Switch Pico Controller Bridge

Raspberry Pi Pico firmware that emulates a Switch Pro controller over USB and a host bridge that forwards real gamepad input over UART (with rumble round-trip).

What you get

• Firmware (switch-pico.cpp + switch_pro_driver.*): acts as a wired Switch Pro. Takes controller reports over UART1 and passes rumble from the Switch back over UART.
• Python bridge (switch_pico_bridge.controller_uart_bridge / CLI controller-uart-bridge): reads SDL2 controllers on the host, sends reports over UART, and applies rumble locally. Hot‑plug friendly and cross‑platform (macOS/Windows/Linux).
• Colour override (controller_color_config.h): compile‑time RGB overrides for body/buttons/grips as seen by the Switch.

Quick start

1. Flash the Pico with firmware/switch-pico.uf2 (or build your own) using BOOTSEL drag-and-drop (see “Manual UF2 flashing” below).
2. Wire Pico UART1 to a USB↔UART adapter (GPIO4 TX, GPIO5 RX, GND) and plug that adapter into your host PC.
3. Enable System Settings → Controllers and Sensors → Pro Controller Wired Communication on the Switch.
4. Install the Python bridge (see “Python bridge”) and run controller-uart-bridge --interactive.
5. Connect the Pico to the Switch (dock USB-A or USB-C OTG); the Switch should see it as a wired Pro Controller.

Planned features

• IMU support for motion controls (gyro/accelerometer passthrough for controllers that support it to the Switch) (WIP branch on gyrov3).

Limitations

• No motion controls/IMU passthrough yet (planned).
• No NFC/amiibo/IR support.
• Rumble is best-effort: it depends on the Switch sending rumble and SDL2 being able to drive haptics on your specific controller.
• Requires a host computer running the bridge; the Pico is not a Bluetooth/USB host for controllers.

Uses

• Remote couch co-op: friends connect via Parsec while the host streams the Switch via a low-latency capture device (e.g., Magewell Pro Capture) and runs the bridge (see setup below).
• Switch automation (Python): write scripts/bots that drive the Pico directly using switch_pico_bridge.switch_pico_uart (see examples/example_switch_macro.py).
• Twitch chat plays: translate chat messages into controller actions on the host, then forward them over UART to the Pico.

Remote couch co-op setup (example)

1. Connect the Switch to a low-latency capture device on the host PC; view it in OBS (or your preferred viewer).
2. Run controller-uart-bridge on the host PC and connect the Pico to the Switch for input.
3. Have friends connect to the host PC using Parsec; they use their controllers on their end, which Parsec forwards to the host (SDL2 sees them).
4. Optional audio routing: Voicemeeter Potato + a virtual audio cable can help manage capture/voice/game audio mixing:
   • Voicemeeter Potato: https://vb-audio.com/Voicemeeter/potato.htm
   • VB-CABLE: https://vb-audio.com/Cable/index.htm

End-to-end data flow (input + rumble)

INPUT (buttons/sticks)
[Any controller] -> [Host OS HID] -> [SDL2 GameController] -> [controller-uart-bridge]
                 -> [USB↔UART adapter + UART serial] -> [Pico firmware] -> [USB (Switch Pro)]
                 -> [Nintendo Switch]

RUMBLE (force feedback)
[Nintendo Switch] -> [USB rumble output report] -> [Pico firmware]
                 -> [UART serial + USB↔UART adapter] -> [controller-uart-bridge]
                 -> [SDL2 haptics] -> [Any controller motors]

Hardware wiring (Pico)

• UART1 pins (fixed in firmware):
  • TX: GPIO4 (Pico pin 6) → RX of your USB-serial adapter.
  • RX: GPIO5 (Pico pin 7) → TX of your USB-serial adapter.
  • GND: common ground between Pico and adapter.
• Baud rate: 921600 (default). Some adapters only handle 500,000; both bridges accept a --baud flag.
• Keep logic at 3.3V; do not feed 5V UART into the Pico.

