This MCU-Based Cyberdeck Boots in a Couple of Seconds
Instead of the usual Raspberry Pi single-board computer, Abe’s cyberdeck-like mini computer works using microcontrollers.
When building a cyberdeck, pocket PC, or anything similar, the natural choice is to use a single-board computer (SBC) like those Raspberry Pi became famous for making. They’re relatively compact, but give you a legitimate computer capable of running a real desktop operating system and all the associated software. But those operating systems are slow to boot and those SBCs consume quite a lot of power. To avoid those disadvantages, Abe used an MCU as the “brain” of his DIY mini computer that boots in seconds.
A microcontroller unit (MCU) is kind of like a computer, except not really at all. Microcontrollers contain processors, memory, and storage, just like computers. But they usually have very little of each. That trade-off is worthwhile, because you can work closer to “the metal” and interact directly with other hardware, like sensors. Microcontrollers don’t usually run operating systems (which have layers of abstraction piled on) and instead run firmware that has direct access to the hardware, including I/O pins and communications interfaces.
However, those lines between “operating system” and “firmware” can get quite blurry. In fact, you can run (usually old and lightweight) operating systems on microcontrollers. In this case, Abe created firmware called slime_os based on MicroPython and it includes an app-launcher feature. Apps are self-contained packages and the firmware can load them up on demand. In that way, it is a bit like an RTOS).
This is all possible because Abe used a special microcontroller — actually two of them. The mini computer has a Pimoroni PicoVision, which contains both a Raspberry Pi Pico W development board (which, itself, contains a Raspberry Pi RP2040 MCU) and an additional RP2040 MCU. The first acts as CPU, while the second acts as GPU for rendering video output through an HDMI port. The PicoVision also has neat features like line-out audio, buttons, and a microSD card slot. Abe built his slime_os on top of firmware designed for the PicoVision.
Other hardware in Abe’s mini computer includes a mini keyboard connected via a third RP2040 on an Adafruit Trinkey QT2040 development board, a lithium battery, an Adafruit USB charger, and an Elecrow 5” touchscreen LCD. Those fit inside the 3D-printed enclosure.
Abe even designed an expansion system. The little expansion cartridges contain microcontrollers of their own, which can communicate with the main CPU microcontroller to add new functionality. Abe built the demo expansion cartridge around a Seeed Studio XIAO SAMD21 development board, but they can be made with any dev board/MCU.
The mini computer’s design files aren’t available right now, but Abe did release slime_os on GitHub for anyone with a PicoVision that wants to try it.
