UART Output Interface

Sends controller input events over UART serial to an external microcontroller. Designed for bridging USB/BT controller inputs to devices like ESP32-S3 (for AI processing), another Joypad board, or any external MCU that needs controller state.

Protocol

• Wire protocol: UART serial with framed binary packets
• PIO programs: None (uses hardware UART peripheral)
• Core: Runs on Core 0 (not timing-critical)
• Default baud rate: 115200
• Packet format: Type byte + payload + length framing (defined in core/uart/uart_protocol.h)

The UART device and host (uart_host) can share the same UART peripheral for bidirectional communication -- controller events go out, feedback commands (rumble, LEDs) come in.

GPIO Pins

Signal	GPIO	Notes
TX	GP4	Default (Qwiic cable SDA position)
RX	GP5	Default (Qwiic cable SCL position)

Pins are configurable at init time via uart_device_init_pins().

Player Support

• Max players: 1 (single stream of merged input events)

Operating Modes

Mode	Constant	Description
Off	UART_DEVICE_MODE_OFF	UART device disabled
Stream	UART_DEVICE_MODE_STREAM	Send all input events continuously
On Change	UART_DEVICE_MODE_ON_CHANGE	Only send when state changes
On Request	UART_DEVICE_MODE_ON_REQUEST	Only send when remote requests

Button Mapping

Input events are transmitted in the universal input_event_t format. No console-specific button translation is performed -- the remote device receives JP_BUTTON_* constants directly and performs its own mapping.

Analog Mapping

All 8 analog axes from input_event_t are transmitted as-is (0-255, 128 = center).

Feedback

The UART device supports bidirectional feedback from the remote MCU:

• Rumble: Remote can send rumble commands (player index, left/right motor intensity, duration). Delivered via registered callback (uart_device_set_rumble_callback).
• LED: Remote can send LED commands (player index, pattern, RGB color). Delivered via registered callback (uart_device_set_led_callback).

Connection Events

The UART device sends player connect/disconnect notifications: - uart_device_send_connect() -- player connected with device type, VID/PID - uart_device_send_disconnect() -- player disconnected

Diagnostics

Statistics available via API: - TX/RX packet counts - Error count - Queue drop count (events dropped when TX queue full) - Connection status (true if valid packet received recently)

Profiles

No profiles. Button mapping is passed through unchanged.

Apps Using This Output

App	Description
usb2uart	USB controllers to UART serial bridge