EricBall's Tech Projects - advanced un-bankswitching idea

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One thing I find amazing about the 2600 homebrew scene is the strong interest in creating new bankswitching hardware, often with advanced capabilities. I think, very soon, the only remaining VCS limitations will be the capabilities of the TIA and that there are only 76 CPU cycles per line to update the TIA (hmm... shades of the GTIA/ANTIC).

 

Anyway, one idea which occurred to me is whether it would be possible for the cartridge to automatically bankswitch the 64K (32K usable) address space. Basically, the cartridge would snoop the address & data buses and pull the missing 3 address bits out of the data stream.

 

I've done some looking at the 6502 addressing modes and some intelligence & heuristics would be required. The cartridge would have to shadow the PC register so it can determine which data bytes are opcodes (for the correct addressing mode) and which are address MSBs. The tricky bit would be handling the extra fetch when indexed addressing goes over page boundaries and handling branches.

 

 

http://www.atariage.com/forums/index.php?a...;showentry=2346