Full hookup checklist

1. Gather the hardware

   • Raspberry Pi Pico flashed with the provided firmware.
   • USB-A-to-micro USB cable (or USB-C if you use a Pico W) to connect the Pico to the Switch or a PC for testing.
   • USB-to-UART adapter capable of 3.3 V logic at 921600 baud (FT232, CP2102, CH340, etc.).
   • Three dupont wires (TX, RX, GND). Optionally add heat-shrink or a small proto board if you want something more permanent.

2. Wire the Pico to the USB-to-UART adapter

   • Pico GPIO4 → adapter RX (sometimes labelled RXD, DI, or R).
   • Pico GPIO5 → adapter TX (TXD, DO, or T).
   • Pico GND → adapter GND. Tie grounds even if the adapter is already USB-powered.
   • Leave VBUS/VCC unconnected unless your adapter explicitly supports 3.3 V power output and you intend to power the Pico from it (the bridge expects the Pico to be powered from USB instead).

3. Connect everything to the host and Switch

   • Plug the USB-to-UART adapter into the computer that will run the Python bridge. Note the COM port (Device Manager > Ports) on Windows or /dev/cu.*//dev/ttyUSB* path on macOS/Linux; pass it via --map/--ports.
   • Connect the Pico's micro USB port to the Nintendo Switch (via the dock's USB-A port, a USB-C OTG adapter, or a PC if you are only testing). The Pico enumerates as a Switch Pro Controller over USB.
   • On the Switch, enable System Settings → Controllers and Sensors → Pro Controller Wired Communication.
   • Any SDL-compatible gamepads you want to use should also be plugged into (or paired with) the same host computer that runs the Python bridge; the bridge is the one reading them.

Finding your USB↔UART adapter “description” (port filtering)

If you have multiple serial/COM devices, you can filter which ports the bridge will consider using the port description (or vendor/product text) shown by the OS.

• macOS/Linux (terminal):
  • Quick list with descriptions: python -m serial.tools.list_ports -v
  • Then run the bridge with a filter, for example: controller-uart-bridge --interactive --include-port-desc CP210
• Windows:
  • Device Manager → Ports (COM & LPT) → open your adapter → copy the device name/vendor text.
  • Then run: controller-uart-bridge --interactive --include-port-desc "USB-SERIAL CH340"

Filters you can use:

• --include-port-desc SUBSTR (repeatable): only consider ports whose description contains the substring.
• --ignore-port-desc SUBSTR (repeatable): exclude ports whose description contains the substring.
• --all-ports: include non-USB serial devices in discovery (useful if your adapter isn’t tagged as USB by the OS).

4. Power-on order and sanity checks

   • Power the Switch/dock so the Pico gets 5 V over USB; its USB stack must stay alive while the bridge streams data.
   • On the host computer, run controller-uart-bridge --list-controllers to make sure SDL sees your pads, then start the bridge with --map/--ports (or --interactive) referencing the adapter path you found earlier.
   • Watch the Rich console output: you should see each controller paired with a UART port and the rumble loop logging reconnects if cables are unplugged.

5. Common pitfalls

   • A flipped TX/RX pair results in silence (no button presses); swap them if the Pico never shows input.
   • Some adapters default to 5 V logic—move the jumper to 3.3 V before touching the Pico.
   • If you use multiple adapters, label each cable; COM port numbers can change between boots.

• When testing on a PC before plugging into a Switch, you can verify activity with the lightweight switch_pico_bridge.switch_pico_uart helper or the Windows "Game Controllers" panel.

Building and flashing firmware

Prereqs: Pico SDK + CMake toolchain set up.

One-shot build + flash (picotool)

python3 build.py

• Requires picotool on your PATH (or set PICOTOOL_PATH=/path/to/picotool) and a connected Pico in BOOTSEL mode to automatically flash.
• Set ELF_PATH to override the default build/switch-pico.elf.

