CODEWITHSUNDEEP
usbhidfirmwaredescriptorgamepad
Retro Tec
Retro Tec

Reputation: 1

how to capture HID hex button codes for usb gamepad

Hi I have some firmware I want to modify that reads from USB gamepads, I want to edit the firmware for my own gamepad

I assume these hex codes refer to up down left right and buttons on the gamepad, this gamepad is a cheap nonbranded one detected as a Dragon rise chip in windows

0x11,0x40,0x21,0xC0,0x10,0x40,0x20,0xC0,0x36,0xFF

I need to find the correct set of 10 hex codes for a different Logitech USB gamepad, is there an easy way to find this in windows?

I have tried using hid capture program but the hex dump has lots of sets of hex codes and I don't know how to identify the buttons or directions

Upvotes: 0

Views: 648

Answers (1)

nondebug
nondebug

Reputation: 1011

You need to get the report descriptor and parse it to understand how button and axis values are represented in the input report. The report descriptor format is documented in the Device Class Definition for HID.

D-pad inputs are almost always represented as a rotational axis. I have a Logitech F310 and it represents the D-pad as a 4-bit value in the lower bits of the 5th byte:

80 7F 80 7F 00 00 00 FF  // Holding up
80 7F 80 7F 01 00 00 FF  // Holding up + right
80 7F 80 7F 02 00 00 FF  // Holding right
80 7F 80 7F 03 00 00 FF  // Holding down + right
80 7F 80 7F 04 00 00 FF  // Holding down
80 7F 80 7F 05 00 00 FF  // Holding down + left
80 7F 80 7F 06 00 00 FF  // Holding left
80 7F 80 7F 07 00 00 FF  // Holding up + left
80 7F 80 7F 08 00 00 FF  // Not holding any direction

Note how the value increases as we move clockwise around the D-pad. There's a special value for the "not holding any direction" state.

Upvotes: 1

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