It seems you indicate that you can get by, whatever the game (forget ED), if CD upgrade to SCD, or if SCD upgrade to ACD, etc. and thus avoid the need for creating your own custom system card based on what I read. But, you really like the idea even still ? My feeling/preference is for the upgrade route before going as far as the custom system card route, but yeah, you would know better as to what games are impossible to do without the latter. I'd just play it on an emulator if I was even interested in whatever future game you targeted using the idea.
Well, CD to SCD definitely. I did this for Dave's Cosmic Fantasy I project. SCD->ACD helps with having a place for the font to live outside the regular game (i.e. most games need a new font), and it can help with script compression issues (dictionary/string compression). But ACD still lacks in one thing; not extra space for replacement code. You can't always just overwrite the original game code. Sometimes it requires more space. One example is if the original print routine is complex and needs a lot of 'monitoring' and special case modification (you'd be surprised). Dead of the Brain required a LOT of this because of how the tiles and tilemap was setup. I basically ran out of space, which is why certain script stuff has to be manually don't with control codes on the script side and special attention to the format of the text. Which is why the project has stalled (needs special support utils to handle this pre-script insertion).
Here's how an easy to make hucard with the original 256k SCD bios rom with a full 512k (hell, even just 256k vs 192k) can help: on your boot code, you load a special modified system card bank $00 into ram and map this to MPR 7. Games
never change that, so once it's mapped - you're good to go. There is free space in the original rom's area, which is now ram, we can put our own custom call routines in there to the new ram. The original rom is there, making it compatible with original SCD games, *and* you have the ability to add upgrades by
simply reserving 8k for a new/alt sys card fix lib bank. It's so simple, it's genius.
I suggest 512k, because then homebrew could use it too. Why not get more purposes out of one card? And like I said, the card is super simple to make - no special hardware or mappers. You just need a hucard PCB that can accept two chips (one for lower 512k and one for upper 512k range).
Technically, I can do something similar with the SGX, because of the additional 24k of ram, but then I'm limiting all gamers to have an SGX. Arcade Cards are awesome, but they have a lot of tech in them and are more prone to failure (I've already have two of them die), and it doesn't address all issues. A PCB, like the one the french guy made (silk marked in white) would make the perfect SCD+extended ram card.
