I just had an idea for an even simpler devcart with no modifications to the actual cartridge. All it requires is some way to program the battery RAM of any cartridge, and a Game Genie.
The idea is to put your code into the battery RAM of a game, load the cartridge into your NES with a Game Genie attached, then enter a patch to jump to your code. You'd make the patch by running the game you're using in an emulator and finding where it first enables battery RAM (since most mapper chips power-up with it disabled), then making a Game Genie code that puts a JMP $XXXX just after that. If you were using an MMC1A game (The Legend of Zelda is the only one I know of), you could just patch the reset vector.
I'm about to make a Game Boy devcart (for APU experiments) and it seems there isn't anything like the MMC1A which has the battery RAM enabled at power-up, so I'm searching for alternate designs. I picked up a Game Genie to remove its cartridge connector from for the battery RAM programmer, but realized that maybe it would be more useful in its full function.
The idea is to put your code into the battery RAM of a game, load the cartridge into your NES with a Game Genie attached, then enter a patch to jump to your code. You'd make the patch by running the game you're using in an emulator and finding where it first enables battery RAM (since most mapper chips power-up with it disabled), then making a Game Genie code that puts a JMP $XXXX just after that. If you were using an MMC1A game (The Legend of Zelda is the only one I know of), you could just patch the reset vector.
I'm about to make a Game Boy devcart (for APU experiments) and it seems there isn't anything like the MMC1A which has the battery RAM enabled at power-up, so I'm searching for alternate designs. I picked up a Game Genie to remove its cartridge connector from for the battery RAM programmer, but realized that maybe it would be more useful in its full function.