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