Custom firmware for the Game and Watch: Super Mario Bros. console.

What is this?

This repo contains custom code as well as a patching utility to add additional functionality to the stock Game and Watch firmware.

Features

• Works correctly with retro-go in internal flash bank 2.
• Press button combination (LEFT + A + GAME) to launch retro-go from internal flash bank 2.

Usage

Place your internal_flash_backup.bin and flash_backup.bin in the root of this repo. To extract these from your console, see the game and watch backup repo

Install python dependencies via:

pip install -r requirements.txt

To just build and flash, run:

make flash

Advanced usage

Other potentially useful make targets:

make clean
make patch  # Generates the patched bin at build/internal_flash_patched.bin, but doesn't flash
make flash_stock_int
make flash_stock_ext
make flash_patch_int

TODO

• Figure out safe place in RAM to store global/static variables. The current configuration described in the linker file is unsafe, but currently we have no global/static variables.
• Maybe slim external flash ROM (remove easter eggs, ROMs, etc) to make room for more homebrew.

Development

Main stages to developing a feature:

1. Find a place to take control in the stock rom (usually function calls).
2. Add the stock function and its address to Core/Inc/stock_firmware.h.
3. Implement your own function, possibly in Core/Src/main.c. There's a good chance your custom function will call the function in (2). You will also probably have to add -Wl,--undefined=my_custom_function to LDFLAGS in the Makefile so that it doesn't get optimized out as unreachable code.
4. Add a patch definition to patches/patches.py.

Journal

This is my first time ever developing patches for a closed source binary. I documented my journey in hopes that it helps other people. If you have any recommendations, tips, tricks, or anything like that, please leave a github issue and I'll update the documentation!