TITLE	CRITERR.ASM
		SUBTTL	TRAP CRITICAL ERRORS FROM W/IN C

		IFDEF ??version			;TASM
		  %NOCONDS
		ELSE                            ;MASM
		  .SFCOND			;DONT SHOW FALSE CONDITIONALS
		ENDIF

; MODULE CRITERR.ASM
; JANUARY 1991
; PETER HYMAN (609) 799-2638
; 148 TENNYSON DRIVE
; PLAINSBORO, NJ  08536

; MODIFIED 2/16/91 SEE NOTES AT END OF SOURCE FOR DESCRIPTION OF CHANGES

;;;;; TWO FUNCTIONS ;;;;;

; FUNCTION NAME:  CRITERR( ONOFF )
; INPUTS 1 = TRAP CRITICAL ERRORS, 0 TURN OFF TRAP
; RETURNS 0 IF SUCCESSFUL, 1 IF ALREADY INSTALLED

; FUNCTION NAME:  CLRCRITERR( )
; CLEAR CRITICAL ERROR VARIABLES

; ON CRITICAL ERRORS, INT 24H HANDLER WILL RETURN AN IGNORE CODE TO DOS
; IF VERSION < 3, OR A FAIL CODE FOR DOS >= 3
; IF VERSION >= 3, DOS FUNCTION 59H IS CALLED ALSO, AND EXTENDED ERROR
; INFO IS ALSO PUT INTO STRUCTURE

;;;;; USES SIMPLIFIED SEGMENT DIRECTIVES.  ASSEMBLE WITH I8086S, M, C OR L
;;;;; DEFINED

;;;;; ASSEMBLE AS MASM/TASM /mx /dI8086[S|M|C|L] criterr;
;;;;; TURBO ASSEMBLER YIELDS SMALLER CODE WITH /Q OPTION

	IFDEF I8086S
		.MODEL	SMALL
		p equ 4			; p is offset into stack for args
		SCODE EQU 1
	ENDIF
	IFDEF I8086M
		.MODEL	MEDIUM
		p equ 6
		LCODE equ 1
	ENDIF
	IFDEF I8086C
		.MODEL	COMPACT
		p equ 4
		SCODE EQU 1
		LDATA EQU 1
	ENDIF
	IFDEF I8086L
		.MODEL	LARGE
		p equ 6
		LCODE EQU 1
		LDATA EQU 1
	ENDIF
	IFNDEF I8086S
	IFNDEF I8086M
	IFNDEF I8086C
	IFNDEF I8086L
		%OUT  NO MEMORY MODEL SPECIFIED
		END
	ENDIF
	ENDIF
	ENDIF
	ENDIF

;;;;; FORMAT FOR CRITICAL ERROR  HEADER BLOCK ;;;;;
;;;;; CERTAIN CHAR VARIABLES EXPANDED TO INT FOR PROPER ALLIGNMENT ;;;;;
CERR		STRUC  	; critical error structure
ceflag          db   ?  ; flag to indicate critical error 1 = yes
cerrno	  	db   ?	; critical error number  ; 2/16/91 changed to byte
cerrtype  	dw   ?	; critical error type/action/drive, AX
drive		db   ?  ; drive letter as a char
read_wr		db   ?  ; read or write error 1 = write
disk_area	db   ?  ; area of error, 0 = dos area, 1 = fat, 2 = dir, 3 = data
resp_mask	db   ?  ; allowable responses (moot)
exterr		db   ?  ; extended error number  DOS >= 3 2/16/91 changed to byte
eclass		db   ?  ; error class
action		db   ?  ; action recommendations
locus		db   ?  ; locus
nextdev   	dd   ?  ; next device pointer
attr      	dw   ?  ; device attribute
nxtfunc   	dw   ? 	; pointer to next strategy function
intfunc   	dw   ?  ; pointer to interrupt function
devname	  	db   8 dup(?)	; device name
dummy	  	db   ?  ; terminating null
CERR	ENDS

; SEE DOS TECHNICAL REFERENCE FOR EXPLANATION OF CODES


;;;;; BEGIN DATA SEGMENT ;;;;;  USING SIMPLIFIED SEGMENT DIRECTIVES

	.DATA			; begin data segment
	extrn __osmajor:byte	; operating system version
_criterrtrap 	db 0 		; critical error flag 1=trapped, 0 = off
;;;;; 	GLOBAL  ;;;;;
	public _cerr      	; GLOBALS
_cerr	CERR <>	 	        ; CRITICAL ERROR STRUCTURE BLOCK

	.DATA?			; uninitialized data
_oldint24vec  	label  dword
_oldint24off 	dw ? 		; static vector to int 24 before trap
_oldint24seg 	dw ? 		;


; PROCEDURE CRITERR( ONOFF )
; SETS ALTERNATE CRITICAL ERROR HANDLER
; USAGE:	criterr( 1 ) to set, criterr( 0 ) to turn off

	.CODE			; begin code segment

savds	dw	0		; save proper data segment

	public _criterr
ifdef SCODE
_criterr	proc
else
_criterr	proc	far
endif
	push bp
	mov bp, sp
	push si
	push di
	mov ax, p[bp]		; see if a 0 or 1 was passed
	test ax, ax		; non zero?
	jne settrap             ; 1, so set trap
removetrap:
	cmp _criterrtrap, 1	; see if installed
	jne done        	; not installed, so return
	push ds
	lds dx, _oldint24vec	; restore original int 24 vector
 	mov ax, 2524h
 	int 21h      		; dos set vector function
 	pop ds
	mov _criterrtrap, 0	; reset flag
	xor ax, ax		; set return code
	jmp done
settrap:
	cmp _criterrtrap, 1	; see if installed
	je  done        	; yes, so return (AX = 1)
	mov cs:savds, ds 	; move current data segment to savds
 	push	es
 	mov	ax,03524h	; save old vector to int 24
 	int	021h
	mov _oldint24off,bx
	mov _oldint24seg,es
	pop	es
	push	ds
	mov	dx, offset cs:int_service	; load address of new routine
	mov	ax,cs
	mov	ds,ax
	mov	ax,02524h     	; set it
 	int	021h
	pop	ds
	mov _criterrtrap, 1	; set flag
	xor ax, ax	 	;set return code

done:
	push ax                         ; save AX
	ifdef LCODE
	call far ptr _clrcriterr 	; reset values
	else
	call _clrcriterr
	endif
	pop ax
	pop di
	pop si
	pop bp
	ret			; return to caller, return code in AX


