The Sega Dreamcast was a really quirky console and while it was underappreciated when it was available, with relatively poor sales, it has garnered a substantial cult following since Sega discontinued the consoles in 2001. One of its most interesting features was the Virtual Memory Unit (VMU), which was a memory card packaged in a module with its own tiny LCD and buttons. It had some interesting capabilities, including supporting some minigames all on its own, separately from the Dreamcast console. DynaMight dramatically expanded on that by making a VMU capable of running “real” games, including Doom.
To enable its unique functionality, Sega gave the VMU a CPU and RAM of its own. But that was extremely limited—almost any pocket calculator available today will have more power. There is no chance that a VMU could run anything beyond the kinds of simplistic minigames it was designed for, which is why DynaMight had to replace all of that. They are, essentially, using the VMU shell and buttons for modern hardware that has a lot more processing power and RAM.
That hardware is an ESP32-WROVER-E N4R8 microcontroller. For a microcontroller, that is quite powerful. It has an Xtensa dual-core 32-bit LX6 processor that can run at 240MHz and 520KB of SRAM, plus an additional 8MB of PSRAM connected through quad SPI. DynaMight paired that with a full-color 1.69” IPS display and a tiny speaker. Those components go on a custom PCB with integrated button pads. Power comes from a 600mAh lithium battery.
DynaMight designed the PCB to fit into a VMU shell, but it isn’t a simple drop-in replacement. Some modification of the VMU shell is necessary to make room — mostly trimming the internal ribs that provide structural support. A simple 3D-printable spacer helps to support the display after making those modifications.
To run games, DynaMight selected Retro-Go. That is firmware built for ESP32 microcontrollers to run emulators for several systems, including the NES, SNES, Game Boy, Game Boy Color, Sega Genesis, Sega Game Gear, Colecovision, and Atari Lynx. Retro-Go has a lot of optimization tricks under the hood to help run those emulators on the relatively low-spec hardware.
And, best of all, Retro-Go supports Doom and that means DynaMight was able to accomplish the traditional feat of running Doom on their device. DynaMight says that actually playing games on the VMU isn’t very comfortable, due to its small size, but this is still a very cool project.