Interfacing (DSI, CSI, I2C, etc.) • Re: USB Gadget Mode via USB-C (RPI 4B)

Thank you very much for the helpful questions and hints!
And sorry for the lacking information considering my setup.

We don't know which of the two connectors on that cable (the USB A or USB C) has the data pins connected. If the data pins are on the USB C leg it won't work as shown. If they're on both legs that violates the USB spec and likely won't work either.

The Y-cable has its data pins only connected to its USB A side and pwr on both.

1. You have two separate PSUs feeding into your Pi: the Laptop and whatever is on GPIO/USB C. Unless those output identical voltages (after any voltage drop in the cables) one of them will be trying to back feed power into the other. Sometimes that appears OK, sometimes it doesn't work.
   The safe fix is to cut the power wire in the cable(s) between USB host and the Pi.
   Alternatives include:
   1. Roll your own from A USB A male breakout, a USB female breakout and some header pins.
   2. Buy a suitable commercial adapter that does the job. (I use these)**
   3. Try a Y cable at the PC end with a single USB connector at the Pi end and no separate PSU.
2. Have you tested those adapters with another device on the end the Pi is currently connected to?

Nice! So back powering might very well be the issue here, I'll cut the power of one of my A to C cables and report back. I'll also try to get some of these nice 8086 adapters (:

Statistics: Posted by fl0w — Mon Aug 25, 2025 2:10 pm

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