Manual build

cmake -S . -B build -DSWITCH_PICO_LOG=OFF
cmake --build build -j

This produces a .uf2 you can flash (typically build/switch-pico.uf2).

Manual UF2 flashing (BOOTSEL, no tools)

If you already have a built (or use the pre-built one in firmware/) .uf2, you can flash it without rebuilding:

1. Unplug the Pico.
2. Hold the BOOTSEL button.
3. While holding BOOTSEL, plug the Pico into your computer over USB (not the Switch), then release BOOTSEL.
4. A USB mass-storage drive (usually RPI-RP2) will appear. Copy the .uf2 onto it (drag-and-drop).
5. The Pico will reboot automatically and the RPI-RP2 drive will disappear when flashing completes.

Tip: if you don’t see RPI-RP2, try a different USB cable (some are charge-only) or a different USB port/hub.

Flash alternatives: bootsel + drag-drop or picotool load. Flags:

• SWITCH_PICO_LOG: enable/disable UART logging on the Pico.

Changing controller colours

build.py can optionally update the grip colours in controller_color_config.h before building/flashing (default leaves the file unchanged):

• Random grip colours: python3 build.py --random-grip-color
• Set grip colours: python3 build.py --grip-color FF00AA

Python bridge (recommended)

Works on macOS, Windows, Linux. Uses SDL2 + pyserial.

Install dependencies (pyproject-enabled)

The repository now includes a pyproject.toml, so you can install the bridge and helper scripts as an editable package:

# from repo root
uv venv .venv
source .venv/bin/activate  # or .venv\Scripts\activate on Windows
uv pip install -e .

Prefer stock pip?

python -m venv .venv
source .venv/bin/activate  # or .venv\Scripts\activate on Windows
pip install -e .

• SDL2 runtime: install via your OS package manager (macOS: brew install sdl2; Windows: place SDL2.dll on PATH or next to the script; Linux: sudo apt install libsdl2-2.0-0 or equivalent).

Run

source .venv/bin/activate  # or .venv\Scripts\activate on Windows
controller-uart-bridge --interactive
# or, equivalently
python -m switch_pico_bridge.controller_uart_bridge --interactive

Options:

• --map index:PORT (repeatable) to pin controller index to serial (e.g., --map 0:/dev/cu.usbserial-0001 or --map 0:COM5).
• --ports PORTS... or --interactive for auto/interactive pairing.
• --all-ports to include non-USB serial devices in discovery.
• --ignore-port-desc SUBSTR / --include-port-desc SUBSTR to filter serial ports by description (repeatable).
• --include-controller-name SUBSTR to only open controllers whose name matches (repeatable).
• --list-controllers to print detected controllers and their GUIDs, then exit (useful for GUID-based options).
• --baud 921600 (default 921600; use 500000 if your adapter can’t do 900K).
• --frequency 1000 to send at 1 kHz.
• --deadzone 0.08 to change stick deadzone (0.0-1.0).
• --zero-sticks to sample the current stick positions on connect and treat them as neutral (cancel drift).
• --zero-hotkey z to choose the terminal hotkey that re-zeroes all connected controllers on demand (press z by default; pass an empty string to disable).
• --update-controller-db to download the latest SDL GameController database before launching (defaults to the bundled copy in switch_pico_bridge/controller_db/).
• --controller-db-url URL to override the source URL when updating the controller database (defaults to the official mdqinc repo).
• --trigger-threshold 0.35 to change analog trigger press threshold (0.0-1.0).
• --swap-abxy to flip AB/XY globally.
• --swap-abxy-index N (repeatable) to flip AB/XY for controllers first seen at index N (auto-converts to a stable GUID).
• --swap-abxy-guid GUID (repeatable) to flip AB/XY for a specific physical controller (GUID is stable across runs).
• --swap-hotkey x to pick the runtime hotkey that prompts you to toggle ABXY layout for a specific connected controller (default x; empty string disables).
• --sdl-mapping path/to/gamecontrollerdb.txt to load extra SDL mappings (defaults to switch_pico_bridge/controller_db/gamecontrollerdb.txt).

