LX9R3-BASED USB MEGADRIVE DEVKIT

You'll need an lx9/r3 board:

https://github.com/makestuff/lx9/tree/r3

...and a umdkv2-lx9/r1 board:

https://github.com/makestuff/umdkv2-lx9/tree/r1

You can then follow the instructions in the Wiki:

https://github.com/makestuff/umdkv2/wiki