It's impossible to modify joystick hid reports to working state.

[MalwareX95]

Hello. I''ve created this issue because I found out impossible to modify those descriptors without issues with either pipe stalling errors or not recognizing joystick at all.

I'm working on windows 11, teeny core 1.59.0 with teensy 4.1 board.

lets take this descriptor for example from usb_desc.c. Just lets add another slider here its report size is 10 bits so we need two additional bytes so its 14 bytes in total where original report descriptor has 12 bytes for inputs.

that's mine modified

static uint8_t joystick_report_desc[] = {
        0x05, 0x01,                     // Usage Page (Generic Desktop)
        0x09, 0x04,                     // Usage (Joystick)
        0xA1, 0x01,                     // Collection (Application)
        0x15, 0x00,                     //   Logical Minimum (0)
        0x25, 0x01,                     //   Logical Maximum (1)
        0x75, 0x01,                     //   Report Size (1)
        0x95, 0x20,                     //   Report Count (32)
        0x05, 0x09,                     //   Usage Page (Button)
        0x19, 0x01,                     //   Usage Minimum (Button #1)
        0x29, 0x20,                     //   Usage Maximum (Button #32)
        0x81, 0x02,                     //   Input (variable,absolute)
        0x15, 0x00,                     //   Logical Minimum (0)
        0x25, 0x07,                     //   Logical Maximum (7)
        0x35, 0x00,                     //   Physical Minimum (0)
        0x46, 0x3B, 0x01,               //   Physical Maximum (315)
        0x75, 0x04,                     //   Report Size (4)
        0x95, 0x01,                     //   Report Count (1)
        0x65, 0x14,                     //   Unit (20)
        0x05, 0x01,                     //   Usage Page (Generic Desktop)
        0x09, 0x39,                     //   Usage (Hat switch)
        0x81, 0x42,                     //   Input (variable,absolute,null_state)
        0x05, 0x01,                     //   Usage Page (Generic Desktop)
        0x09, 0x01,                     //   Usage (Pointer)
        0xA1, 0x00,                     //   Collection ()
        0x15, 0x00,                     //     Logical Minimum (0)
        0x26, 0xFF, 0x03,             //     Logical Maximum (1023)
        0x75, 0x0A,                     //     Report Size (10)
        0x95, 0x04,                     //     Report Count (4)
        0x09, 0x30,                     //     Usage (X)
        0x09, 0x31,                     //     Usage (Y)
        0x09, 0x32,                     //     Usage (Z)
        0x09, 0x35,                     //     Usage (Rz)
        0x81, 0x02,                     //     Input (variable,absolute)
        0xC0,                              //   End Collection
        0x15, 0x00,                     //   Logical Minimum (0)
        0x26, 0xFF, 0x03,            //   Logical Maximum (1023)
        0x75, 0x0A,                     //   Report Size (10)
        0x95, 0x03,                     //   Report Count (3) ; original value 0x95, 0x02
        0x09, 0x36,                     //   Usage (Slider)
        0x09, 0x36,                     //   Usage (Slider)
        0x09, 0x36,                     //   Usage (Slider); added by me 
        0x81, 0x02,                     //   Input (variable,absolute)
        0xC0                            // End Collection
};

