Welcome to the mbed-gamepad-drivers wiki!

(ECE - 4180 Final Project)

Team Members:

• Vineeth Voruganti
• Srikar Tallapragada
• Joshua Chang

Components

Mbed:

Sparkfun Pushbuttons:

Sparkfun Thumb Joystick:

Sparkfun USB Mini-B Breakout:

Wiring

Schematic:

Sparkfun Thumb Joystick:

Sparkfun USB Mini-B Breakout:

Pushbuttons:

Software

The software for this project is split between two parts: The driver code (USBGamepad.h and USBGamepad.cpp) and an example usage in main.cpp

Driver Code

HID drivers work by constantly sending a report to the host device with the state of the inputs in the device. The structure of this report has to be very explicitly defined with a descriptor. Below is the exact descriptor used in these drivers

{
    USAGE_PAGE(1),      0x01,       // Generic Desktop
    USAGE(1),           0x05,       // Gamepad
    COLLECTION(1),      0x01,       // Application
    COLLECTION(1),      0x00,       // Physical

    REPORT_COUNT(1),    0x06,       // 6 Buttons
    REPORT_SIZE(1),     0x01,       // 1 bit each
    USAGE_PAGE(1),      0x09,       // Buttons
    USAGE_MINIMUM(1),       0x01,   // Button #1 
    USAGE_MAXIMUM(1),       0x06,   // Button #6
    LOGICAL_MINIMUM(1),     0x00,   // Minimum = 0 
    LOGICAL_MAXIMUM(1),     0x01,   // Maximum = 1
    INPUT(1),           0x02,       // INPUT type TODO check this INPUT(data,var,abs)
    REPORT_COUNT(1),    0x01,       // Unused Bits for buttons
    REPORT_SIZE(1),     0x02,
    INPUT(1),           0x03,       // INPUT(Cnst,var,abs)

    REPORT_COUNT(1),    0x04,       // 4 Axies
    REPORT_SIZE(1),     0x08,       // 1 Byte Each 
    USAGE_PAGE(1),      0x01,       // Generic Desktop
    USAGE(1),           0x30,       // X
    USAGE(1),           0x31,       // Y
    USAGE(1),           0x32,       // Z
    USAGE(1),           0x33,       // Rx
    LOGICAL_MINIMUM(1),     0x81,   // Logical Minimum (-127)
    LOGICAL_MAXIMUM(1),     0x7f,   // Logical Maximum (127)
    INPUT(1),           0x02,       // Relative data INPUT(data,var,abs)

    END_COLLECTION(0),
    END_COLLECTION(0),
};

This descriptor was made using the USB reference tables on the USB specification website.

It describes a device meant for a general desktop, that acts as a gamepad with 6 buttons and 4 axies of control.

This driver code is defined in USBGamepad.h and USBGamepad.cpp. The constructor defines a generic USB HID device and connects to the host device. The gamepad_send() method is used to send the reports to the host device.

Below are some reference links that assisted us in making the descriptor

• Custom HID Controller with a Teensy
• Arduino SNES Controller

Example

The example code itself is a sample implementation that utilizes the driver code with our hardware peripherals. Our hardware had 6 buttons including the ones in the sparkfun joysticks and 4 axies of control. The main.cpp file initalizes a gamepad instance and all other relevant hardware peripherals.

The main block contains a while loop that continuously polls the state of the hardware and sends it to the host device via the update() method of the gamepad

Summary of results

The final result of this project was a perfectly working HID controller that works on a windows 10 laptop. This was tested using both the joy.cpl and the video game Zero ranger.

Future Works

Currently, the drivers are hardcoded for the hardware we designed, but in the future, it could be made more generalized by passing in a custom report descriptor to the constructor.