usb-hid-relay

tldr;

Fuck League of Legends, fuck Riot and fuck Vanguard.

Relay mouse events from Linux to Windows, over UDP via Pi acting as a HID device.

Motivations

I use Linux for everything in my life other than League of Legends, so I have an old PC setup as a server for League of Legends. For this I use Sunshine on the Windows PC to host and Moonlight on the Linux machine to remote in. Since everything is wired locally, this works with virtually 0 noticeable latency. The problem is the shitty abomination that Vanguard is blocks the virtual mouse that Sunshine + Moonlight uses.

This project is an attempt to fix this.

Demo

Setup/Environment

• Windows 11 PC
  • Sunshine
  • HDMI dummy plug
  • Auto login - nice if/when we have to reboot
• Framework Laptop
  • Arch
  • Hyprland !IMPORTANT! - USB Host uses hyprctl for getting active windows.
  • Moonlight
• Raspberry Pi Zero 2 w
  • ENC28J60 & Dupont wires optionally for lower latency
  • MicroUSB to USB

Building

Build USB Host native:

gcc -o usb_host usb_host.c window_monitor.c # for linux machine

Install ARM cross-compiler:

sudo apt-get install gcc-aarch64-linux-gnu  # for Pi (64-bit OS)

Cross-compile for ARM:

aarch64-linux-gnu-gcc -o usb_client usb_client.c  # for Pi (64-bit)

Raspberry Pi setup

Need to setup the Pi up to act as a USB host, so Windows recognizes it as a mouse.

---

Enable modules and drivers:

echo "dtoverlay=dwc2" | sudo tee -a /boot/config.txt
sudo echo "dwc2" | sudo tee -a /etc/modules
sudo echo "libcomposite" | sudo tee -a /etc/modules

Double check:

sudo nano /boot/firmware/config.txt

and add dtoverlay if it's not under [all]

[all]
dtoverlay=dwc2

Reboot

sudo reboot
lsmod | grep dwc2 # Should now show dwc2

---

Create config scripts:

sudo touch /usr/bin/pi_usb
sudo chmod +x /usr/bin/pi_usb

sudo nano /usr/bin/pi_usb

and enter, which creates the USB gadget when ran:

#!/bin/bash

GADGET_DIR="/sys/kernel/config/usb_gadget/usb_pi"

# Cleanup function
cleanup_gadget() {
    if [ -d "$GADGET_DIR" ]; then
        echo "Cleaning up existing gadget..."
        cd "$GADGET_DIR"
        
        # Unbind from UDC (important to do first!)
        if [ -f UDC ]; then
            echo "" > UDC 2>/dev/null || true
        fi
        
        # Remove symlinks from configs
        find configs/*/hid.usb* -type l -delete 2>/dev/null || true
        
        # Remove functions
        find functions/hid.usb* -type d -exec rmdir {} \; 2>/dev/null || true
        
        # Remove config strings
        find configs/*/strings/* -type d -exec rmdir {} \; 2>/dev/null || true
        
        # Remove configs
        find configs/* -type d -exec rmdir {} \; 2>/dev/null || true
        
        # Remove gadget strings
        find strings/* -type d -exec rmdir {} \; 2>/dev/null || true
        
        # Remove the gadget itself
        cd /sys/kernel/config/usb_gadget/
        rmdir usb_pi 2>/dev/null || true
        
        echo "Cleanup complete"
        sleep 1
    fi
}

# Load required modules
modprobe libcomposite

# Clean up first
cleanup_gadget

# Create fresh gadget
cd /sys/kernel/config/usb_gadget/
mkdir -p usb_pi
cd usb_pi

echo 0x1d6b > idVendor
echo 0x0104 > idProduct
echo 0x0100 > bcdDevice
echo 0x0200 > bcdUSB

mkdir -p strings/0x409
echo "fedcba9876543210" > strings/0x409/serialnumber
echo "Noah Giles" > strings/0x409/manufacturer
echo "USB Mouse" > strings/0x409/product

mkdir -p configs/c.1/strings/0x409
echo "Config 1: HID Mouse" > configs/c.1/strings/0x409/configuration
echo 250 > configs/c.1/MaxPower

# Add HID mouse function
mkdir -p functions/hid.usb0
echo 2 > functions/hid.usb0/protocol
echo 1 > functions/hid.usb0/subclass
echo 4 > functions/hid.usb0/report_length
echo -ne \\x05\\x01\\x09\\x02\\xa1\\x01\\x09\\x01\\xa1\\x00\\x05\\x09\\x19\\x01\\x29\\x05\\x15\\x00\\x25\\x01\\x95\\x05\\x75\\x01\\x81\\x02\\x95\\x01\\x75\\x03\\x81\\x03\\x05\\x01\\x09\\x30\\x09\\x31\\x15\\x81\\x25\\x7f\\x75\\x08\\x95\\x02\\x81\\x06\\x09\\x38\\x15\\x81\\x25\\x7f\\x75\\x08\\x95\\x01\\x81\\x06\\xc0\\xc0 > functions/hid.usb0/report_desc

ln -s functions/hid.usb0 configs/c.1/

# Bind to UDC
UDC_DEVICE=$(ls /sys/class/udc | head -n1)
echo "$UDC_DEVICE" > UDC

echo "USB HID Mouse gadget configured successfully!"
echo "Device: $UDC_DEVICE"
echo "HID device should be at /dev/hidg0"

---

Create Systemd service, to auto-start if the Pi reboots.

sudo nano /etc/systemd/system/pi_usb.service

with the following contents:

[Unit]
Description=Run my custom script at startup
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/bin/pi_usb
RemainAfterExit=yes
User=root

[Install]
WantedBy=multi-user.target

and to start the service:

sudo systemctl daemon-reload
sudo systemctl enable pi_usb.service
sudo systemctl start pi_usb.service

---

Check it worked:

# Should show a UDC device
ls /sys/class/udc/
# Should exist now
ls -l /dev/hidg0

If they don't show, gg figure it out.

Running

You should have:

• usb_host - Intended for Linux (sending mouse events to Pi)
• usb_client - Intended for Raspberry Pi (receiving mouse events from Linux and forward to Windows)

---

Pi

Copy usb_client to Pi:

scp usb_client noah@usbpi.local:/home/noah/

and run using:

sudo ./usb_client

We should see two log lines for opening the HID device and listening to port 5555.

---

Linux

Find mouse:

cat /proc/bus/input/devices

You are looking for the event number of your mouse.

Then run:

sudo -E ./usb_host -d /dev/input/event5 -i 192.168.0.102 -w stream.Moonlight -s 1.677

sudo -E or sudo HYPRLAND_INSTANCE_SIGNATURE=$HYPRLAND_INSTANCE_SIGNATURE so we can use hyprctl.
event5 = mouse event number
192.168.0.102 = IP of Pi
stream.Moonlight = Class of window (I only want to send mouse events when Moonlight is active)
1.677 = Sensitivity scaling`

Windows Alternative

Few notes
This requires a mouse plugged into the Windows host, a dummy plug works and is probably desirable.
This will flag malware warnings etc on Windows, C'est la Vie.

Build Windows User Client

sudo pacman -S mingw-w64-gcc

x86_64-w64-mingw32-gcc -o usb_client_win.exe windows/usb_client_interception.c windows/interception.dll -lws2_32

Windows Setup

• Download oblitum's interception
• Open command prompt in the command line installer directory
• Run install-interception.exe /install
• Reboot

Running

• Copy the usb_client_win.exe & interception.dll to the Windows machine.
• Run usb_client_win.exe (must be in same location as the dll)
• Run the usb_host on Linux host, same as above method for Pi.