From owner-freebsd-hackers Wed Jan 3 09:40:22 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id JAA24077 for hackers-outgoing; Wed, 3 Jan 1996 09:40:22 -0800 (PST) Received: from who.cdrom.com (who.cdrom.com [192.216.222.3]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id JAA24068 for ; Wed, 3 Jan 1996 09:40:19 -0800 (PST) Received: from irz301.inf.tu-dresden.de (irz301.inf.tu-dresden.de [141.76.1.11]) by who.cdrom.com (8.6.12/8.6.11) with ESMTP id JAA07233 for ; Wed, 3 Jan 1996 09:39:47 -0800 Received: from sax.sax.de by irz301.inf.tu-dresden.de (8.6.12/8.6.12-s1) with ESMTP id SAA15109 for ; Wed, 3 Jan 1996 18:33:08 +0100 Received: by sax.sax.de (8.6.11/8.6.12-s1) with UUCP id SAA12835 for freebsd-hackers@freebsd.org; Wed, 3 Jan 1996 18:33:08 +0100 Received: (from j@localhost) by uriah.heep.sax.de (8.7.3/8.6.9) id RAA20736 for freebsd-hackers@freebsd.org; Wed, 3 Jan 1996 17:52:32 +0100 (MET) From: J Wunsch Message-Id: <199601031652.RAA20736@uriah.heep.sax.de> Subject: Re: POST checksum hacking To: freebsd-hackers@freebsd.org (FreeBSD hackers) Date: Wed, 3 Jan 1996 17:52:31 +0100 (MET) In-Reply-To: <199601030920.CAA24493@seagull.rtd.com> from "Don Yuniskis" at Jan 3, 96 02:20:33 am X-Phone: +49-351-2012 669 X-Mailer: ELM [version 2.4 PL23] MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: owner-hackers@freebsd.org Precedence: bulk As Don Yuniskis wrote: > > I'd like to cut a new set of EPROMs with an altered disk table > but the POST screams about bad checksums. Anyone have a clue as > to the algorithm employed and the location of the checksum image > (before I start disassembling code)? A ROM image consists of 0x55 0xaa - signature - number of 512-byte ``increments'' this ROM consists of *512-3 bytes ROM image The entire ROM image must byte-checksum to 0. This is usually done by placing a jump next after the byte, and reserving the byte after the jump instruction for checksumming. (I haven't verified this information.) -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)