MESS emulator

[Fraser]

Why does the MESS BBC emulator say the checksum is wrong with the Watford DFS 1.44 rom from this site?

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[bbcfan]

Because it is. Although whether the ROM will behave any differently than the verified version, I don't know.<br>
<br>
The only differences of the two files detailed below.<br>
<br>
Offset STH MESS<br>
&7CB 01 02<br>
&7CD E0 C0<br>
&7CE 01 03<br>
&7CF 04 08<br>
&7D0 E0 C0<br>
&7D1 01 03<br>
&7D2 01 19<br>
&7D3 E0 C4<br>
&7D4 02 0C<br>
&7D5 08 0A<br>
&7D6 EF C8<!--EZCODE EMOTICON START :rolleyes --><img src=http://www.ezboard.com/images/emoticons/eyes.gif ALT=":rolleyes"><!--EZCODE EMOTICON END-->

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[Fraser]

Where did you get the other file? The other required files I got from some of the other emulators. It looks like the STH file is modified. It should be named to indicate this if this is the case.

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[billcarr]

(Change of USER id)<br>
<br>
I compared the STH file with the one with BeebEM 1.60, wdfs.rom<br>
<br>
It can be hard to tell if a file is "correct", it may be that the MESS crc is calculated from the rom image that is the easiest to get hold of. I only have Watford DFS 1.43 in my BBC - and not an original rom at that, so I cannot check the authenticity.<br>
<br>
(This is why I like to get games, and try to transfer them to an emulatable format without needlessly modifying text within the files, or filenames, etc. to make sure they are as "correct" as possible)

<p></p><i>Edited by: <A HREF=http://p198.ezboard.com/bthestairwaytoh ... illcarr</A> at: 22/11/04 9:48 pm<br></i>

[Fraser]

The CRC is part of the Acorn ROM format. The Electron AUG has something on it at P176. The CRC is probably calculated the same as with tape blocks. I could write a program to check checksums but MESS appears to do it anyway.<br>
<br>
I have a ROM with E2P on it. Any idea what it is? It could be the PMS E2P Electron 2nd processor cartridge rom.

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[billcarr]

Not sure what you mean. The CRC is just a checksum so that MESS knows that the correct file is being loaded, and not just some other file called dfs144.rom<br>
Of course some ROMs & files would have checksums to check for any modification.<br>
<br>
Going off on a slight tangent, I remember that Elite has a catalogue checksum to test whether the disc is original, since the chances of having exactly the same number when all filenames/details are added together from another disc are slim. Can't think of any more atm.

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[Fraser]

The MESS checksums might only be an accumulated sum of all bytes. I don't know yet if the Acorn CRC in tape blocks is any particular type.

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[Fraser]

My unknown ROM is E2PCODE ROM, (C) 1986 John Wike. Is there a program for writing ROMs to disk or tape?

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