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7.2.8 USB Gadget User Guide

This chapter describes how to use the USB Gadget feature on the development board, including configuring the USB 2.0 Type-C interface for ADB mode and RNDIS mode.

Hardware Limitations​

USB Interface Overview​

The RDK S100 development board provides the following USB interfaces:

Interface TypeLocationQuantityOperating ModePurpose
USB Type-CJ161Device OnlyImage flashing, debug serial port, USB Gadget
USB 3.0 Type-AJ19/J204Host OnlyConnect USB peripherals (USB drives, keyboard, mouse, etc.)
Important Limitations
  1. USB Type-C (J16) supports Device mode only. It does not support Host mode and cannot be used to read USB drives or connect other USB devices.
  2. USB 3.0 Type-A (J19/J20) supports Host mode only and cannot be configured as Gadget mode.
  3. The USB Type-C interface includes a debug serial port function. The CH340 chip converts debug serial ports from the Main domain and MCU domain into a USB interface.
  4. Note the USB 2.0 camera connection limitations. For details, see the USB Camera documentation in the Basic Application chapter.

The RDK S600 development board provides the following USB interfaces:

Interface TypeLocationQuantityOperating ModePurpose
USB Type-CJ41Device OnlyImage flashing, debug serial port, USB Gadget
USB 3.2 Gen 1x1 Type-AJ7/J8/J96Host OnlyConnect USB peripherals (USB drives, keyboard, mouse, etc.)
Important Limitations
  1. USB Type-C (J4) supports Device mode only. It does not support Host mode and cannot be used to read USB drives or connect other USB devices.
  2. USB 3.2 Type-A (J7/J8/J9) supports Host mode only and cannot be configured as Gadget mode.
  3. The USB Type-C interface includes a debug serial port function. The CH340 chip converts debug serial ports from the Main domain and MCU domain into a USB interface.
  4. Note the USB 2.0 camera connection limitations. For details, see the USB Camera documentation in the Basic Application chapter.

USB Gadget Feature Overview​

USB Gadget is a framework provided by the Linux kernel that allows a device to connect to a host as a USB peripheral (Device). Through the USB Gadget framework, RDK development boards can emulate various USB device functions.

RDK development boards support the following Gadget functions through the usb-gadget.sh script:

FunctionDescription
adbAndroid Debug Bridge, used for ADB debugging
rndisRemote NDIS, virtual network adapter function that enables USB network sharing

Usage​

Switch to ADB Mode​

ADB (Android Debug Bridge) mode allows users to debug and transfer files through the USB Type-C interface.

Start ADB mode:

usb-gadget.sh start adb

Example output:

Detecting platform:
 board : D-Robotics RDK S100 V0P5
 udc   : 39820000.dwc3
Creating the USB gadget
Loading composite module
Mount ConfigFS and create Gadget
Creating gadget directory g_comp
OK
init configfs...
Setting Vendor and Product ID's
OK
...
Creating ACM gadget functionality
OK
Binding USB Device Controller
OK
usb-gadget start succeed.

Stop ADB mode:

usb-gadget.sh stop adb

Switch to RNDIS Mode​

RNDIS (Remote Network Driver Interface Specification) mode virtualizes the USB Type-C interface as a network adapter, enabling USB network sharing. After connecting to a PC, a remote network adapter device appears on the computer.

Start RNDIS mode:

usb-gadget.sh stop adb
usb-gadget.sh start rndis

Example output:

Stopping the USB gadget
Stoping & Delete usb-gadget g_comp
waiting...
...
OK
Bind functions...
Bind functions according to .usb-config file
bind gadget rndis...
Creating RNDIS gadget functionality
OK
Pre run userspace daemons(eg. adb)...
0
waiting
.
OK
Binding USB Device Controller
OK
Run some userspace daemons(eg. usb_camera)...
usb-gadget start succeed.

After connecting to a PC, you can see the Remote NDIS Compatible Device network adapter on the computer's network configuration page:

RNDIS_Device

Configure network IP:

Configure the USB network adapter IP address on the development board:

ifconfig usb0 192.168.1.110

Configure the remote network adapter IP address on the PC (must be on the same subnet as the development board):

NETWORK_CONFIG

Verify network connectivity:

Ping the PC IP from the development board:

ping 192.168.1.111

Stop RNDIS mode:

usb-gadget.sh stop rndis

FAQ​

Windows Cannot Recognize RNDIS Device​

If the RNDIS device is not recognized correctly after connecting on Windows, possible causes include:

  1. OS descriptors not loaded on first connection: Windows records device information in the registry. If the correct OS descriptors were not present on the first connection, subsequent connections will not request them again.

    Solution: Delete the device record in the registry:

    HKLM\SYSTEM\CurrentControlSet\Control\usbflags\[USB_VID+USB_PID+bcdRelease]\osvc

  2. Manual driver installation: In Device Manager, find the unrecognized device, right-click and select "Update driver", choose "Browse my computer for drivers", then select "Let me pick from a list of available drivers on my computer", and choose "Network adapters" -> "Microsoft" -> "Remote NDIS Compatible Device".

ADB Device Not Recognized​

If the ADB device is not recognized on the PC:

  1. Confirm that the ADB driver is installed (Windows) or the adb tool is installed (Linux/macOS)
  2. Check whether the USB cable supports data transfer
  3. Use the adb devices command to check whether the device is recognized

Device Not Recognized After Switching Modes​

If the PC does not recognize the new device after switching Gadget modes:

  1. Disconnect and reconnect the USB cable
  2. Run usb-gadget.sh stop to stop the current mode, then start the new mode
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