I know this isn't SO, but it's a fairly niche space and someone might be able to answer this

[rlewkowicz]

There is no bug template so I feel like this is fair game for visibility.

Discussed in #1499

^{Originally posted by rlewkowicz April 25, 2024}
TLDR: Is the 360 controller right joystick x/y 16 bits?

I dumped the report descriptor for a 360 controller and I'm still trying to understand what I'm looking at.

0x05, 0x01,        // Usage Page (Generic Desktop Ctrls)
0x09, 0x05,        // Usage (Game Pad)
0xA1, 0x01,        // Collection (Application)
0x09, 0x00,        //   Usage (Undefined)
0xA1, 0x00,        //   Collection (Physical)
0x09, 0x30,        //     Usage (X)
0x15, 0x00,        //     Logical Minimum (0)
0x35, 0x00,        //     Physical Minimum (0)
0x65, 0x00,        //     Unit (None)
0x55, 0x00,        //     Unit Exponent (0)
0x75, 0x10,        //     Report Size (16)
0x95, 0x01,        //     Report Count (1)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x09, 0x31,        //     Usage (Y)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0xC1, 0x00,        //   End Collection
0x09, 0x00,        //   Usage (Undefined)
0xA1, 0x00,        //   Collection (Physical)
0x09, 0x33,        //     Usage (Rx)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x09, 0x34,        //     Usage (Ry)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0xC1, 0x00,        //   End Collection
0x09, 0x00,        //   Usage (Undefined)
0xA1, 0x00,        //   Collection (Physical)
0x09, 0x32,        //     Usage (Z)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0xC1, 0x00,        //   End Collection
0x05, 0x09,        //   Usage Page (Button)
0x19, 0x01,        //   Usage Minimum (0x01)
0x29, 0x0A,        //   Usage Maximum (0x0A)
0x25, 0x01,        //   Logical Maximum (1)
0x45, 0x01,        //   Physical Maximum (1)
0x75, 0x01,        //   Report Size (1)
0x95, 0x0A,        //   Report Count (10)
0x81, 0x02,        //   Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x05, 0x01,        //   Usage Page (Generic Desktop Ctrls)
0x09, 0x39,        //   Usage (Hat switch)
0x15, 0x01,        //   Logical Minimum (1)
0x25, 0x08,        //   Logical Maximum (8)
0x46, 0x3B, 0x10,  //   Physical Maximum (4155)
0x65, 0x0E,        //   Unit (None)
0x75, 0x04,        //   Report Size (4)
0x95, 0x01,        //   Report Count (1)
0x81, 0x42,        //   Input (Data,Var,Abs,No Wrap,Linear,Preferred State,Null State)
0x15, 0x00,        //   Logical Minimum (0)
0x25, 0x01,        //   Logical Maximum (1)
0x45, 0x01,        //   Physical Maximum (1)
0x65, 0x00,        //   Unit (None)
0x75, 0x01,        //   Report Size (1)
0x95, 0x12,        //   Report Count (18)
0x81, 0x03,        //   Input (Const,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0xC1, 0x00,        // End Collection

// 107 bytes

// best guess: USB HID Report Descriptor

Right here is what I'm trying to figure out:

0x09, 0x33,        //     Usage (Rx)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x09, 0x34,        //     Usage (Ry)
0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)

Lets move the right joystick all the way up and actually look at the report that is sent:

00 14 00 00 00 00 00 00 00 00 a1 3f ff 7f 00 00 00 00 00 00

a1 3f ff 7f is our right joystick. Now I can decode a portion of this into 8 bits and get the expected -127/127 etc. But there's 2 other bits that move. So you'd think it's 16, but I think 30k is supposed to be the middle and in my testing it just doesn't line up right.

Can anyone tell me what a1 3f ff 7f is?