On the Raspberry PI, USB is tied directly to a hub, so there’s no way ( I’ve heard of ), to run it in ‘gadget or peripheral’ mode, even though the CPU does support device mode. Will the X15 have this issue?
It appears that the USB3.0 port goes directly to the hub, so we will not be able to use it as a gadget. However, it does look like the we can use one or two of the USB2.0 ports as gadget/peripheral ports.
The processor looks like it has support, but the BBX15 would need to be able to disconnect the cpu from the USB 3.0 HUB. If it doesn’t have a way then you are stuck with host mode only on the 3.0 Port.