Scufpad

A Linux application that bridges a Scuf Envision Pro V2 controller to a virtual Xbox Elite 2 controller via the uinput subsystem.

Overview

The Scuf Envision Pro V2 controller (VID: 0x1b1c, PID: 0x3a05) uses highly non-standard evdev mappings that cause incorrect button/axis assignments in most Linux games. This bridge:

1. Reads input from the physical Scuf controller via evdev
2. Translates the non-standard mappings to standard Xbox Elite 2 format
3. Outputs to a virtual gamepad that games recognize correctly

The virtual controller appears to games as a standard Xbox Elite 2 controller (Microsoft VID: 0x045e, PID: 0x0b12).

Requirements

• Linux with uinput support
• .NET 10.0 or later
• Scuf Envision Pro V2 controller (VID: 0x1b1c, PID: 0x3a05)

Quick Start

# 1. Set up udev rules (one-time)
sudo tee /etc/udev/rules.d/99-scuf.rules << 'EOF'
SUBSYSTEM=="input", ATTRS{idVendor}=="1b1c", ATTRS{idProduct}=="3a05", MODE="0666"
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="1b1c", ATTRS{idProduct}=="3a05", MODE="0666"
KERNEL=="uinput", MODE="0666"
EOF

# 2. Reload udev rules
sudo udevadm control --reload-rules && sudo udevadm trigger

# 3. Load uinput module
sudo modprobe uinput

# 4. Run the bridge
dotnet run --project src/Scufpad

Game-Specific Configuration

Steam Games (Important!)

For the best experience with Steam games, you need to disable Steam Input and tell SDL to ignore the physical controller:

1. Disable Steam Input for the Game

1. Right-click the game in Steam → Properties
2. Go to Controller tab
3. Set Override for [Game] to Disable Steam Input

2. Add Launch Options (SDL Games)

For games using SDL (like Stardew Valley), add this to the Steam launch options:

SDL_GAMECONTROLLER_IGNORE_DEVICES=0x1b1c/0x3a05 %command%

This tells SDL to ignore the physical Scuf controller so only the virtual Xbox controller is used.

Example for Stardew Valley:

1. Right-click Stardew Valley → Properties
2. In Launch Options, enter:

   SDL_GAMECONTROLLER_IGNORE_DEVICES=0x1b1c/0x3a05 %command%
   

3. In the Controller tab, disable Steam Input

Non-Steam Games

The bridge grabs the physical controller exclusively, so most games will only see the virtual Xbox controller. However, some games may need the SDL_GAMECONTROLLER_IGNORE_DEVICES environment variable set before launching.

Setup Details

1. Create udev rules

Create /etc/udev/rules.d/99-scuf.rules:

sudo tee /etc/udev/rules.d/99-scuf.rules << 'EOF'
SUBSYSTEM=="input", ATTRS{idVendor}=="1b1c", ATTRS{idProduct}=="3a05", MODE="0666"
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="1b1c", ATTRS{idProduct}=="3a05", MODE="0666"
KERNEL=="uinput", MODE="0666"
EOF

2. Reload udev rules

sudo udevadm control --reload-rules
sudo udevadm trigger

Then unplug and replug your controller.

3. Load the uinput module

sudo modprobe uinput

To load uinput automatically on boot:

echo 'uinput' | sudo tee /etc/modules-load.d/uinput.conf

4. Verify setup

# Check controller is detected
lsusb | grep 1b1c:3a05

# Check device permissions
ls -la /dev/input/by-id/*Envision*
ls -la /dev/uinput

Usage

# Run from source
dotnet run --project src/Scufpad

# Or build and run
dotnet build
./src/Scufpad/bin/Debug/net10.0/Scufpad

# AOT publish (single binary)
dotnet publish -c Release -r linux-x64

Architecture

Data Flow Pipeline

Physical Scuf Controller
        ↓
EvdevReader (reads evdev events)
        ↓
InputPoller (multiplexes with poll(2), 4ms timeout ≈ 250Hz)
        ↓
EnvisionMapping (translates Scuf's non-standard mappings)
        ↓
InputFilter (applies deadzone and jitter filtering)
        ↓
VirtualGamepad (emits to virtual Xbox Elite 2 via uinput)
        ↓
Games see standard Xbox controller

Project Structure

src/Scufpad/
├── Discovery/           # Device discovery via /sys/class
│   └── DeviceDiscovery.cs
├── Input/               # Input device readers
│   ├── EvdevReader.cs   # Reads evdev input events
│   ├── HidrawReader.cs  # Reads raw HID reports (optional)
│   └── InputPoller.cs   # Multiplexes input with poll(2)
├── Interop/             # P/Invoke bindings
│   ├── Hidraw.cs        # hidraw ioctl constants
│   ├── Libc.cs          # libc functions (open, read, ioctl, poll)
│   ├── LinuxInput.cs    # input_event struct, button/axis codes
│   └── Uinput.cs        # uinput ioctl constants
├── Mapping/             # Input translation and filtering
│   ├── EnvisionMapping.cs  # Scuf V2 → Xbox mapping
│   ├── InputFilter.cs      # Deadzone and jitter filtering
│   └── InputState.cs       # Controller state representation
├── Output/              # Virtual device creation
│   └── VirtualGamepad.cs   # Creates Xbox Elite 2 via uinput
├── Services/            # Main service orchestration
│   └── BridgeService.cs    # Main loop coordination
└── Program.cs           # Entry point

