USB CDC-Ether (littlecore Linux)¶

Investigation results and instructions for enabling USB CDC Ethernet (ECM/RNDIS) on K230 littlecore (Linux) to establish a network connection over a USB cable.

Not available with the default kernel

All CDC Ethernet features are disabled in the default kernel configuration. A kernel rebuild is required.

Hardware Status¶

The K230 has a DWC2 OTG controller that supports USB device mode.

Item	Value
UDC controller	`91500000.usb-otg`
DWC2 driver	Loaded (91500000, 91540000)
usbotg0	OTG mode (device mode capable)
usbotg1	Host only (`dr_mode = "host"`)

In the device tree (k230_canmv.dts), usbotg0 is enabled in OTG mode, making it usable as a USB gadget.

Current Kernel Configuration¶

The USB gadget framework is enabled, but all CDC Ethernet features are disabled.

Enabled features:

CONFIG_USB_DWC2=y
CONFIG_USB_DWC2_DUAL_ROLE=y
CONFIG_USB_GADGET=y
CONFIG_USB_CONFIGFS=y
CONFIG_USB_CONFIGFS_MASS_STORAGE=y
CONFIG_USB_CONFIGFS_F_LB_SS=y
CONFIG_USB_CONFIGFS_F_HID=y
CONFIG_USB_CONFIGFS_F_UVC=y

Disabled features (CDC Ethernet):

# CONFIG_USB_CONFIGFS_NCM is not set
# CONFIG_USB_CONFIGFS_ECM is not set
# CONFIG_USB_CONFIGFS_ECM_SUBSET is not set
# CONFIG_USB_CONFIGFS_RNDIS is not set
# CONFIG_USB_CONFIGFS_EEM is not set
# CONFIG_USB_ETH is not set

How to Enable¶

1. Modify defconfig¶

Target file: k230_sdk/src/little/linux/arch/riscv/configs/k230_canmv_defconfig

Add ECM (natively supported on Linux/macOS):

CONFIG_USB_CONFIGFS_ECM=y

If Windows support is also needed, add RNDIS:

CONFIG_USB_CONFIGFS_RNDIS=y

Append these lines after the existing USB configfs settings (after CONFIG_USB_CONFIGFS_F_UVC=y).

2. Rebuild the Kernel¶

Inside the SDK Docker environment:

make linux       # Rebuild Linux kernel
make build-image # Regenerate SD card image

Building the SDK

For K230 SDK build instructions, see SDK Build.

3. configfs Setup on the Device¶

After rebuilding the kernel, mount configfs and create the ECM gadget on the device.

#!/bin/sh
# gadget-ecm.sh — USB CDC ECM gadget setup

mount -t configfs none /sys/kernel/config

mkdir -p /sys/kernel/config/usb_gadget/g1
cd /sys/kernel/config/usb_gadget/g1

echo 0x1d6b > idVendor    # Linux Foundation
echo 0x0104 > idProduct    # Multifunction Composite Gadget

mkdir -p strings/0x409
echo "Canaan Inc." > strings/0x409/manufacturer
echo "CDC Ether" > strings/0x409/product
echo "20230618" > strings/0x409/serialnumber

mkdir -p configs/c.1/strings/0x409
echo "ECM" > configs/c.1/strings/0x409/configuration

mkdir -p functions/ecm.usb0
ln -s functions/ecm.usb0 configs/c.1/

echo 91500000.usb-otg > UDC

ifconfig usb0 192.168.7.2 netmask 255.255.255.0 up

4. Host-side Setup¶

After connecting the K230 to the host PC via USB cable, configure the IP address on the host.

# Linux host
sudo ifconfig usb0 192.168.7.1 netmask 255.255.255.0 up

# Test connectivity
ping 192.168.7.2

ECM vs RNDIS¶

Protocol	Linux	macOS	Windows	Notes
ECM	No driver needed	No driver needed	Not supported	Recommended
RNDIS	No driver needed	Not supported	No driver needed	For Windows

ECM alone is sufficient for Linux/macOS. Enable RNDIS as well if Windows support is needed.

References¶

Existing gadget script examples:
- k230_sdk/src/little/buildroot-ext/package/usb_test/src/gadget-storage.sh
- k230_sdk/src/little/buildroot-ext/package/usb_test/src/gadget-hid.sh