Recover damaged CPU Diagnostic ROM

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Recover damaged CPU Diagnostic ROM

Post by MADrigal » Tue May 16, 2023 10:59 am

Hi all
Some may remember my post from 30 Jan 2023 on the CreatiVEmu website, in relation to my defective dump of the insanely rare "CPU Diagnostic Test". The story is quoted below:
Around 2008 I purchased an insanely rare cartridge containing a diagnostic program to test the CreatiVision 6502 CPU. This cartridge was definitely a VTech original: not a commercial product but "for internal use". It was found (one copy only) in the warehouse of the (now closed) official CreatiVision repair centre in Italy, owned by Zanussi Elettronica.
I believe VTech provided each repair centre with one copy of such cartridge. This would mean that just a handful of cartridges are in existence. The one in my possession is the only one I have ever seen or heard about.
The cartridge worked well when I first tested it, but then when the EPROM was unsoldered (so that it could be dumpet), it got slightly damaged. The dump is there, but it is partial. I then sent the EPROM to a MAME team member who was in charge to repair it - but he lost it.
Since 2010, no one knows where my one-of-a-kind EPROM is.

I have decided to release all my partial dumps of the EPROM, together with information and a Hex editor tool I created many years ago specifically to work on this ROM. I hope that one day, someone will be able to fix this rare file.
This ended up in long time CreatiVision enthusiast Andrew Davie starting a topic on the AtariAge forum - calling for arms and help from programmers and coders to solve this "puzzle". Some people came with interesting ideas ... challenge/

Today I received the below email from a gentleman called Chris:
Iv been looking at the EPROM CPU dump
Iv come up with an idea to maybe get it working once again. However it is quite a long shot.
And would probably require help from the community.
My thought was that if only bit 1 and 6 are damaged than we could try a custom brute force attack/fix
That would simple change each bit 1 and 6, one at a time and wright the new changes to a file.
Then some small changes to the source code of a emulator to attempt to load the rom/new file. if it works
don’t actually run the rom just return true to the main program. And process accordingly.

I know this would take a long time to run/complete that’s where
If we spread the work load with the community than just maybe it will work?

Let me know what you think.
Honestly I am not in the position to provide any help on this, but I thought that someone out there may be interested in taking the challenge?

I am happy to provide you with Chris' contact details if you wish to speak to him directly
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Joined: Thu May 18, 2023 9:51 am

Re: Recover damaged CPU Diagnostic ROM

Post by chrisnewm » Thu Jun 08, 2023 12:06 am

Hi everyone. I've been working on the CPU cart recently and whipped up a little tool to help me with it. what it does is take a byte entered and swaps bits 1 and 6 respectively. To show all combination that byte could have been as well as print out the 6502 opcode next to it.

Thought if anyone else is working on this task this might help them out. do let me know of any bugs thanks.

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