Scraping the Barrel pt2

The previous post has undergone many updates and revisions now, so I feel it’s time to make a fresh one.

Since that post, Olivier has mostly fixed up the System 24 regressions, although Gain Ground is stuck in a freeplay mode / no dipswitch reading mode due to some weird code (see driver notes) but the majority of the other tasks remain on the table.

Most of the things mentioned in this post will be a bit harder than the ones previously mentioned, but still might be of interest. Again, this list will be revised multiple times.

MPU4 Video System – Protection + More

The ‘Skill Wins Prizes’ video games, based off the MPU4 fruit machine driver still needs work. While all games have issues with the video refresh being far too slow (taking several seconds for the cursor to change position in The Crystal Maze, for example) there is a more serious issue with the protection devices, especially noticeable on the Quiz games.

The hardware uses a PAL of some kind to scramble the quiz data, this works as a challenge + response system, but it isn’t a simple 1:1 mapping, the same challenge can result in a different response depending on previous writes, and the internal state of the device. The end result of this is that the questions (for games where questions are actually dumped, many sets are incomplete) appear as garbage. They use some kind of dictionary system to compress the questions too (done in software) which makes it less clear. The current protection handling code in all the MPU4 games is just a hack which allows the startup tests to pass. Some of the fruit machines don’t do any further checks beyond tho, so in those cases it’s sufficient, but in the case of the quiz games it certainly isn’t. See ‘TurnOver’ for example.

Black Touch ’96 – Video and Sound

The PIC was decapped, nobody has hooked it up yet. This drives the OKI sound chips.
The video system appears to be something close to Seta / Suna systems, with sprites (and backgrounds) being made of tile ‘strips’. The hookup isn’t quite right at the moment. This might be pretty easy actually.






News Source: Here