Compute Module • Re: Help with CM4 USB DFU

Sounds very much like a signal integrity issue. USB keyboard etc will almost certainly be using USB 1.1 so 12Mbits . Where as when you are trying to connect to the computer you will be running at 480Mbits. Are are the traces and wiring 90R different pairs with no stubs ? You refer to "Paralleling" if you have two connectors in Parallel that creates a stub and will almost certainly corrupt fast signals.

Thanks for getting back to me so quickly That's a very good point, thank you. I'll check with the hardware guys and get back to you.

Hi again,

The PCB layout showed a pretty big stub on the main PCB where the signal lines split off between the on-board USB-C connector and the bulkhead connector - isolating this at the start of the stub seems to have allowed USB DFU to work over the USB-C connector, which is great progress so thank you very much for your help.

We're going to have to re-think USB DFU from outside the pressure vessel as the subsea connectors and cables that we are using are not twisted or shielded and are a fair length, so seem to be suitable for low speeds as you said, but probably not good for 480Mbps. We'll probably keep the USB-C connector on the PCB for DFU only (useful for flashing CM4s without an IO board and for reducing wear on the board-mount connectors) and implement a USB MUX IC on-board to separate this from the bulkhead USB lines, similar to the CM4 IO board.

Many thanks,

Adam

Statistics: Posted by AdamWTracerco — Tue Apr 29, 2025 2:44 pm

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