Yes, that is essentially what I'm doing. The Arm does most of the heavy lifting for the actual game and the Z80 does input, sound, HUD, palette fading, hands+gun, main game loop, and of course it spends a lot of time just shuffling data to vram. RAM is limited so the KE04 internally renders to a 2 bitplane framebuffer (the bit-banding feature of KE04 greatly helps). When the Z80 needs the next frame it triggers an interrupt on the KE04 to wake it from sleep mode, it converts the framebuffer into GB vram ready tile + map attribute data and stores it on the dp-sram. Z80 can then DMA directly from dp-sram into vram. Some ranges in the dp-sram are for command buffers used for Z80<->KE04 communication.

The KE04 I am using has 128Kb ROM and 16Kb RAM, and lacks hardware division. This presents some interesting challenges in terms of memory and rom space usage, and juggling speed vs ram/rom usage. You could of course put something much beefier in there but I think that would take too much of the fun away from the project.

All in all it's great fun and I'm learning a lot as I go along. If I were to make another hardware revision I would use a CPLD instead of the MBC1 chip, and try to loose the dp-sram in favour of a normal sram.

Cheers, --Anders