USB Cereal is an open-source hardware USB-C debugging & development tool (Crowdfunding)

0xDA LLC’s USB Cereal is an open-source hardware development tool with three USB-C ports designed to simplify the testing, development, debugging, and manufacturing of devices with USB Type-C ports.

Initially originated at Google, the USB Cereal project has gone through multiple revisions to optimize its quality and lower the BoM cost, and the device can be used for all sorts of USB Type-C debugging using a UART serial communication with the host device through the USB-C sideband use (SBU) pins typically reserved for device-specific applications.

USB-C debug board

USB Cereal specifications:

  • USB Type-C ports
    • 2x USB-C ports for passthrough between the host and device under test (DUT)
      • Note: the DUT port is on the side with a single USB Type-C connector
      • No orientation detection has been implemented to keep the design as simple and inexpensive as possible
    • 1x USB-C port for capture support to 3 Mbps connected through FTDI FT232RNQ USB to TTL chip (CP2102N can also be used as a substitute). No auto-level detection in order to support more exotic devices that may not be fully UART compliant
  • Misc
    • Switch to select between 3.3V and 1.8V signal levels
    • Green and Orange LEDs to monitor Tx and Rx operations
  • Dimensions – Small and portable USB Cereal connected to DUT

The DUT does not need any specific USB drivers so the capture can work on all types of hardware. We are told there’s also no need to open up the DUT, add jumper wires, or extra connectors, simply connecting the USB-C “DUT” port from the USB Cereal is enough.

Autodesk ECAD and MCAD files, as well as the PDF schematics, can be found on GitHub. What we are not shown is a program used to capture and analyze the data over serial and its use cases were not immediately clear to me. But Dmitrii Votintcev (acting as 0xDA LLC) says that USB-Cereal does not duplicate any functionality of Twinkie, and it only focuses on one thing: USB-C serial communication over SBU pins.

USB Cereal vs Tag Connect vs Suzy Q vs MicroArt

We are also shown a comparison table with USB Cereal, Tag-Connect, Suzy-Q, and uArt. So if I understand that right, the device is more like a USB to TLL debug board that also enables USB passthrough and relies on the SBU1/SBU2 pins of the USB interface instead of a separate header. I’m still slightly confused since the DUT’s firmware would have to be updated to send/receive data over those pins.

The USB Cereal has just launched on Crowd Supply with a $10,000 funding goal. A $49 pledge is asked for the debug tool with free shipping to the US and an extra $8 for shipping to the rest of the world. Delivery is scheduled to start around mid-July 2023.

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16 Comments
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andelf
andelf
1 year ago

$49 for a serial port adapter that can only handle usb-cvdevices? Wat. Why not add 4pin serial connector too? I wouldn’t call a serial port a “debugging tool” I assumed it would implement jtag/swd too..
I like the 1.8/3.3volt switch, though

0xDA
0xDA
1 year ago

Thank you for your overview of the project, and thank you for the notes as to what is not clear on the campaign page, we will make sure to include the usage examples in future campaign updates. To answer a few points: What we are not shown is a program used to capture and analyze the data over serial Any serial console port tools could work here. On Linux screen is an option. On Windows TeraTerm/xTerm and such work well. the device is more like a USB to TLL debug board that also enables USB passthrough and relies on the… Read more »

0xDA
0xDA
1 year ago

Exactly! We choose to be a USB-C exclusive interface as one can buy an FTDI cable (or similar) with all kind of jumper interfaces for a few bucks. The intent here is really to target devices that are manufactured at larger scales than a few dozen, and are worked on by many developers.

repkid
repkid
1 year ago

cool tool but looking at the schematic on github the debug usb-c connector isn’t spec compliant: each cc pin should have an individual resistor rather than being ganged together. the raspberry pi 4 also made this mistake.

0xDA
0xDA
1 year ago

Hey repkid, thank you for noticing that, there was a history with this mishap when the device was first released, it has been fixed and tested. Will push the updated design files in a bit!

0xDA
0xDA
1 year ago

The repo is updated with newer designs, and the design with this mistake is deprecated.

repkid
repkid
1 year ago

Good luck with the campaign!

Tired_
Tired_
1 year ago

So this will perform the functions of the impossible-to-buy SuzyQable?

0xDA
0xDA
1 year ago

No, SuzyQ uses a different approach (implementing a second USB interface over SBU pins, and a cable detection scheme). USB-Cereal gives exclusive priority to UART over SBU pins.

Tired_
Tired_
1 year ago

Kinda misleading to have it in the chart with SuzyQ like that, isn’t it? I bet more than one person will buy this, thinking they can fix their Chromebook.

0xDA
0xDA
1 year ago

Added a clarifying note to the table – thanks for bring this up!

T-C
T-C
1 year ago

Can test PD?

Willy
1 year ago

I’m sorry but I completely failed to understand what this device was trying to do, both from its description and from its specs, I thought it was trying to capture USB traffic and send it to another port. That’s finally by looking at this diagram that I understood: https://github.com/oxda/usb-cereal/blob/main/docs/usb-cereal-cp-schematics.pdf For those who, like me, were left in doubt, it embeds a CP2102 USB-to-UART controller that’s connected to pins SBU1/SBU2 of the device under test on one side, and to one of the two USB-C connectors on the other side. So it’s like a cable between a device and a host,… Read more »

0xDA
0xDA
1 year ago

Exactly – apologies for not making it clear from the article, will try to add a block diagram to make it a bit more visual.

There are devices on the market that use this strategy, but the big goal here is to promote the strategy for future devices.

Khadas VIM4 SBC