there are still some issues left to solve on my #Game Boy Cartridge plus Programmer project, that I want to solve this weekend [proud moment]. After that I will pin down the hardware. maybe an atmega32 would be an option as well for the "SRAM" part, but a faster atsamd21 seems more reasonable.

https://www.insidegadgets.com/2011/04/23/emulating-the-nintendo-logo-on-the-gameboy/

this tells me I should be safe with an ESP12 as an MBC1 controller. I need 8 pins for the cartridge and 3 for SPI to control the AVR. I don't need the data pins to be connected, I can use the AVR for that.

The next thing would be the SRAM. This will be handled by an ATSAMD21 / adafruit feather M0 (logger) board. It has 20 pins available, so I won't be able to fake an 8k SRAM. That would take 13 pins for address, 8 data and 3 control pins. Since I also need to connect SPI, I have 17 pins left. I need 11 pins for data and control, that makes 64 bytes fake SRAM.

Maybe I can use the ESP to make the AVR read the data pins and switch banks via SPI later.