Number #3, indicated by USB Power, is also used for gadget mode: with this connection, a host laptop, for example, can see the board as a gadget, and with this, plenty of things can happen: it can be used as a mass storage stick for example, or one can use the rockchip rkdeveloptool to reflash media on the board. The inner workings of the USB 3.0 are as follows: there is the DesignWare Core Dual Role Device (DRD) which can work both in host and gadget mode, and both in USB 2.0 and USB 3.0 modes. One is the same that is used for the USB 2.0 host controller (the Inno phy) and the new one is the USB 3.0 USBDP PHY (combo with DisplayPort Alt mode).