A software engineer and YouTuber known as bitluni has built a functioning graphics processing unit from 8,192 individual RISC-V microcontrollers, producing a homebrew GPU that draws more than 2,000 watts of power and requires a separate 3D-printed enclosure to program.
The six-month project, undertaken in partnership with PCB design software firm Altium, uses CH570 RISC-V microcontrollers purchased directly from the manufacturer at US$0.13 (approximately £0.10) each. An additional 256 larger chips with floating-point units coordinate the swarm of smaller processors. The result is a GPU capable of driving a QVGA display at 320×200 resolution using individually addressable RGB LEDs per microcontroller.
“It was my nemesis,” bitluni said of the project. “The clusters I made before were already challenging my sanity. I thought I was done with the topic, but the budget and these tools would allow for a cluster of a different magnitude, and the magnitude I had in mind was just insane.”
Engineering Obstacles
The PCB design presented immediate difficulties. The six-layer board was laid out as 32 rows of 32 chips, each row forming a “blade.” The PCB manufacturer’s ordering system could not process a board of this complexity, requiring each blade to be split into two pieces and assembled separately.
When the first test boards arrived, several microcontrollers were defective or intermittent, requiring a complete redesign to relocate signal traces and eliminate interference. On the replacement boards, bitluni discovered that the MOSI and MISO data lines had been crossed, routing input signals to the output channel and vice versa.
“No matter how hard you try, you will get rx and tx wrong on the first try,” he noted.
The final working cluster draws over 2,000 watts of power. Programming the device requires a 3D-printed fixture to align the multiple programming headers, a detail the Tom’s Hardware article described as requiring “a 3D printer to program.”
Open Source and Next Steps
Bitluni plans to release all design files as open source, allowing anyone to replicate or improve the build. He has not yet published performance benchmarks but expects to release a follow-up demonstration video.
A second version is already in development, targeting roughly 32,000 microcontrollers, approximately four times the scale of the current build. If successful, it would represent one of the largest homebrew processor arrays ever constructed.
Sources: Modder builds 8,192-core GPU at home out of RISC-V microcontrollers (Tom’s Hardware, July 7); Madlad builds homebrew GPU using 8,192 RISC-V chips (The Register, July 6)