; By Steve Holzner (from June 11, 1985 issue of PC Magazine)



interrupts	segment at 0h	; This is where the disk interrupt

	org	13h*4		; holds the address of its service routine

disk_int	label	dword

interrupts	ends



screen	segment at 0B000h	; A dummy segment to use as the Extra

screen	ends			; Segment so we can write to the display



code_seg	segment

	assume	cs:code_seg

	org	0100h		; ORG = 100h to make this a .COM file

first:	jmp	load_watch	; First time through jump to initialize routine



	msg_part_1	db	'Disk error: '	; Here are the error messages

	msg_part_2	db	'No response Failed Seek NEC Error   '

			db	'Bad CRC SeenDMA Overrun Impos Sector'

			db	'No Addr MarkW. ProtectedErr Unknown '

	first_position	dw	?		; Position of 1st char on screen

	flags		dw	?

	screen_seg_offset dw	0		; 0 for mono, 8000h for graphics

	old_disk_int	dd	?		; Location of old disk interrupt

	ret_addr	label dword		; Used in fooling around with

	ret_addr_word	dw 2 dup(?)		;   the stack



disk_watch	proc	far	; The disk interrupt will now come here

	assume	cs:code_seg

	pushf			; First, call old disk interrupt

	call	old_disk_int

	pushf			; Save the flags in memory location "FLAGS"

	pop	flags		; (cunning name)

	jc	error		; If there was an error, carry flag will have

	jmp	fin		;  been set by Disk Interrupt

error:	push	ax		; AH has the status of the error

	push	cx		; Push all used registers for politeness

	push	dx

	push	di

	push	si

	push	es

	lea	si,msg_part_1	; Always print "Disk Error: " part.

	assume	es:screen	; Use screen as extra segment

	mov	dx,screen

	mov	es,dx

	mov	di,screen_seg_offset	; DI will be pointer to screen position

	add	di,first_position	; Add to point to desired area on screen

	call	write_to_screen		; This writes 12 chars from [SI] to [DI]

	mov	dx,80h			; Initialize for later comparisons

	mov	cx,7			; Loop seven times

e_loop:	cmp	ah,dh			; Are error code and DH the same?

	je	e_found			; If yes, Error has been found

	add	si,12			; Point to next error message

	shr	dh,1			; Divide DH by 2

	loop	e_loop			; Keep going until matched  DH = 0

	cmp	ah,3			; Error code no even number; 3 perhaps?

	je	e_found			; If yes, have found the error

	add	si,12			; Err unknown; unknown error returned

e_found:call	write_to_screen		; Write the error message to the screen

	pop	es		; Restore the registers

	pop	si

	pop	di

	pop	dx

	pop	cx

	pop	ax

fin:	pop	ret_addr_word		; Fooling with the stack. We want to

	pop	ret_addr_word[2]	; preserve the flags but the old flags

	add	sp,2			; are still on the stack. First remove

	push	flags			; return address, then flags. Fill flags

	popf				; from "FLAGS", return to correct addr.

	jmp	ret_addr

disk_watch	endp



write_to_screen	proc	near	; Puts 12 characters on screen

	mov	cx,12		; Loop 12 times

w_loop:	movs	es:byte ptr[di],cs:[si] ; Move to the screen

	mov	al,7		; Move screen attribute into screen buffer

	mov	es:[di],al

	inc	di		; Point to next byte in screen buffer

	loop	w_loop		; Keep going until done

	ret

write_to_screen	endp



load_watch	proc	near	; This procedure initializes everything

	assume	ds:interrupts	; The data segment will be the interrupt area

	mov	ax,interrupts

	mov	ds,ax



	mov	ax,disk_int	; Get the old interrupt service routine

	mov	old_disk_int,ax	; address and put it into our location

	mov	ax,disk_int[2]	; OLD_DISK_INT so we can call it.

	mov	old_disk_int[2],ax



	mov	disk_int,offset disk_watch  ; Now load the address of DskWatch

	mov	disk_int[2],cs		; routine into the disk interrupt



	mov	ah,15		; Ask for service 15 of INT 10h

	int	10h		; This tells us how display is set up

	sub	ah,25		; Move to twenty five places before edge

	shl	ah,1		; Mult. by two (char & attribute bytes)

	mov	byte ptr first_position,ah	; Set screen cursor

	test	al,4		; Is it a monochrome display?

	jnz	exit		; Yes - jump out

	mov	screen_seg_offset,8000h	; No, set up for graphics display

exit:	mov	dx,offset load_watch	; Set up everything but this program to

	int	27h			; stay and attach itself to DOS

load_watch	endp

	code_seg	ends

	end	first	; END "FIRST" so 8088 will go to FIRST first.