Fomu is a programmable FPGA development board small enough to plug directly into a USB Type-A port. It can run a RISC-V soft CPU or be reconfigured with other hardware designs, making it a compact way to experiment with FPGA development. Its main compromise is equally important: Fomu has no GPIO, so it is not designed for connecting a large assortment of external sensors and devices.
What Fomu is—and what “fits in your USB port” means
Fomu is a tiny FPGA board, not a conventional USB peripheral with one fixed purpose. The FPGA can be configured to implement different digital hardware designs, including a soft processor. The project describes its default firmware as exposing a USB bootloader that runs a RISC-V softcore. The phrase “fits in your USB port” refers to a USB Type-A connection; it should not be taken to mean the board plugs directly into USB-C.
For readers asking, “What can I do with an FPGA that plugs into a USB port?” the short answer is: learn how programmable logic works, experiment with hardware designs, and explore a soft processor in a very small, self-contained format. Fomu’s convenience is physical. It does not give it the broad expansion options of a larger development board.
Fomu hardware specifications
Crowd Supply lists these production-board specifications. The distinction between FPGA memory and memory assigned to a soft CPU matters: the listed 128 kB is RAM for a soft CPU, not a general claim that the FPGA itself contains that amount of RAM.
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- 4332 Fomu - ICE40 FPGA Development Board
| Feature | Listed specification |
|---|---|
| FPGA | Lattice ICE40UP5K |
| External oscillator | 48 MHz |
| Soft-CPU RAM | 128 kB |
| SPI flash | At least 1 MB |
| USB | USB 2.0 full-speed (12 Mbps) |
| Other on-board features | Four copper pads and one RGB LED |
The four pads are physical features, but Crowd Supply says capacitive-touch solutions for them had not been validated. They should not be described as confirmed touch buttons.
What you can do with Fomu
Learn FPGA design
Fomu is intended for learning and experimenting with FPGA hardware. An FPGA is reconfigurable: instead of being limited to a single fixed circuit, it can be loaded with a design that describes the logic you want it to implement. The Fomu hardware repository documents the iCE40UP5K board and an open Verilog-to-bitstream toolchain.
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- Package Introduction: 1pc*【FPGA and PMOD-SDCARD】
- ICE40UP5k main chip, 5280 LUT/128KB SPRAM/PLL/ SPI/I2C/DSP/PWM
- On-board iCELink debugger, supporting drag-and-drop programming, USB CDC serial port and JTAG
- Lead out all the IO with standard PMOD connector and can connect with other PMOD devices
- Totally use open source tool chain to develop
Explore a soft processor
A soft CPU is a processor implemented in the FPGA’s programmable logic rather than supplied as a separate fixed CPU chip. Fomu’s default firmware is described as providing a USB bootloader running a RISC-V softcore, and the listed 128 kB of RAM is allocated to a soft CPU. This makes the board relevant to both digital-logic experiments and small processor-oriented projects.
Use an open-source toolchain
“Open toolchain” refers to the software flow, not to an absence of setup. The project identifies Yosys, IceStorm, and nextpnr as part of its open-source development ecosystem and describes loading code over USB. A host computer with a USB port is required; the workshop documentation also notes that Linux users may need elevated permissions or udev rules.
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- Package Introduction: 1pc*【FPGA and PMOD Pack-1】
- ICE40UP5k main chip, 5280 LUT/128KB SPRAM/PLL/ SPI/I2C/DSP/PWM
- On-board iCELink debugger, supporting drag-and-drop programming, USB CDC serial port and JTAG
- Lead out all the IO with standard PMOD connector and can connect with other PMOD devices
- Totally use open source tool chain to develop
The main limitation: no GPIO
Crowd Supply’s comparison lists Fomu as having no GPIO. That makes it a poor fit if your plan depends on wiring many external sensors, buttons, displays, or actuators to exposed pins. Its appeal is a compact board for on-board and USB-connected FPGA experimentation, not a general-purpose breakout platform.
The official comparison names ICEBreaker and TinyFPGA BX as alternatives with GPIO. When comparing them, consider exposed I/O, the USB form factor, whether a case is included, available input and output controls, and the intended workflow—not just board size.
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- Package Introduction: 1pc*【FPGA and PMOD-LED】
- ICE40UP5k main chip, 5280 LUT/128KB SPRAM/PLL/ SPI/I2C/DSP/PWM
- On-board iCELink debugger, supporting drag-and-drop programming, USB CDC serial port and JTAG
- Lead out all the IO with standard PMOD connector and can connect with other PMOD devices
- Totally use open source tool chain to develop
Production and Hacker revisions
Fomu has distinct production and Hacker revisions. The workshop documentation says boards ordered through Crowd Supply are the production version and includes material for identifying the models. If following instructions or using hardware examples, check which revision you have rather than assuming every Fomu board is identical.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Availability and project history
Crowd Supply’s listing showed Fomu as in stock when checked for this article, but stock status can change; confirm the current Fomu FPGA board listing before making a purchase decision. The same page reports that the campaign funded on February 2, 2019, with 1,039 backers and $88,032 raised against a $10,000 goal. Those are historical campaign figures, not present-day sales or availability data.
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- Package Introduction: 1pc*【FPGA and PMOD-Switch】
- ICE40UP5k main chip, 5280 LUT/128KB SPRAM/PLL/ SPI/I2C/DSP/PWM
- On-board iCELink debugger, supporting drag-and-drop programming, USB CDC serial port and JTAG
- Lead out all the IO with standard PMOD connector and can connect with other PMOD devices
- Totally use open source tool chain to develop
In a June 7, 2019 production update, project update author Sean “xobs” Cross wrote: “Now that the hardware is mostly finished, we can turn our attention to software and tooling.” This was a statement about the project at that point in its development, not a description of the current state of its software.
Crowd Supply introduced Qomu in a March 18, 2021 update as a later related device developed with QuickLogic. Qomu is a separate product, not another name for Fomu.
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