The mini-USB type-A OTG/device
client-mode socket is multi-functional. In addition to providing an alternative source of power, it gives access to an on-board front-end two-port USB client-side hub. (This is not related to the separate
host-mode USB socket described later). One port of the hub goes directly to the
USB0 port of the TI AM3358/9 SoC, while the other port connects to a dual-port
FTDI FT2232H USB-to-serial converter to provide board-to-external-host serial communications and/or JTAG debugging. The BeagleBone's Linux serial console is available through this USB serial connection.
The SoC's
USB0 connection to the front-end hub works in one of two modes, and you can toggle between them at any time: it either presents the SD card as a mountable USB storage device to the host, or it provides an
Ethernet-over-USB networking interface which yields a simple method of quick-start. The Ethernet-over-USB facility is additional to the BeagleBone's normal 10/100 Ethernet interface, which is directly implemented in the SoC rather than hanging off USB as in some other designs. Full IPv4 and IPv6 networking is provided by the supplied Linux system out of the box.
In addition to the USB OTG Device or
client-mode facilities already described, BeagleBone also provides one
host-mode USB type-A socket on the other end of the board. This is driven from the
USB1 connection on the AM3358/9 SoC, and provides access to USB host peripherals such as mice, keyboards, storage, and wifi or Bluetooth dongles, or a USB hub for further expansion.