, al
shl bx, 1 ;Multiply by eight to compute
shl bx, 1 ; row index index the scan
shl bx, 1 ; code xlat table
; Compute modifier index as follows:
;
; if alt then modifier = 3
test KbdFlags, AltBit
je NotAlt
add bl, 3
jmp DoConvert
; if ctrl, then modifier = 2
NotAlt: test KbdFlags, CtrlBit
je NotCtrl
add bl, 2
jmp DoConvert
; Regardless of the shift setting, we've got to deal with numlock
; and capslock. Numlock is only a concern if the scan code is greater
; than or equal to 47h. Capslock is only a concern if the scan code
; is less than this.
NotCtrl: cmp al, 47h
jb DoCapsLk
test KbdFlags, NLBit ;Test Numlock bit
je NoNumLck
test KbdFlags, LShfBit or RShfBit ;Check l/r shift.
je NumOnly
add bl, 7 ;Numlock and shift.
jmp DoConvert
NumOnly: add bl, 4 ;Numlock only.
jmp DoConvert
; If numlock is not active, see if a shift key is:
NoNumLck: test KbdFlags, LShfBit or RShfBit ;Check l/r shift.
je DoConvert ;normal if no shift.
add bl, 1
jmp DoConvert
; If the scan code's value is below 47h, we need to check for capslock.
DoCapsLk: test KbdFlags, CLBit ;Chk capslock bit
je DoShift
test KbdFlags, LShfBit or RShfBit ;Chk for l/r shift
je CapsOnly
add bl, 6 ;Shift and capslock.
jmp DoConvert
CapsOnly: add bl, 5 ;Capslock
jmp DoConvert
; Well, nothing else is active, check for just a shift key.
DoShift: test KbdFlags, LShfBit or RShfBit ;l/r shift.
je DoConvert
add bl, 1 ;Shift
DoConvert: shl bx, 1 ;Word array
mov ax, ScanXlat[bx]
CSDone: pop bx
ret
Convert endp
; SetCmd- Sends the command byte in the AL register to the 8042
; keyboard microcontroller chip (command register at
; port 64h).
SetCmd proc near
push cx
push ax ;Save command value.
cli ;Critical region, no ints now.
; Wait until the 8042 is done processing the current command.
xor cx, cx ;Allow 65,536 times thru loop.
Wait4Empty: in al, 64h ;Read keyboard status register.
test al, 10b ;Input buffer full?
loopnz Wait4Empty ;If so, wait until empty.
; Okay, send the command to the 8042:
pop ax ;Retrieve command.
out 64h, al
sti ;Okay, ints can happen again.
pop cx
ret
SetCmd endp
; SendCmd- The following routine sends a command or data byte to the
; keyboard data port (port 60h).
SendCmd proc near
push ds
push bx
push cx
mov cx, 40h
mov ds, cx
mov bx, ax ;Save data byte
mov bh, 3 ;Retry cnt.
RetryLp: cli ;Disable ints while accessing HW.
; Clear the Error, Acknowledge received, and resend received flags
; in KbdFlags4
and byte ptr KbdFlags4, 4fh
; Wait until the 8042 is done processing the current command.
xor cx, cx ;Allow 65,536 times thru loop.
Wait4Empty: in al, 64h ;Read keyboard status register.
test al, 10b ;Input buffer full?
loopnz Wait4Empty ;If so, wait until empty.
; Okay, send the data to port 60h
mov al, bl
out 60h, al
sti ;Allow interrupts now.
; Wait for the arrival of an acknowledgement from the keyboard ISR:
xor cx, cx ;Wait a long time, if need be.
Wait4Ack: test byp KbdFlags4,10h ;Acknowledge received bit.
jnz GotAck
loop Wait4Ack
dec bh ;Do a retry on this guy.
jne RetryLp
; If the operation failed after 3 retries, set the error bit and quit.
or byp KbdFlags4,80h ;Set error bit.
GotAck: pop cx
pop bx
pop ds
ret
SendCmd endp
; SetLEDs- Updates the KbdFlags4 LED bits from the KbdFlags
; variable and then transmits new flag settings to
; the keyboard.
SetLEDs proc near
push ax
push cx
mov al, KbdFlags
mov cl, 4
shr al, cl
and al, 111b
and KbdFlags4, 0F8h ;Clear LED bits.
or KbdFlags4, al ;Mask in new bits.
mov ah, al ;Save LED bits.
mov al, 0ADh ;Disable kbd for now.
call SetCmd
mov al, 0EDh ;8042 set LEDs cmd.
call SendCmd ;Send the command to 8042.
mov al, ah ;Get parameter byte
call SendCmd ;Send parameter to the 8042.
mov al, 0AEh ;Reenable keyboard.
call SetCmd
mov al, 0F4h ;Restart kbd scanning.
call SendCmd
pop cx
pop ax
ret
SetLEDs endp
; MyInt9- Interrupt service routine for the keyboard hardware
; interrupt.
MyInt9 proc far
push ds
push ax
push cx
mov ax, 40h
mov ds, ax
mov al, 0ADh ;Disable keyboard
call SetCmd
cli ;Disable interrupts.
xor cx, cx
Wait4Data: in al, 64h ;Read kbd status port.
test al, 10b ;Data in buffer?
loopz Wait4Data ;Wait until data available.
in al, 60h ;Get keyboard data.
cmp al, 0EEh ;Echo response?
je QuitInt9
cmp al, 0FAh ;Acknowledge?
jne NotAck
or KbdFlags4, 10h ;Set ack bit.
jmp QuitInt9
NotAck: cmp al, 0FEh ;Resend command?
jne NotResend
or KbdFlags4, 20h ;Set resend bit.
jmp QuitInt9
; Note: other keyboard controller commands all have their H.O. bit set
; and the PutInBuffer routine will ignore them.
NotResend: call PutInBuffer ;Put in type ahead buffer.
QuitInt9: mov al, 0AEh ;Reenable the keyboard
call SetCmd
mov al, 20h ;Send EOI (end of interrupt)
out 20h, al ; to the 8259A PIC.
pop cx
pop ax
pop ds
iret
MyInt9 endp
Main proc
assume ds:cseg
mov ax, cseg
mov ds, ax
print
byte "INT 9 Replacement",cr,lf
byte "Installing....",cr,lf,0
; Patch into the INT 9 interrupt vector. Note that the
; statements above have made cseg the current data segment,
; so we can store the old INT 9 value directly into
; the OldInt9 variable.
cli ;Turn off interrupts!
mov ax, 0
mov es, ax
mov ax, es:[9*4]
mov word ptr OldInt9, ax
mov ax, es:[9*4 + 2]
mov word ptr OldInt9+2, ax
mov es:[9*4], offset MyInt9
mov es:[9*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 db 16 dup (?)
zzzzzzseg ends
end Main
|
Table of Content | Chapter Twenty (Part 5) |
Chapter Twenty: The PC Keyboard (Part
4)
29 SEP 1996