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NOBRK.ASM
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Assembly Source File
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1988-04-04
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7KB
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322 lines
name BRK
page 55,132
title 'CTRL-BRK and CTRL-C disble and enable controller'
COMMENT @
COPYRIGHT (c) John Pulliam, Walter Cox, Benjamin J. Diss
October 15, 1987, April 4, 1988
This is a simple device driver that disables the Ctrl-C and
Ctrl-Break interrupts. It may be toggled on or off by sending the word 'on'
or the word 'off' to the driver. The driver is installed with the name
'ctrl-brk'.
ex.
copy con ctrl-brk
off
^Z
1 file(s) copied
To assist in communicating with the driver a utility called nobrk is included.
It will send the command tail to the driver called 'ctrl-brk'.
The driver operates by intercepting all keystokes and looking for ctrl-brk
and ctrl-c. If active it will intercept them, it not active it passes the
keystokes to the appropriate handler.
This program is provided "AS IS" and the authors assume NO LIABILITY
for damages from the use of this program.
For DOS 2.0 +.
@
code segment public 'CODE'
driver proc far
assume cs:code,ds:code,es:code
org 0
ctrl equ 04h ; Ctrl Key is Depressed
seg40 equ 40h ; Keyboard buffer segment
kbflag equ 17h ; Offset of KBFLAG in SEG 40H
kbinctl equ 60h ; Keyboard IN port address
kbcmdp equ 61h ; Keyboard COMMAND port address
init_cmd equ 0
read_cmd equ 4
write_cmd equ 8
cr equ 0dh
lf equ 0ah
eom equ '$'
;
; device driver header
;
header dd -1 ; link to next device, -1 = end of list
dw 8000h ; device Attribute Word
dw strat ; device stratagy entry point
dw intr ; device interrupt entry point
db 'CTRL-BRK' ; character device name
rh_ptr dd ?
page
dispatch:
dw init
dw write
request struc
rlength db ?
unit db ?
command db ?
status dw ?
reserve db 8 dup (?)
media db ?
address dd ?
count dw ?
sector dw ?
request ends
page
msg_len dw ?
flag db 1 ; NOBRK turned ON or OFF (1 = ON, 0 = OFF)
kbseg dw SEG40 ; Keyboard Segment
int09: dw 0,0 ; Store KBD BIOS interrupt 09 hex vector here
strat proc far
mov word ptr cs:[rh_ptr],bx
mov word ptr cs:[rh_ptr+2],es
ret
strat endp
page
intr proc far
push ax ; save general registers
push bx
push cx
push dx
push ds
push es
push di
push si
push bp
push cs ; make local data addressable
pop ds
les di,[rh_ptr] ; let es:di = request header
mov bl,es:[di.command] ; get bx = command code
xor bh,bh
cmp bx,init_cmd ; check for init command
je intr1
cmp bx,read_cmd ; check for read command
jne test_write
mov ax,800bh
jmp intr2
test_write: cmp bx,write_cmd ; check for write command
jne cmd_error
mov bx,1
jmp intr1
cmd_error: mov ax,8003h ; set error bit and unknown command code
jmp intr2
intr1: shl bx,1 ; form index to dispatch table
call word ptr [bx+dispatch] ; and branch to driver routine
; should return ax=status
les di,[rh_ptr] ; restore es:di = addr of request header
intr2: or ax,0100h ; merge done bit into status, and
mov es:[di.status],ax ; store into request header
pop bp
pop si
pop di
pop es
pop ds
pop dx
pop cx
pop bx
pop ax
ret ; back to dos
page
write proc near
mov dx,es:[di]+14 ; offset of string
mov ds,es:[di]+16 ; segment of string
mov cx,es:[di]+18 ; number of bytes in string
mov cs:msg_len,cx ; store number of bytes on stack
cld
push ds
pop es
mov di,dx
mov al,'F' ; look in string for 'F'
repne scasb ; set cf = 0 if found, 1 if not
je brk_off ; jump if cf = 0
mov di,dx
mov al,'f' ; look in string for 'f'
mov cx,cs:msg_len ; restore number of bytes
repne scasb ; set cf = 0 if found, 1 if not
je brk_off ; jump if cf = 0
mov di,dx
mov al,'N' ; look in string for 'N'
mov cx,cs:msg_len ; restore number of bytes
repne scasb ; set cf = 0 if found, 1 if not
je brk_on ; jump if cf = 0
mov di,dx
mov al,'n' ; look in string for 'n'
mov cx,cs:msg_len ; restore number of bytes
repne scasb ; set cf = 0 if found, 1 if not
je brk_on ; jump if cf = 0
jmp done
brk_on: mov cs:flag,0
jmp done
brk_off: mov cs:flag,1
done: xor ax,ax
ret
write endp
chkkey: pushf ; Save all registers
push ax
push cx
push di
push si
push ds
push es
sti ; Allow other interrupts to occur
mov ax,cs
mov ds,ax ; Set DS to this segment
mov es,word ptr cs:kbseg ; Set ES to segment of keyboard buffer
mov si,kbflag ; 40:17H Where DOS keeps track of shift state
mov ah,es:[si] ; Get key input
; If OFF, then skip to exit, else see if we need to kill the Ctrl-C
; (AH contains the latest KBFLAG value)
test cs:flag,1 ; Ignore Ctrl-C or Ctrl-Break ?
jz exit ; Branch if OFF
test ah,ctrl ; Is Control Key pressed?
jz exit ; No, pass the key to BIOS routine
test ah,0bh ; Is ALT, LEFT or RIGHT SHIFT pressed ?
jnz exit ; No, pass the key to BIOS routine
in al,kbinctl ; Get the key code
cmp al,46 ; ^C?
je kill ; Yes, kill it
cmp al,70 ; ^BREAK?
jne exit ; No, exit to BIOS
;----- Kill ^C or ^BREAK
kill: in al,kbcmdp ; Read the KB command port
mov ah,al ; Copy it to AH
or al,80h ; Set RESET bit
out kbcmdp,al ; Write RESET to the command port
mov al,ah ; Clear the RESET bit
out kbcmdp,al ; and write to the command port
mov al,20h ; Send END OF INTERRUPT to the interrupt cont.
out 20h,al
pop es ; Restore all registers
pop ds
pop si
pop di
pop cx
pop ax
popf
iret ; Return to the interrupted routine
; Restore registers and exit to the DOS keyboard interrupt handler
exit: pop es ; Restore all registers
pop ds
pop si
pop di
pop cx
pop ax
popf
jmp dword ptr cs:int09 ; Exit to BIOS keyboard interrupt routine
init proc near
push es ; save address of request header
push di
mov ax,3509h ; Get Interrupt Vector function
int 21h ; Execute DOS function
mov word ptr int09,bx ; Store BIOS offset for INT 09
mov word ptr int09+2,es ; Store BIOS segment for INT 09
mov dx,offset chkkey ; New INT 09 vector
mov ax,2509h ; Set Interrupt Vector function
int 21h ; Execute DOS function
mov ah,9 ; print sign-on message
mov dx,offset message
int 21h
pop di ; restore request header addr
pop es
mov word ptr es:[di.address],offset init
mov word ptr es:[di.address+2],cs
xor ax,ax
ret
init endp
message db cr,lf
db 'CTRL-BRK - A device driver to intercept ctrl-brk and ctrl-c.'
db cr,lf
db '(C) 1987, 1988 John Pulliam, Walter Cox, and Benjamin Diss.'
db cr,lf,lf,eom
intr endp
page
driver endp
code ends
end