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dnv32 edited this page Feb 15, 2023 · 2 revisions

Introduction

USB-Cereal is an open-source project originated at Google. This USB-Cereal fork by 0xDA is an effort to make USB-Cereal devices available for purchase for developers. A few notes on USB-Cereal compatibility:

  • It requires serial TX/RX lines brought out into SBU1/2 pins.
  • USB-Cereal is made compatible with both 1.8V and 3.3V signaling.

Quick Reference Diagrams

Block Diagram Annotations

Getting Started

  1. Important: First and foremost, USB-Cereal is only compatible with the devices that have been designed for it. Do not try to attach USB-Cereal to any random device, it can potentially damage the device.
  2. Set the voltage reference to a correct voltage appropriate for the device under test.
  3. Attach USB-Cereal to the DUT with the correct orientation. USB-C natively implements pin flip capability that makes it orientation agnostic, and this is not the case for USB-Cereal - there is only one correct orientation!
  4. Connect USB-Cereal with the USB-C to A or USB-C to C cable to the PC. At this stage, we are connecting to the USB-Cereal's port marked "debug". It is the port that is routed to the internal FTDI232RQ IC and that presents serial communication as USB packets.
  5. You should see both orange and yellow LEDs light up on USB-Cereal.
  6. Open your favorite Serial monitor and attach it to the port corresponding to USB-Cereal.
  7. If everything is working properly, you should now see the logs coming from the DUT, and also should be able to send characters from PC to the DUT.

USB-Cereal Applicability Limitations

As USB-Cereal is using SBU pins that are generally used for auxiliary applications, it is challenging to make it compatible with USB-C DUTs that do use SBU pins. An example of such a device can be USB 3.2 Alt Mode Display Port-capable hardware.

Note: For such devices it is still possible to make use of USB-Cereal by using an additional multiplexer IC, and a way of switching the multiplexer from alt. mode application lane to UART lane.

USB-Cereal Open Source Files

ECAD files are drawn in Altium Designer. MCAD STEP file assembly (Designed in AutoCAD Fusion 360).

Both the original design from Google and the OxDA forks are licensed under very permissive Apache 2.0 License.

Thanks and Attributions

Thanks to Google for supporting and releasing the original work: github

Thanks to Kevin Balke (instagram, github) for brewing up the most awesome logo for the project!

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