I built my own Sega Genesis (Mega Drive) hardware dev kit from scratch
I feel like this would be an inferior development experience in 2022 compared to this approach: <a href="https://hackaday.io/project/1507-usb-megadrive-devkit" rel="nofollow">https://hackaday.io/project/1507-usb-megadrive-devkit</a><p>Which is an fpga in the cartridge that also serves as a gdb stub over serial.
You can debug with gdb directly on the hardware.