USB-C Gadget mode about nerves_system_rpi4 HOT 7 CLOSED

I agree - it looked possible when I was doing the original port. I wasn't sure about power, but I guess it doesn't hurt to try.

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I imagine it should work on decently powerful laptops, blog post sure makes it look like it works. I'm guessing it can negotiate something more juicy than the ol' micro-USB gadgets could.

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I tried, as an experiment, to emulate a USB HID device (keyboard) on Nerves Rpi4 by following the indications in this post, originally written for the Zero on Raspbian and basically similar to the post linked above.

I loaded the dwc2 and libcomposite modules, and had to manually mount ConfigFS with mount none /sys/kernel/config -t configfs. Still, the problem is that ls /sys/class/udc gives empty results, so something is clearly missing but I don't know what.

Any idea about what would be needed to get that to work?

I see other efforts to get ConfigFS to work on some Pi models, like nerves-project/nerves_system_rpi0#62

It would be really great to be able to use the Rpi4 USB-C in device mode.

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An update to this, I managed to fix this issue by adding the dwc2 device tree with a custom fwup.conf like it's done here on the RPi Zero: https://github.com/nerves-project/nerves_system_rpi0/blob/master/fwup.conf#L229

Now the USB Device Controller is properly populated in /sys/class/udc and the /dev/hidg0 device appears (and is recognized by my laptop, to which the RPi4 is connected via USB-C). The problem is that, when I try to write HID reports to /dev/hidg0, the write operation hangs. Any idea?

I'd be very happy to share my proof-of-concept if I get it to work end to end.

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I figured it out, the HID report description was wrong. Now it works fine.

Here is a (hacky but working) proof of concept of the RPi4 on standard Nerves using the USB-C in gadget mode (emulating a USB Keyboard): https://github.com/lucaong/nerves_rpi4_hid_gadget_poc

Ideally one would use nerves/usb_gadget instead of the custom shell script to create and setup the USB gadget.

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So this would make it pretty likely that we could do the ethernet gadget or whatever the pi0 does to provide SSH over the wire by default?

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That definitely sounds possible. In my experiments with using the USB-C port in gadget mode, plugging it to a laptop is enough to power the Pi.

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