Cynthion is an all-in-one tool for building, testing, monitoring, and experimenting with USB devices. Built around a unique FPGA-based architecture, Cynthion’s digital hardware can be fully customized to suit the application at hand. As a result, it can act as a no-compromise High-Speed USB protocol analyzer, a USB-hacking multi-tool, or a USB development platform.

Out-of-the-box, Cynthion acts as a USB protocol analyzer capable of capturing and analyzing traffic between a host and any Low-, Full-, or High-Speed ("USB 2.0") USB device. It works seamlessly with our open-source analysis software.

Combined with our LUNA gateware and Facedancer libraries, Cynthion becomes a versatile USB-hacking and development tool. Facedancer makes it quick and easy to create or tamper with real USB devices—not just emulations—even if you don’t have experience with digital-hardware design, HDL, or FPGA architecture!

For more information, see the Cynthion Crowd Supply page.

This project is broken down into several directories:

• docs/ -- sources for the Cynthion Sphinx documentation
• cynthion/python/ -- sources for the main cynthion python module and amaranth gateware.
• cynthion/rust/ -- sources for the main cynthion rust crate.
• firmware/ -- sources for Cynthion firmware.
• shared/ -- a collection of toml files containing values shared between host code, gateware and firmware.
• util/ -- miscellaneous support files for Cynthion

Cynthion's documentation is captured on Read the Docs. Raw documentation sources are in the docs/ folder.

Cynthion is supported by two additional firmware projects:

• Apollo, the firmware that runs on Cynthion's debug controller, and which is responsible for configuring its FPGA.
• Saturn-V, a DFU bootloader created for Cynthion.