Joypad Core

Universal controller firmware foundation for adapters, controllers, and input systems.

Joypad Core is a modular, high-performance firmware platform for building controller adapters, custom controllers, and input/output bridges across USB, Bluetooth, and native game console protocols.

Formerly known as USBRetro, this project now serves as the foundational firmware layer of the Joypad ecosystem — a universal platform for extending how controllers work, connect, and evolve.

Joypad Core focuses on real-time controller I/O, protocol translation, and flexible routing, making it easy to build everything from classic console adapters to next-generation, assistive, and AI-augmented input devices.

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What Joypad Core Enables

• Universal input/output translation — Convert USB HID devices into native console protocols and vice versa.
• Modular firmware apps — Build specific bridges like usb2usb, usb2gc, snes2usb, passthrough adapters, merged inputs, and hybrid devices — all on a shared core.
• Flexible routing & passthrough — Support multi-output controllers, input merging, chaining devices, and advanced mods.
• Hardware-agnostic foundation — Designed to run across RP2040 today, with future portability to ESP32 and nRF platforms.
• Foundation for accessibility & assistive play — Enables custom controllers and input extensions for gamers with diverse needs.

Joypad Core is the real-time nervous system of the Joypad platform.

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Supported Outputs

Output	Features	Documentation
USB Device	HID Gamepad, XInput, Xbox OG, Xbox One, PS3, PS4, PS Classic, Switch	Docs
PCEngine / TurboGrafx-16	Multitap (5 players), Mouse, 2/3/6-button	Docs
GameCube / Wii	Profiles, Rumble, Keyboard mode	Docs
Nuon DVD Players	Controller, Spinner (Tempest 3000), IGR	Docs
3DO Interactive Multiplayer	8 players, Mouse, Extension passthrough	Docs
Casio Loopy	4 players (experimental)	Docs

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Products

Pre-built adapters available at controlleradapter.com:

• USB-2-PCE - PCEngine/TurboGrafx-16 adapter
• GC USB - GameCube/Wii adapter with profiles
• NUON USB - Nuon DVD player adapter

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Supported USB Devices

Controllers:

• Xbox (OG/360/One/Series X|S)
• PlayStation (Classic/DS3/DS4/DualSense)
• Nintendo Switch (Pro/Joy-Cons)
• 8BitDo (PCE 2.4g, M30, Adapters)
• Generic HID gamepads

Peripherals:

• USB Keyboards (full HID support)
• USB Mice (PCEngine mouse, Nuon spinner, 3DO mouse)
• USB Hubs (up to 8 devices for 3DO)

Complete hardware compatibility list

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For Users: Updating Firmware

Quick Flash

1. Download latest .uf2 from Releases
2. Enter bootloader:
   • USB-2-PCE / NUON / 3DO: Hold BOOT + connect USB-C
   • GC USB: Just connect USB-C (no button)
3. Drag .uf2 file to RPI-RP2 drive
4. Done! Drive auto-ejects when complete

Full installation guide

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For Developers: Building Firmware

Quick Start

# Install ARM toolchain (macOS)
brew install --cask gcc-arm-embedded cmake git

# Clone and initialize
git clone https://github.com/joypad-ai/joypad-core.git
cd joypad-core && make init

# Build specific product
make usb2gc         # GameCube adapter
make usb2pce        # PCEngine adapter
make usb2nuon       # Nuon adapter
make usb23do        # 3DO adapter

Build Commands

make init          # Initialize submodules (one-time setup)
make all           # Build all products
make clean         # Clean build artifacts

# Build specific products
make usb2pce       # USB2PCE (KB2040 + PCEngine)
make usb2gc        # USB2GC (KB2040 + GameCube)
make usb2nuon      # USB2Nuon (KB2040 + Nuon)
make usb23do       # USB23DO (KB2040 + 3DO)
make usb2loopy     # USB2Loopy (KB2040 + Casio Loopy)
make snes23do      # SNES23DO (SNES→3DO bridge)

Output firmware files appear in releases/ directory.

Complete build guide

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Documentation

• Installation Guide - Flashing firmware, troubleshooting
• Hardware Compatibility - Supported controllers, boards, DIY builds
• Build Guide - Developer setup, architecture

Console-Specific Guides

• GameCube/Wii - Profiles, keyboard mode, rumble
• PCEngine/TurboGrafx-16 - Multitap, mouse, button modes
• Nuon - Controller, Tempest 3000 spinner, IGR
• 3DO - 8-player support, mouse, profiles
• Casio Loopy - Experimental support

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Architecture

Joypad Core uses a modular architecture:

• RP2040 - Dual-core ARM Cortex-M0+ microcontroller
• TinyUSB - USB host stack for polling USB devices
• PIO - Programmable I/O for timing-critical console protocols
• Dual-Core: Core 0 handles USB input, Core 1 runs console output
• Router - Flexible input→output routing (SIMPLE/MERGE/BROADCAST)
• Apps - Per-product configuration (router, profiles, features)

See CLAUDE.md for detailed architecture

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Community & Support

• Discord: discord.joypad.com - Community chat
• Issues: GitHub Issues - Bug reports
• Email: support@controlleradapter.com - Product support

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Acknowledgements

• Ha Thach - TinyUSB
• David Shadoff - PCEMouse foundation
• FCare - USBTo3DO 3DO protocol implementation
• Ryzee119 - tusb_xinput
• SelvinPL - lufa-hid-parser
• JonnyHaystack - joybus-pio

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License

Joypad Core is licensed under the Apache-2.0 License.

The Joypad name and branding are trademarks of Joypad Inc.