LICHEE JACK USB DEBUGGER

Lichee-Jack USB Debugger

This sub-directory contains the USB 2.0 hub + UART converter board designed specifically for the Lichee-Jack project. It is intended to simplify development, debugging, and flashing by combining USB OTG, UART console, and power control into a single compact board.

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Overview

The LicheeRV Nano features a USB 2.0 Type-C OTG port implemented directly by the SoC PHY. This design is slightly different from a typical USB 2.0 Type-C implementation:

• SUB1 / SUB2 pins are internally multiplexed as SoC UART0

  • Used for early boot logs, kernel printk, and Linux login console

• D+ / D- pins are used as a standard USB OTG interface

  • Used for USB gadget mode (RNDIS, ECM, HID, Mass Storage, etc.)

Because UART and USB share the same physical Type-C connector, direct connection to a PC is inconvenient during development.

[!IMPORTANT] This board is not a generic USB-C hub.

It is designed specifically around the LicheeRV Nano Type-C PHY behavior, where USB OTG and UART share the same connector. Using it with unrelated USB-C devices may lead to undefined behavior.

To solve this, the Lichee-Jack USB Debugger acts as a 2-port Type-C converter:

• Port 1 (Upstream) → Connects to the host PC
• Port 2 (Downstream) → Connects to the Lichee-Jack device

The board cleanly separates:

• USB OTG data path
• UART debug console
• Power and connection detection

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Architecture & Design

USB Hub

The board uses a Microchip USB2422/MJ USB 2.0 hub controller:

• 1 upstream port (PC)

• 2 downstream ports

  • One for Lichee-Jack USB OTG
  • One internally connected to the USB-UART bridge

This allows the Lichee-Jack USB gadget functions to work normally while UART is simultaneously available on the same PC connection.

[!NOTE] The hub architecture allows USB gadget functions and UART console to operate simultaneously over a single PC connection. No cable swapping or re-plugging is required during development.

USB-UART Bridge

UART is provided by CP2102-GMR:

• Connected to Lichee-Jack UART0 (SUB1 / SUB2)

• Exposes a standard USB CDC-ACM serial device on the host

• Suitable for:

  • U-Boot console
  • Linux kernel logs
  • Root login shell

Type-C CC & Power Control

The debugger board implements CC-based power detection and control:

• PMOS power switch controlled by CC logic

• Behavior:

  • If Lichee-Jack is not connected, PMOS remains OFF

  • When Lichee-Jack is connected:

    • CC pins are pulled down by the device
    • PMOS gate is driven
    • Power path is enabled automatically

This prevents:

• Back-powering
• Floating VBUS issues
• Accidental short or unstable power states

[!NOTE] Power delivery on this board is fully hardware-controlled via CC detection. No firmware or software control is involved.

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Features

• USB 2.0 Hub (1-up / 2-down)
• Integrated USB-UART console
• Native support for LicheeRV Nano Type-C pin multiplexing
• Automatic CC-based power switching
• Works seamlessly with USB gadget modes
• No firmware required (fully hardware-driven)

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Assembly

• PCB: 2-layer board, thickness 1.6 mm

• Assembly side: Top side only

• Solder paste:

  • Sn63 / Pb37 or
  • SAC305

[!CAUTION] The USB hub uses a QFN package and requires a proper reflow profile.

Insufficient temperature or uneven heating may cause:

• Hidden cold joints
• Unreliable USB enumeration

A controlled high-temperature reflow process is strongly recommended.

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PCBA

• All components placed on top layer only
• Suitable for low-cost SMT assembly

The following files are provided in the EXT-Board latest release:

• BOM (Bill of Materials)
• CPL / Pick-and-Place
• Gerber files

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Notes

[!WARNING] Type-C cable selection is critical.

Many USB 3.x Type-C cables are SuperSpeed-only and do not carry USB-2 / SBU signals. If such a cable is used, SUB1 / SUB2 (UART0) may be physically disconnected, resulting in no UART console output even when the hardware is correct.

Always use a Thunderbolt / USB4 Type-C cable, which is required by specification to include full USB-2 wiring.

[!TIP] No UART console? Try flipping the Type-C connector on the Lichee-Jack side.

Unlike USB D+ / D-, SUB1 / SUB2 (UART0) are not orientation-symmetric. Depending on plug orientation, the UART pins may not be connected.

Simply unplug and reverse the Type-C connector to restore UART functionality.

• Designed specifically for Lichee-Jack / LicheeRV Nano Type-C behavior
• Not intended as a generic USB-C hub
• Recommended for development, debugging, and factory flashing workflows