USB OTG Gadget (Peripheral) Mode
You can make Allwinner devices emulate various USB peripherals using the Linux USB gadget drivers. There are drivers for emulating serial ports, network interfaces, storage devices, video and audio devices, etc.
It's possible to emulate multiple devices at once, so when you connect your device to the PC's USB port, you'll see a new network interface, get access to the serial console on the device over USB and also be able to export the SD/eMMC as two USB storage devices to the PC.
The above is an extreme example.
The USB gadget device setup can be done via configfs by creating directories and manipulating files.
Here's a script that I use to emulate a USB mass storage device and the network link between the device and the host.
cd /sys/kernel/config/usb_gadget/ # Create a new gadget: mkdir g1 cd g1 # Setup identifying information for the USB bus for our emulated # USB device as a whole: echo 0x1d6b > idVendor echo 0x2000 > idProduct mkdir strings/0x409 echo "11111111111" > strings/0x409/serialnumber echo "megous.com" > strings/0x409/manufacturer echo "Oranbge Pi PC" > strings/0x409/product # Create a new configuration (groups multiple USB functions together): mkdir configs/c.1/ mkdir configs/c.1/strings/0x409 echo "Oranbge Pi Storage" > configs/c.1/strings/0x409/configuration # Create a mass storage function and link it to the configuration: # # backing file or block device for the mass storage must not be mounted # or used by anything else, while the configuration is active umount /dev/mmcblk0 mkdir functions/mass_storage.1/ echo /dev/mmcblk0 > functions/mass_storage.1/lun.0/file ln -s functions/mass_storage.1/ configs/c.1/ # Create a rndis (something like ethernet link) function: mkdir functions/rndis.1/ ln -s functions/rndis.1/ configs/c.1/ # Activate the gadget by selecting the UDC device that should be # used for emulation: echo musb-hdrc.1.auto > UDC
To use the network link, you need to setup network interfaces on both end, either manually or via DHCP.