Path: utzoo!attcan!uunet!lll-winken!ames!ncar!hao.ucar.edu!hull
From: hull@hao.ucar.edu (Howard Hull)
Newsgroups: comp.sys.amiga
Subject: Insider RTClock fix detail
Keywords: branch offset
Message-ID: <1334@ncar.ucar.edu>
Date: 27 Jan 89 20:46:01 GMT
Sender: news@ncar.ucar.edu
Reply-To: hull@hao.ucar.edu (Howard Hull)
Organization: High Altitude Observatory/NCAR, Boulder CO
Lines: 66

I have the following (via USnail) from Jack Aker, who does not have Usenet
posting access.  I haven't had a chance yet to check it against my Insider
RTClock modules, since I am doing this on my A2000 at work, and the Insiders
are installed in my A1000s at home.
-soh-

							January 20, 1989

The RTClock program provided with the Insider memory board from
Michigan Software has a "year after leap year" bug.  The program
reads and displays the correct date, but the DOS value set is one
day earlier than the displayed date.

The two code segments below show the bug and the correction for
it.

?U DoIO+8b0
00c7eb28: 202e ffe4		move.l	-1c(a6),d0
00c7eb2c: 7204			moveq	#4,d1
00c7eb2e: 4eb9 00c7 f458	jsr	c7f458
00c7eb34: 5581			subq.l	#2,d1
00c7eb36: 6612			bne.s	*+12 ;c7eb4a ;wrong place
00c7eb38: 0cae 0000 0002 ffe8	cmpi.l	#2,-18(a6)
00c7eb40: 6f08			ble.s	*+8 ;c7eb4a
00c7eb42: 06ae 0001 5180 fffc	addi.l	#15180,-4(a6)
00c7eb4a: 206e 0008		movea.l	8(a6),a0
00c7eb4e: 20ae fffc		move.l	-4(a6),(a0)

This is what the above code segment should be:
?U DoIO+8b0
00c7eb28: 202e ffe4		move.l	-1c(a6),d0
00c7eb2c: 7204			move.q	#4,d1
00c7eb2e: 4eb9 00c7 f458	jsr	c7f458
00c7eb34: 5581			subq.l	#2,d1
00c7eb36: 6608			bne.s	*+8 ;c7eb40 ;correct
00c7eb38: 0cae 0000 0002 ffe8	cmpi.l	#2,-18(a6)
00c7eb40: 6f08			ble.s	*+8 ;c7eb4a
00c7eb42: 06ae 0001 5180 fffc	addi.l	#15180,-4(a6)
00c7eb4a: 206e 0008		movea.l	8(a6),a0
00c7eb4e: 20ae fffc		move.l	-4(a6),(a0)

Use a binary file zap tool to change the '6612' to '6608', which
will correct the wrong branch destination.

The byte to change from 12 hex to 08 hex is at the following
places in the different versions as shown:

RTClock	size	date		offset in file
V ??	8864	12-Feb-87	90F
V2.0	8904	16-Sep-87	9CB

There may be other versions of RTClock.  If your copy doesn't
match either of the versions above.  Search for the hex string:
 5581 6612 0cae 0000 0002 ffe8 6f08 06ae 0001 5180
	||
	08  goes here

There should be only one place in the file with this string.

						Jack Aker
						6944 Burnside Dr.
						San Jose CA 96120

-eom-
Posted by					Howard Hull
						hull@hao.ucar.edu