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PAGE ,132
; Install an Interrupt 24 (DOS critical error exception) handler
;
; Public domain by Bob Stout
;
; Requires MASM 5.1 or later or equivalent
;
; Assemble with: MASM /Mx /z ...
; TASM /jMASM /mx /z ...
% .MODEL memodel,C ;Add model support via command
;line macros, e.g.
;MASM /Dmemodel=LARGE
.DATA?
PUBLIC cedevdvr, cetype, ceerror, cereturn
_origvec dd ?
_newvec dd ?
cedevdvr dd ?
cetype dw ?
ceerror dw ?
cereturn db ?
.CODE
;
; This is our actual ISR
;
myint24:
push ds ;save registers which may be
push es ;required in case "Retry" is
push bx ;selected
push cx
push dx
push si
push di
push bp
mov word PTR cedevdvr,si ;save device driver header address
mov word PTR cedevdvr+2,bp
mov cetype,ax ;save error type information
mov ceerror,di ;save error code information
call far PTR _newvec ;call our handler
mov al,cereturn ;set up return code (abort, retry...)
pop bp ;restore necessary registers
pop di
pop si
pop dx
pop cx
pop bx
pop es
pop ds
iret
;
; Call this to install our ISR
;
; void (_far *)() ins24(unsigned short segm, unsigned short offs);
; void (_far *)() ins24((void _far *handler)());
;
; Paramters (option 1) - 1 : Segment of handler
; 2 : Offset of handler
;
; Paramters (option 2) - 1 : Address of handler
;
; Returns pointer to old handler
;
ins24 PROC USES AX BX DS ES, segm:WORD, offs:WORD
mov ax,3524h ;get old vector...
int 21h
mov word PTR _origvec,bx
mov word PTR _origvec+2,es ;...and save it
mov ax,offs ;load handler offset...
mov word PTR _newvec,ax
mov ax,segm ; & segment into _newvec
mov word PTR _newvec+2,ax
push cs ;get myint24 segment in DS
pop ds
mov dx, OFFSET myint24 ;install myint24 in int 24h
mov ax,2524h ; into Interrupt 24h
int 21h
mov ax,word PTR _origvec
mov dx,word PTR _origvec+2
ins24 ENDP
;
; Call this to uninstall our ISR
;
; void redo24(void);
;
redo24 PROC USES AX BX DS
mov dx, word PTR _origvec ;restore original vector
mov ds, word PTR _origvec+2
mov ax,2524h
int 21h
ret
redo24 ENDP
end
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