Runtime hotkeys

• By default, pressing z in the terminal re-samples every connected controller's sticks and re-applies neutral offsets. Change/disable with --zero-hotkey.
• Press x (configurable via --swap-hotkey) to open an in-CLI prompt and toggle the ABXY layout for a specific connected controller. This updates the controller's stable GUID list immediately; press again to revert.
• Hotkeys work only when the bridge is started from a TTY/console that currently has focus. Pass an empty string to either flag to disable that shortcut (useful when running unattended).
• If you launch the bridge with --swap-abxy (global swap), the per-controller toggle hotkey will show that the layout is enforced globally and will not override it.

Updating SDL controller mappings

• The bridge ships with a pinned switch_pico_bridge/controller_db/gamecontrollerdb.txt. Run controller-uart-bridge --update-controller-db ... to download the latest database from the official upstream (mdqinc/SDL_GameControllerDB).
• The download only touches switch_pico_bridge/controller_db/gamecontrollerdb.txt; add --controller-db-url https://.../custom.txt if you maintain your own fork.
• If the file is missing, the bridge will automatically attempt a download on startup.

Hot-plugging: controllers and UARTs can be plugged/unplugged while running; the bridge will auto reconnect when possible.

Using the lightweight UART helper (no SDL needed)

For simple scripts or tests you can skip SDL and drive the Pico directly with switch_pico_bridge.switch_pico_uart:

from switch_pico_bridge import SwitchUARTClient, SwitchButton, SwitchDpad

with SwitchUARTClient("/dev/cu.usbserial-0001") as client:
    client.press(SwitchButton.A)
    client.release(SwitchButton.A)
    client.move_left_stick(0.0, -1.0)  # push up
    client.set_hat(SwitchDpad.UP_RIGHT)
    print(client.poll_rumble())  # returns (left, right) amplitudes 0.0-1.0 or None

• SwitchButton is an IntFlag (bitwise friendly) and SwitchDpad is an IntEnum for the DPAD/hat values (alias SwitchHat remains for older scripts).
• The helper only depends on pyserial; SDL is not required.

macOS tips

• Ensure the USB‑serial adapter shows up (use /dev/cu.usb* for TX).
• Some controllers’ Guide/Home buttons are intercepted by macOS; using XInput/DInput mode or disabling Steam’s controller handling helps.

Windows tips

• Use COMx for ports (e.g., COM5). Auto‑detect lists COM ports.
• Ensure SDL2.dll is on PATH or alongside the script.

Linux tips

• You may need udev permissions for /dev/ttyUSB*//dev/ttyACM* (add user to dialout/uucp or use udev rules).

References

• GP2040-CE (controller firmware ecosystem): https://github.com/OpenStickCommunity/GP2040-CE
• nxbt (Switch controller research/tools): https://github.com/Brikwerk/nxbt
• Nintendo Switch Reverse Engineering notes: https://github.com/dekuNukem/Nintendo_Switch_Reverse_Engineering
• hid-nintendo driver reference: https://github.com/DanielOgorchock/linux/blob/ogorchock/drivers/hid/hid-nintendo.c

Troubleshooting

• No input on Switch: verify UART wiring (Pico GPIO4/5), baud matches both sides, Pico flashed with current firmware, and Pro Controller Wired Communication is enabled on the Switch.
• Constant buzzing rumble: the bridge filters small rumble payloads; ensure baud isn’t dropping bytes. Try lowering rumble scale in switch_pico_bridge.controller_uart_bridge if needed.
• Guide/Home triggers system menu (macOS): try different controller mode (XInput/DInput), disable Steam overlay/controller support, or connect wired.
• SDL can’t see controller: load switch_pico_bridge/controller_db/gamecontrollerdb.txt (default), add your own mapping, or try a different mode on the pad (e.g., XInput).