> > your statement would also mean you have to "mark" every other rom-dump also as "NOT > > GOOD"...as long as you do not have a second dump from another board and another > > dumper! Even if the game is running in MAME or on real Hardware with the dump... > > as it could also be possible, that an normal eprom get's a bad bit on an area which > > is for example normally empty and not used... > > It's not as bad as that - if you work on the assumption that the programmer was sane > you can spend some time analysing a program to determine whether it's good. I'm very > confident that the MCU dumps for Bouncing Balls, Joshi Volleyball and Street Fight > are perfect. It helps that with Joshi Volleyball the MCU checksums program space on > boot, so many errors would be detected. > > I'm very confident that all but one bit of the MCU dump for Bad Dudes is good. That > one bit is in the implementation of a program checksum command that the game never > uses. It could be an original bug that prevented them from using the command in the > game, but given how obvious the bug is and that it's an EPROM part so the cost to fix > it would have been low (compared to redoing a mask ROM MCU), I think it's more likely > to be a single bit error in the dump. > > The Amiga 1200 keyboard MCU dump that we have passes a 16-bit program checksum, but > does contain a bad bit that means it only verifies one magic number rather than > several when deciding whether a reset was caused by NCOP. Since it passes its > checksum, I assume this is an original program bug that they didn't notice/fix > because it doesn't prevent it from working. > > Verifying a program like this is a lot of effort, so we're not going to be doing it > for every MCU (and I definitely don't have time to do personally for every MCU), but > it's definitely possible to do, and allows issues to be found in areas that aren't > used by the game.
for bad dudes (or was it dragon ninja) Data East intentionally corrupted / trashed some unused graphic tiles too, that's confirmed on several original boards, so that one-bit error could really be intentional.
but yeah, in that case extra verification isn't going to hurt.
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