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70 lines
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TITLE BRK2 -- Break Handling Utilities Module
TRUE EQU 01H ;boolean true
FALSE EQU 00H ;boolean false
BREAKINT EQU 23H ;dos control-break intrpt
GETVECTOR EQU 35H ;dos get vector function
SETVECTOR EQU 25H ;dos set vector function
DOS_FUNCTION EQU 21H ;dos function call
BREAK SEGMENT PUBLIC 'CODE'
BREAKFLAG DB 0H ;break key hit flag
SAVEBRK DD 0H ;saved break vec. contents
ASSUME CS:BREAK
ASSUME DS:NOTHING
;CHECK_BREAK checks if ctrl-break has been pressed. It returns
;true if ctrl-break has been pressed and false if it hasn't.
PUBLIC CHECK_BREAK
CHECK_BREAK PROC FAR
XOR AX, AX ;clear ax
MOV AL, BREAKFLAG ;return value = breakflag
MOV BREAKFLAG, FALSE ;reset breakflag
RET
CHECK_BREAK ENDP
;INSTALL_BREAK_HANDLER sets up a ctrl-break interrupt handler. It
;also saves the address of the former break handler so that it can
;be restored later.
PUBLIC INST_BRK_HANDLR
INST_BRK_HANDLR PROC FAR
PUSH DS
MOV AL, BREAKINT ;AL = break interrupt
MOV AH, GETVECTOR ;AH = dos function code
INT DOS_FUNCTION ;call dos
MOV WORD PTR SAVEBRK, BX ;save offset in int vector
MOV WORD PTR SAVEBRK+2, ES ;save base in int vector
MOV AL, BREAKINT ;AL = break interrupt
MOV AH, SETVECTOR ;AH = dos function code
MOV DX, OFFSET BRK_HANDLER ;DX = offset of brk handler
MOV BX, CS ;BX = this segment
MOV DS, BX ;DS = this segment
INT DOS_FUNCTION ;call dos
POP DS
RET
INST_BRK_HANDLR ENDP
;BRK_HANDLER is invoked by the bios when ctrl_break is pressed
BRK_HANDLER PROC FAR
MOV BREAKFLAG, TRUE ;breakflag = yes, break hit
IRET
BRK_HANDLER ENDP
;REMOVE_BREAK_HANDLER restores the previous ctrl-break handler
REM_BRK_HANDLR PROC FAR
PUSH DS
MOV AL, BREAKINT ;AL = break interrupt
MOV AH, SETVECTOR ;AH = dos function code
MOV DX, WORD PTR SAVEBRK ;DX = saved 1st word
MOV BX, WORD PTR SAVEBRK+2 ;BX = saved 2nd word
MOV DS, BX ;DS = saved 2nd word
INT DOS_FUNCTION ;call dos
POP DS
RET
REM_BRK_HANDLR ENDP
BREAK ENDS
END