The new mod, which reprograms the onboard STM32 chip, is still in the experimental stage.
Some clever detective work has laid the groundwork for homebrew game development for Nintendo’s retro throwback machine.
Your Favorite Retro Games on the Nintendo Game and Watch
YouTuber stacksmashing has released a series of videos on how to hack the Nintendo Game and Watch. It’s not a simple process, but so far, NES and Game Boy emulation is running in a basic state, alongside an obligatory Doom port.
This hack is possible due to the electronics the Nintendo Game and Watch uses. The STM32H7B0 is part of the widely used STM32 family of chips. These chips can be found in many hobby microcontroller boards and can be read and modified via debug pins on the chipset. The chip is paired with a 1MB SPI Flash chip, which also can be used to gather data about what is going on in the main processor.
Fortuitously, The PCB of the Nintendo Game and Watch exposes all the pins required for reprogramming the STM32 chip as pin headers. However, accessing the firmware of the chip turned out to be difficult, as Nintendo had set production flags stopping direct reading of the chip – a security feature of the STM32.
Hardware Detective Work Pays Off
No access to the firmware makes it hard to run custom ROMs on the hardware, but stacksmashing still had access to the RAM of the chip and the separate SPI Flash chip. Using data collected from RAM and SPI Flash, he was able to work out what encryption was used for loading ROMs, eventually modifying it to run a hacked version of Mario Bros.
The next task was to find a way to dump the Nintendo firmware from the chip so it could be backed up. Without this step, any attempt to reprogram the device normally might cause it to stop working permanently, “bricking” the console.
After teaming up with Konrad Beckmann, a hardware hacker from Sweden, they found that by running a piece of custom code from the SPI Flash chip, they were able to offload the whole firmware for the Nintendo Game and Watch.
Now everything was in place to hack to their heart’s content, knowing that they could revert their changes at any time. Konrad Beckmann wasted no time putting the new freedom to good use on Twitter:
From here, after an incredible amount of hard work, custom emulators started to take shape. Current efforts are focused on making an easy to use homebrew setup for the Nintendo Game and Watch.
While still in its early stages, the homebrew Nintendo Game and Watch code and instructions can be found on stacksmashing’s GitHub page.
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