;;;;; NEW CRITICAL ERROR HANDLER ;;;;;
;;;;; SEE DOS TECHNICAL REFERENCE ;;;;;

int_service: 			;int 24 trap goes here
	push	bp
	mov	bp,sp           ; set to critical stack frame
	push	bx              ; all used registers except AX must be
	push	cx              ; saved !!!!!
	push	dx
	push	si
	push	di
	push	ds
	push	es
	pushf
	mov	ds,cs:savds 	; reset ds to program's ds
	mov 	bx, di          ; save DI
	mov     di, offset _cerr  ; set di to point to structure cerr
	mov     ceflag[di], 1   ; set ceflag 2/16/91
	mov	cerrno[di], bl	; move to cerrno -- move byte only 2/16/91
	mov	cerrtype[di],ax	; save error type/drive number
	test	ax, 8000h	; char or block device
	mov	bx, ax
	jnz	response	; char device, so skip
	add	bl, 'A'		; add letter A
	mov	drive[di], bl	; move drive over
	and	bh, 00000110b	; leave only bits 1 and 2
	shr	bh,1		; shift it over 1
	mov	disk_area[di], bh ; save area of error
	mov	bh, ah
response:                       ; determine response possibilities
	and	bh, 1           ; 2/16/91 this block moved from prev para.
	mov	read_wr[di], bh ; move read write flag
	mov	bh, ah
	and	bh, 00111000b	; leave only bits 3-5
	shr	bh,1
	shr	bh,1
	shr	bh,1		; shift it over
	mov	resp_mask[di],bh ; save response mask
move_dev_header:		; move device header block
	push	ds              ; set up data registers
	pop	es
	mov	bx,[bp]		; load bp to get segment for device header
	mov	ds,bx           ; si contains offset of device header
	mov	di,offset _cerr.nextdev	; copy device header block
	cld
	mov	cx,9
	rep 	movsw	    	; move 18 bytes of device header block
	push	es
	pop	ds              ; restore data registers

	; now check for DOS version
	xor	ax,ax		; return code ignore for dos < 3
	cmp	__osmajor,3	; dos >= 3?
	jl	doneint		; no
	; prepare to get extended error
        mov 	bx, 0
	mov	ah, 59h		; get dos extended error
	int	21h		; call dos
	mov	di, offset _cerr; set di to point to cerr structure
	mov	exterr[di], al	; error code  -- move byte only 2/16/91
	mov	eclass[di], bh  ; error class
	mov	action[di], bl  ; action
	mov     locus[di],  ch  ; locus
	mov     al, 3		; return fail code
doneint:
	popf
	pop	es
	pop	ds
	pop	di
	pop	si
	pop	dx
	pop	cx
	pop	bx
	pop	bp		; restore stack frame
	iret			; return from interrupt
_criterr	endp

;;;;;	FUNCTION TO CLEAR CRITICAL ERROR STATUS ;;;;;

;;;;; USAGE:  clrcriterr()

	public _clrcriterr
ifdef SCODE
_clrcriterr	proc		; function to clear critical error number
else
_clrcriterr	proc   far	; function to clear critical error number
endif

	push bp
	mov bp,sp
	push di
	push ds
	pop es
	xor ax,ax		; zero entire structure
	mov di, offset _cerr
	mov cx, size _cerr	; get size of entire block
	rep stosb
	pop di
	pop bp
	ret
_clrcriterr	endp

end

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; PROGRAM MODIFICATIONS
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; MODIFIED 2/16/91 TO INCLUDE THE FOLLOWING
; STRUCTURE MEMBER ceflag ADDED
;  THIS WAS REQUIRED TO DETECT CRITICAL ERRORS, SINCE cerrno COULD HAVE
;  A VALUE OF 0 WHICH WOULD INDICATE A WRITE PROTECT ERROR.  ceflag WILL
;  BE SET IT THERE WAS A CRITICAL ERROR
; CALLS TO EXTERNAL FUNCTION _dos_exterr REMOVED
; STUCTURE MEMBERS cerrno AND exterr CHANGED TO BYTE SIZE
; STRUCTURE MEMBER pad REMOVED BECAUSE ABOVE MADE IT UNNECESSARY
; THE CODE WHICH SET THE read_wr STRUCTURE MEMBER WAS MOVED TO JUST
;  BELOW THE response: LABEL SINCE IT WAS NOT CORRECTLY LOCATED PREVIOUSLY
;  AND WOULD NEVER BE SET FOR NON-DISK ERRORS
; TESTS TO SEE IF HANDLER WAS ALREADY INSTALLED WERE CHANGED.  IT WAS
;  POSSIBLE TO INSTALL THE HANDLER MULTIPLE TIMES THEREBY REMOVING THE
;  ABILITY TO UNINSTALL IT. CODE AFTER removetrap: AND settrap: WAS MODIFIED
;  TO COMPARE FLAG.
; cerr STRUCTURE WILL BE RESET WHENEVER THE CRITERR FUNCTION IS CALLED.  IF
; IS INSTALLED, REMOVED.