Friday 26 June 2009

Bubble Bobble Bootleg Bonanza

Let me introduce my first little project. It's a bit all over the shop but I'll try to cram it all in.

Back in the 80's a company called Taito released one of , if not THE most popular arcade platformer of all time. Bubble Bobble. Because of its popularity it became an obvious target for one of the more shady aspects of arcade gaming .. bootlegging.

From a bootleggers point of view, getting a game working 100% identical to the original is the ideal but no where near as important as getting it to work closely enough to sell. The amount of time where its possible to make a decent profit from selling a bootlegged copy is relatively small so shortcuts are taken.

Knowing this, the Taito engineers included on the board a special custom MCU. Labeled with their own custom markings the JPH1011P or "PS4" shared an on board RAM chip with one of the Z80 processors on the board , modifying various aspects throughout the game. It was of course protected so that once programmed it's internal programming could not be read back out.




Cute.

The bootleggers bypassed the need for the PS4 in a couple of ways.

One set "blackboxed" the PS4. By this i mean they ran the original board and monitored what parts of the shared ram it was reading and writing to. They then created their own version of the PS4 in a programmable part available at the time, a Motorola 68705.

Another set of bootleggers modified the Z80 program entirely to disable all checks for the PS4 and recreate the functions of it within the Z80 code itself. This type of bootleg board (to me at least) seems to be the more common. One other aspect of this type of board (which is what this whole idea leans on) is that it is layed out in most cases EXACTLY the same as the original Taito PCB.

Unfortunately what both sets failed to do is mimic the PS4's behaviour exactly, hardly surprising with some of the functions only being triggered by obscure events or only after extended periods of playing time . Because of this, certain aspects of the game such as the randomness of the EXTEND bonuses, enemy movements or the clock bonus item do not work as expected.

The MAME arcade emulator for a long time had incomplete emulation of the game for the above reasons until recently they were able to decapsulate and extract the program contents of the PS4. This resulted in perfect emulation as well as giving the public a peek at the original code.

So finally ... my idea.

I'm thinking that it should be possible to recreate a compatible version of the PS4 using a modern micro controller such as a PIC or AVR. It could be used as a fully functional replacement to revive an original PCB that has a faulty PS4 but as an eventual goal i would like to be able to upgrade compatible bootleg pcbs to function exactly like an original.

Pointless ... maybe
Useful ... only to a select few
Tons of tinkering, finger burning, code hacking fun .. hell yeah :)

1 comment:

  1. Hey Paul, what happened with this project? did anything about it? It would be great!!

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