OK bad news, using the standard micro USB cable, my always-useful Female-Female adapter, and an 8GB USB key, I installed and ran "usbcontrol" from the repositories and the mode wouldn't switch from "b_idle" to "host" at all. Trying the old "echo host > /sys/.../musb_hdrc/mode" had the same result. Whatever you write, it is overwritten with "b_idle"...