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Overview

The XInputBackend class provides XInput protocol support, allowing HayBox controllers to be recognized as Xbox 360 controllers on PC. This is the preferred backend for most PC games and emulators that support XInput.
XInput provides better compatibility with modern PC games compared to DInput, with native support for analog triggers and rumble.

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Platform Support

  • Raspberry Pi Pico: ✅ Supported
  • Arduino (AVR): ❌ Not supported

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Constructor

XInputBackend(
    InputState &inputs,
    InputSource **input_sources,
    size_t input_source_count
)
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inputs
InputState&
required
Reference to the global input state structure that tracks all button and analog input values.
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input_sources
InputSource**
required
Array of pointers to input source objects (GPIO buttons, analog sticks, etc.) that provide input data.
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input_source_count
size_t
required
Number of elements in the input_sources array.

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Key Features

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USB Device Identity

The backend configures the USB device to appear as:
  • Vendor ID: 0x0738 (Mad Catz)
  • Product ID: 0x4726 (Xbox 360 Controller)

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Button Mapping

XInput supports the following buttons:
  • Face buttons: A, B, X, Y
  • Shoulder buttons: LB, RB
  • Analog triggers: LT, RT (0-255)
  • D-pad: Up, Down, Left, Right
  • System buttons: Start, Back, Home
  • Stick clicks: LS, RS

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Analog Inputs

  • Left Stick: X/Y axes (16-bit signed)
  • Right Stick: X/Y axes (16-bit signed)
  • Triggers: LT/RT (8-bit unsigned, 0-255)

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Configuration

To use XInput as your primary backend, configure it in your device config: 
CommunicationBackendConfig backend_config = {
    .backend_id = COMMS_BACKEND_XINPUT,
};

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Backend ID

CommunicationBackendId BackendId() {
    return COMMS_BACKEND_XINPUT;
}
Returns COMMS_BACKEND_XINPUT to identify this backend type.

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SendReport Method

void SendReport();
The SendReport() method handles the complete input processing pipeline:
  1. Scans inputs at three different speeds (slow, medium, fast)
  2. Waits for XInput device to be ready
  3. Updates output state based on game mode logic
  4. Maps outputs to XInput report format
  5. Sends the report via USB

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Input Scanning

The backend uses a three-stage scanning approach:
  • SLOW: Updates infrequently-changing inputs
  • MEDIUM: Updates moderately responsive inputs
  • FAST: Updates after USB ready signal for minimal latency

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Usage Example

// In your config file
#include "comms/XInputBackend.hpp"

static InputState inputs;
static InputSource *input_sources[] = { &gpio_input };
size_t input_source_count = 1;

// Create the backend
XInputBackend xinput_backend(
    inputs,
    input_sources,
    input_source_count
);

void loop() {
    // Send controller state to PC
    xinput_backend.SendReport();
}

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Implementation Details

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Report Structure

The backend uses xinput_report_t which includes:
  • 16-bit signed values for stick axes
  • 8-bit unsigned values for analog triggers
  • Digital button states as boolean flags
  • D-pad directions as individual buttons

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Analog Conversion

Stick values are converted from 8-bit (0-255) to 16-bit signed (-32768 to 32767): 
_report.lx = (_outputs.leftStickX - 128) * 65535 / 255 + 128;
_report.ly = (_outputs.leftStickY - 128) * 65535 / 255 + 128;

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Trigger Handling

Analog triggers support both digital and analog modes:
  • If digital trigger is pressed: Reports 255 (full press)
  • Otherwise: Reports analog value (0-255)
The backend automatically handles Serial port management, closing and reopening it around XInput initialization.

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See Also

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