"Real" USB Host Mode

udoschneider · Post by **udoschneider** » 21 Jul 2022, 12:24

All,

as far as I can see the micro-USB front connector provides a "kind-of" USB Hostmode to provide access to the eMMC.

Is it also possible to use this as a full blown USB host-mode connector on Linux? E.g. provide custom serial/hid devices via Gadget API/ConfigFS?

Best Regards,

Udo

nicolaiB · Post by **nicolaiB** » 21 Jul 2022, 14:44

Hi Udo,

It depends.

The Raspberry Pi Compute Module only has one internal USB port which can be eigher used in host or device mode. Therefore it's not possible to use both modes at the same time. In the hardware design of the RevPi we use a switch which is triggered by the USB voltage (VUSB) on the micro USB port. If VUSB voltage is present, the micro usb port is connected to the interal USB port and if not it will be connected to the USB hub. As things like the ethernet interface(s) (Core, Connect, Compact) and UARTs (RevPi Connect, used for RS485 and ConBridge) are connected to the USB hub, it is not possible to use the device in gadget mode if any of this interfaces is required.

Hope this helps.

Nicolai

udoschneider · Post by **udoschneider** » 22 Jul 2022, 10:47

Hi Nicolai,

nicolaiB wrote: ↑21 Jul 2022, 14:44 It depends.
[...]
Hope this helps.

Thanks a lot for your answer. If you switch between modes based on VUSB from the micro USB port I finally understand why all my experiments failed.
This doesn't help with my project (have to search for other HR now

) - but at least I know for sure now - so it doesn help.

Again, thanks for your help!

Best Regards,

Udo

nicolaiB · Post by **nicolaiB** » 22 Jul 2022, 18:22

With the current CM / CM3 / CM4S based devices we don't have any other options than switching the only USB port. With CM4 based devices like the upcoming Connect 4 this will be hopefully history. The CM4 has an internal USB2 controller which will be used for otg and a Usb3 controller which is attached to the pcie port.

Nicolai