USB OTG

Lichee-Jack uses the LicheeRV-Nano SoC (sg2002) USB 2.0 OTG controller and primarily operates in USB gadget (device) mode. This allows Lichee-Jack to present itself to a host computer as different USB devices such as Ethernet, Serial, HID, or Mass Storage.

Features

USB 2.0 OTG (Device / Gadget mode)
Compatible with Linux USB Gadget framework
Supports composite gadgets (multiple functions at once)
Designed for payload-style workflows (plug & run)

OTG Role Initialization

During early system initialization, the OTG role must be forced to device mode.

Add the following command to your init sequence:


echo "device" > /proc/cviusb/otg_role

This ensures the USB controller always enumerates as a USB device when connected to a host.

Gadget Management

Lichee-Jack uses linux-usb-gadgets/gt as a lightweight gadget loader and manager.

gt is a simple userspace tool that:

Uses ConfigFS to configure USB gadgets
Loads gadgets from a modern, declarative configuration file
Supports multiple gadget functions in one device

Repository:

GitHub: linux-usb-gadgets/gt

Supported Gadget Functions

Depending on the configuration, Lichee-Jack can expose:

CDC ACM – USB serial console
CDC ECM / NCM – USB Ethernet
HID – Keyboard / Mouse payloads
Mass Storage – Disk image emulation

These can be combined into a single composite USB device.

Example Workflow

System boots in Mode 0 (Debug)
OTG role is forced to device
gt loads the gadget configuration
Host PC detects Lichee-Jack as a USB device
Payload services start automatically

Notes

Host-side drivers are usually not required (CDC / HID are class-compliant)
USB gadget behavior can be switched dynamically via Mode Switch payloads