Hardware Mapping Reference

Scuf Envision Pro V2 Axis Mappings

The V2 uses completely non-standard axis positions:

Scuf Axis	evdev Code	Value Range	Maps To
Left Stick X	ABS_X (0)	-32768 to 32767	Left Stick X
Left Stick Y	ABS_Y (1)	-32768 to 32767	Left Stick Y
Right Stick X	ABS_Z (2)	-32768 to 32767	Right Stick X
Left Trigger	ABS_RX (3)	0 to 1023	Left Trigger
Right Trigger	ABS_RY (4)	0 to 1023	Right Trigger
Right Stick Y	ABS_RZ (5)	-32768 to 32767	Right Stick Y
D-pad X	ABS_HAT0X (16)	-1 to 1	D-pad X
D-pad Y	ABS_HAT0Y (17)	-1 to 1	D-pad Y

Bold = Non-standard mapping (differs from typical Xbox controllers)

Scuf Envision Pro V2 Button Mappings

The V2 uses highly non-standard button codes:

Scuf Button	evdev Code	Standard Code	Maps To
A	BTN_SOUTH (0x130)	BTN_SOUTH	A Button
B	BTN_EAST (0x131)	BTN_EAST	B Button
X	BTN_C (0x132)	BTN_WEST	X Button
Y	BTN_NORTH (0x133)	BTN_NORTH	Y Button
LB	BTN_WEST (0x134)	BTN_TL	Left Bumper
RB	BTN_Z (0x135)	BTN_TR	Right Bumper
L3	BTN_TL2 (0x138)	BTN_THUMBL	Left Stick Click
R3	BTN_TR2 (0x139)	BTN_THUMBR	Right Stick Click
Select	BTN_TL (0x136)	BTN_SELECT	Back/Select
Start	BTN_TR (0x137)	BTN_START	Start
Guide	BTN_MODE (0x13c)	BTN_MODE	Guide/Home
Paddle 1	BTN_TRIGGER_HAPPY1	-	Paddle 1
Paddle 2	BTN_TRIGGER_HAPPY2	-	Paddle 2
Paddle 3	BTN_TRIGGER_HAPPY3	-	Paddle 3

Bold = Non-standard mapping

Note: The V2 only has 3 paddle buttons, not 4.

Performance Tuning

The bridge is optimized for low-latency input:

Setting	Value	Purpose
Poll timeout	4ms	~250Hz polling for sub-frame latency at 60fps
Stick deadzone	3500 (~10.7%)	Eliminates stick drift
Trigger deadzone	10 (~1%)	Minimal deadzone for responsiveness
Stick jitter threshold	300	Filters analog noise
Trigger jitter threshold	20 (~2%)	Low threshold for responsive triggers

These defaults can be adjusted in InputFilter.cs if needed.

Troubleshooting

"Permission denied" errors

# Verify udev rules
cat /etc/udev/rules.d/99-scuf.rules

# Reload rules
sudo udevadm control --reload-rules && sudo udevadm trigger

# Unplug and replug controller
# Check permissions
ls -la /dev/hidraw* /dev/uinput /dev/input/event*

"uinput device not found"

# Load the module
sudo modprobe uinput

# Verify it's loaded
lsmod | grep uinput

Controller not detected

# Check USB connection
lsusb | grep 1b1c

# View kernel messages
dmesg | tail -20

# Ensure you have the V2 controller (PID 3a05)

Game sees both controllers / double input

Make sure:

1. The bridge is running before starting the game
2. Steam Input is disabled for the game
3. SDL_GAMECONTROLLER_IGNORE_DEVICES=0x1b1c/0x3a05 is set (for SDL games)

Trigger feels laggy or unresponsive

This was fixed in recent updates. If you experience trigger latency:

1. Ensure you're running the latest version
2. The poll timeout should be 4ms (not 100ms)
3. The trigger jitter threshold should be 20 (not 75)

Building

# Debug build
dotnet build

# Release build
dotnet build -c Release

# Run tests
dotnet test

# AOT publish (single binary, no .NET runtime required)
dotnet publish -c Release -r linux-x64

Testing

# Run all tests
dotnet test

# Run specific test project
dotnet test tests/scufpad.Tests.Unit
dotnet test tests/scufpad.Tests.Integration

# Test with evtest
evtest  # Select the virtual Xbox controller to verify output

Technical Notes

Why evdev grab is necessary

The bridge grabs the physical controller exclusively using EVIOCGRAB to:

1. Prevent games from seeing the raw Scuf input with wrong mappings
2. Prevent double-input (one from physical, one from virtual)

Why hidraw is optional on V2

V1 hardware reportedly didn't expose the right trigger via evdev, requiring hidraw fallback. V2 hardware provides both triggers via evdev (ABS_RX for LT, ABS_RY for RT), so hidraw is no longer needed. Hidraw processing is disabled to avoid latency issues from stale data.

Multiple evdev devices

The Scuf controller exposes multiple input devices (joystick, mouse emulation, etc.). All are grabbed exclusively to prevent input leakage.

License

MIT