Mbed (Giga R1) USB HID FFB (PID) Report Descriptor Help

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1

I am currently developing a custom Giga R1 WiFi racing sim project for BeamNG.drive. Currently, my joystick inputs are fully functional and responding correctly, but I am having significant difficulties implementing Force Feedback (FFB).

Specifically, I am struggling to interpret the example descriptor (pid1_01, ~pg. 30) and adapt it to my own needs (I need Constant Force, Damper, Friction, & Inertia effect types, of which Friction is not even defined in the document).

I have attempted to generate descriptors using Waratah , but it hasn’t proved to be that useful because my challenge is not generating a syntactically correct descriptor, but understanding where to start, and how to structure & test it.

Here is my current joystick report descriptor:

0x05, 0x01,          // UsagePage(Generic Desktop[0x0001])
    0x09, 0x04,          // UsageId(Joystick[0x0004])
    0xA1, 0x01,          // Collection(Application)
    0x85, 0x01,          //     ReportId(1)
    0x09, 0x30,          //     UsageId(X[0x0030])
    0x15, 0x81,          //     LogicalMinimum(-127)
    0x25, 0x7F,          //     LogicalMaximum(127)
    0x95, 0x01,          //     ReportCount(1)
    0x75, 0x08,          //     ReportSize(8)
    0x81, 0x02,          //     Input(Data, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x05, 0x02,          //     UsagePage(Simulation Controls[0x0002])
    0x09, 0xBB,          //     UsageId(Throttle[0x00BB])
    0x09, 0xBA,          //     UsageId(Rudder[0x00BA])
    0x95, 0x02,          //     ReportCount(2)
    0x81, 0x02,          //     Input(Data, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x05, 0x01,          //     UsagePage(Generic Desktop[0x0001])
    0x09, 0x31,          //     UsageId(Y[0x0031])
    0x95, 0x01,          //     ReportCount(1)
    0x81, 0x02,          //     Input(Data, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x09, 0x39,          //     UsageId(Hat Switch[0x0039])
    0x46, 0x3B, 0x01,    //     PhysicalMaximum(315)
    0x65, 0x14,          //     Unit('degrees', EnglishRotation, Degrees:1)
    0x15, 0x00,          //     LogicalMinimum(0)
    0x25, 0x07,          //     LogicalMaximum(7)
    0x75, 0x03,          //     ReportSize(3)
    0x81, 0x02,          //     Input(Data, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x75, 0x04,          //     ReportSize(4)
    0x81, 0x03,          //     Input(Constant, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x05, 0x09,          //     UsagePage(Button[0x0009])
    0x19, 0x01,          //     UsageIdMin(Button 1[0x0001])
    0x29, 0x20,          //     UsageIdMax(Button 32[0x0020])
    0x45, 0x00,          //     PhysicalMaximum(0)
    0x65, 0x00,          //     Unit(None)
    0x25, 0x01,          //     LogicalMaximum(1)
    0x95, 0x20,          //     ReportCount(32)
    0x75, 0x01,          //     ReportSize(1)
    0x81, 0x02,          //     Input(Data, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0x95, 0x01,          //     ReportCount(1)
    0x81, 0x03,          //     Input(Constant, Variable, Absolute, NoWrap, Linear, PreferredState, NoNullPosition, BitField)
    0xC0,                // EndCollection()

The mappings are:

X —> Steering (-127, 127)
Y —> Clutch Pedal (-127, 127)
Throttle —> Gas Pedal (-127, 127 : but only 0 - 127 is used)
Rudder —> Brake Pedal (-127, 127 : but only 0 - 127 is used)
HAT + 32 Buttons —> Custom H-pattern/Sequential Setup (+ accessories)

Please, feel free to ask for clarification!
2

This is a bit in the weeds, but after consulting the AI overlords I have a suggested plan for ya: Kimi | FFB Descriptor Development Guide

I love Beam.NG! I have a cockpit and homemade direct-drive wheel + modified logitech pedals and a Quest3 :slight_smile: