Nintendo’s technical docs say that GamePaks can provide extra RAM in the $06000000-$06FFFFFF memory region.

So … I’m wondering, did any shipped games actually use that memory region? Perhaps for battery-backed saves?

Yes. On those cartridges, as well as the FlashBoy Plus, there are 8 kilobytes of SRAM, accessed as halfwords so every other byte is valid.

OK, thanks! I guess that I’ll find another way to increase the amount of the VB’s RAM (in the mednafen emulator, for debugging during development).

It’s possible to put 16-bit-wide RAM there (or in the Expansion Area at 0×04000000-0x04FFFFFF) and run code from it.

This would only be for development/debugging usage, and not for actual cartridges.

It’s questionable whether it’s even needed on the VB, since you can just make the cartridge image bigger … but it never hurts to have more ram for debug traces.

Putting it in the $04000000-$04FFFFFF region seems like it should be pretty safe.