USB-Cereal

USB-Cereal is an open-source USB-C debug tool that gives you UART serial access through the sideband (SBU) pins of a standard USB-C connector, with no exposed pads, no debug headers, and no disassembly required. It sits inline between your device and your workstation: one port connects to the device under test, a pass-through port keeps your normal USB connection live, and the debug port presents a standard virtual COM port to the host via an FTDI FT232RNQ or CP2102N bridge. Open any serial terminal and you're reading logs immediately.

What makes USB-Cereal genuinely different from a standard USB-to-UART adapter is where the serial signal comes from. Because it taps the SBU sideband pins rather than the USB data lines, it works completely independently of the USB stack. That means you get serial output from the very first instruction your processor executes, including bootloader stages and early kernel bringup where USB-based logging simply isn't available yet.

A manual slide switch selects 1.8 V or 3.3 V signaling to match your target hardware, and the intentional absence of auto-detection means it also works with non-standard or partial UART implementations. TX and RX activity are visible on dedicated onboard LEDs. Standard FTDI and Silicon Labs drivers are supported natively across Linux, macOS, and Windows, with no custom tooling required on the host side.

If your device has a USB-C port and routes UART to the SBU pins, USB-Cereal is the cleanest way to get serial access to it.