that's desc. from library

static uint8_t joystick_report_desc[] = {
        0x05, 0x01,                     // Usage Page (Generic Desktop)
        0x09, 0x04,                     // Usage (Joystick)
        0xA1, 0x01,                     // Collection (Application)
        0x15, 0x00,                     //   Logical Minimum (0)
        0x25, 0x01,                     //   Logical Maximum (1)
        0x75, 0x01,                     //   Report Size (1)
        0x95, 0x20,                     //   Report Count (32)
        0x05, 0x09,                     //   Usage Page (Button)
        0x19, 0x01,                     //   Usage Minimum (Button #1)
        0x29, 0x20,                     //   Usage Maximum (Button #32)
        0x81, 0x02,                     //   Input (variable,absolute)
        0x15, 0x00,                     //   Logical Minimum (0)
        0x25, 0x07,                     //   Logical Maximum (7)
        0x35, 0x00,                     //   Physical Minimum (0)
        0x46, 0x3B, 0x01,               //   Physical Maximum (315)
        0x75, 0x04,                     //   Report Size (4)
        0x95, 0x01,                     //   Report Count (1)
        0x65, 0x14,                     //   Unit (20)
        0x05, 0x01,                     //   Usage Page (Generic Desktop)
        0x09, 0x39,                     //   Usage (Hat switch)
        0x81, 0x42,                     //   Input (variable,absolute,null_state)
        0x05, 0x01,                     //   Usage Page (Generic Desktop)
        0x09, 0x01,                     //   Usage (Pointer)
        0xA1, 0x00,                     //   Collection ()
        0x15, 0x00,                     //     Logical Minimum (0)
        0x26, 0xFF, 0x03,               //     Logical Maximum (1023)
        0x75, 0x0A,                     //     Report Size (10)
        0x95, 0x04,                     //     Report Count (4)
        0x09, 0x30,                     //     Usage (X)
        0x09, 0x31,                     //     Usage (Y)
        0x09, 0x32,                     //     Usage (Z)
        0x09, 0x35,                     //     Usage (Rz)
        0x81, 0x02,                     //     Input (variable,absolute)
        0xC0,                           //   End Collection
        0x15, 0x00,                     //   Logical Minimum (0)
        0x26, 0xFF, 0x03,               //   Logical Maximum (1023)
        0x75, 0x0A,                     //   Report Size (10)
        0x95, 0x02,                     //   Report Count (2)
        0x09, 0x36,                     //   Usage (Slider)
        0x09, 0x36,                     //   Usage (Slider)
        0x81, 0x02,                     //   Input (variable,absolute)
        0xC0                            // End Collection
};

So next step would be to increase this number in usb_desc.h for USB_HID (I'm using keyboard + mouse + joystick).

#elif defined(USB_HID)
  #define VENDOR_ID		0x16C0
  #define PRODUCT_ID		0x0482
  #define MANUFACTURER_NAME	{'T','e','e','n','s','y','d','u','i','n','o'}
  #define MANUFACTURER_NAME_LEN	11
  #define PRODUCT_NAME		{'K','e','y','b','o','a','r','d','/','M','o','u','s','e','/','J','o','y','s','t','i','c','k'}
  #define PRODUCT_NAME_LEN	23
  #define EP0_SIZE		64
  #define NUM_ENDPOINTS         6
  #define NUM_USB_BUFFERS	24
  #define NUM_INTERFACE		5
  #define SEREMU_INTERFACE      2	// Serial emulation
  #define SEREMU_TX_ENDPOINT    2
  #define SEREMU_TX_SIZE        64
  #define SEREMU_TX_INTERVAL    1
  #define SEREMU_RX_ENDPOINT    2
  #define SEREMU_RX_SIZE        32
  #define SEREMU_RX_INTERVAL    2
  #define KEYBOARD_INTERFACE    0	// Keyboard
  #define KEYBOARD_ENDPOINT     3
  #define KEYBOARD_SIZE         8
  #define KEYBOARD_INTERVAL     1
  #define KEYMEDIA_INTERFACE    4	// Keyboard Media Keys
  #define KEYMEDIA_ENDPOINT     4
  #define KEYMEDIA_SIZE         8
  #define KEYMEDIA_INTERVAL     4
  #define MOUSE_INTERFACE       1	// Mouse
  #define MOUSE_ENDPOINT        5
  #define MOUSE_SIZE            8
  #define MOUSE_INTERVAL        1
  #define JOYSTICK_INTERFACE    3	// Joystick
  #define JOYSTICK_ENDPOINT     6
  #define JOYSTICK_SIZE         14	//  12 = normal, 64 = extreme joystick
  #define JOYSTICK_INTERVAL     2
  #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT3_CONFIG	ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT4_CONFIG	ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT5_CONFIG	ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
  #define ENDPOINT6_CONFIG	ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT

Such small change results in not sending packets at all and even not recognizing joystick in joy.cpl.

To verify if data are send I'm using this code and dumping packets via usbpcap
void loop() { Joystick.send_now(); delay(50); }