On the 4th of March 1999, Bandai released the WonderSwan in Japan. It had been developed and supervised by Gunpei Yokoi up until his tragic death in 1997, and was set to compete with the other console that he designed earlier while working at Nintendo, the Game Boy. Sadly, the WonderSwan turned to be a commercial failure, only managing to obtain a small portion of the Japanese handheld market before being completely crushed by the Game Boy Advance later on, without ever seeing an official release overseas. However, its memory still lives on in many enthusiast's hearts, whether it is in appreciation of the legendary game designer's legacy or due to its niche yet quality games.
20 years after release, a breakthrough has been made by furrtek in an effort aimed towards game preservation and better emulation: the WonnderSwan's bootrom has finally been dumped. This has been possible thanks to a hardware-based attack which glitches the CPU to trick the console into booting up without clearing the memory region containing the bootrom; a method very similar to the one used years earlier with the Game Boy Color. Still, the journey wasn't an easy one, as it was filled with many non-trivial platform-specific hurdles: for example, the original approach overclocks the CPU repeatedly and in short bursts to make it skip the memory clearing instruction, however, the WonderSwan's CPU has a much higher frequency tolerance than the Game Boy's. Nevertheless, thanks to an FPGA, custom code, experience and a lot of patience, furrtek has managed to dump both the original model and the WonderSwan Color's bootroms, and everything has been documented in a post linked in the sources below! (in French)
Now, you may be asking yourself: "This is cool and all, but what does this mean for me as a retrogamer aside from seeing a fancy boot screen?". byuu, the creator of bsnes and higan, has stepped forward to answer the question: the WonderSwan's bootrom also contains a settings menu which lets a player store his/her own personal info such as the name, birthday, gender and blood type. This data can later be used by games to do all sorts of things, like triggering easter eggs or automatically filling a character's name with your own. Now that the bootrom has been dumped, this feature can finally be configured and emulated properly!
byuu's post (NOTE: the WonderSwan Color's bootrom has since been dumped) said:Courtesy of furrtek, we now have the WonderSwan boot ROM extracted and emulated! furrtek was able to achieve this via clock glitching the original hardware during boot-up and then extracting the ROM via serial. WonderSwan Color is next up.
The reason this is important is not just the boot screen logo. If you hold down the start button during startup, the WonderSwan boots into a settings menu where you can configure your name, birth date, gender, and blood type. For the last one, remember this is Japan. In Japan, blood types are roughly analogous to the west and horoscopes.
Your settings are stored on an internal EEPROM (memory chip), which WonderSwan games can then read back to customize the game for you: pre-filling in your name, providing easter eggs, etc. Some cartridges further provide a real-time clock, which can trigger events on your birthday.
With the boot ROM now dumped and emulated, these settings can now be configured via emulation.
Starting from version 106.197, Higan has implemented support for the newly dumped bootroms. You can see a video of it in action below:
If you want to try it yourself, you can download Higan's latest nightly builds here. WonderSwan bootrom dumps contain copyrighted content and cannot be linked to on GBAtemp, so you will need to obtain one yourself (hashes for verification can be found here).
Source 1 (furrtek's post)
Source 2 (byuu's blog)