For some E7500 boards with 5 USB connectors, only 4 of them are legacy supported: 2 in the back (USB0 and USB1), and 2 FUSBs (Front USB-FUSB0 and FUSB1 or USB2 and USB3 respectively). The fifth one (USB4) is not, this means you cannot use any USB device that is connected to this connector under DOS, but you still can use it inside the OS.