embedded config_error ai_generated partial

USB HID: Report descriptor too large, max allowed 64 bytes but descriptor size is 128 bytes

ID: embedded/usb-hid-report-descriptor-too-large

Also available as: JSON · Markdown · 中文
78%Fix Rate
83%Confidence
1Evidence
2024-06-19First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
STM32 USB Device Library 2.6.0 active — — —
TinyUSB 0.16.0 active — — —
ARM GCC 12.2.1 active — — —

Root Cause

USB HID report descriptor exceeds the maximum size defined in device configuration descriptor (bMaxPacketSize0), typically 64 bytes for full-speed devices.

generic

中文

USB HID 报告描述符超过设备配置描述符中定义的最大大小（bMaxPacketSize0），对于全速设备通常为 64 字节。

Official Documentation

https://www.usb.org/document-library/hid-usage-tables-112

Workarounds

  1. 85% success Compress report descriptor by using short items (e.g., replace INPUT(Data,Var,Abs) with INPUT(Const) for unused fields) and remove redundant usage pages. Example: replace multiple 4-byte items with 2-byte short forms. 
    Compress report descriptor by using short items (e.g., replace INPUT(Data,Var,Abs) with INPUT(Const) for unused fields) and remove redundant usage pages. Example: replace multiple 4-byte items with 2-byte short forms.
  2. 75% success Switch to high-speed USB mode if hardware supports it (bMaxPacketSize0 = 512 bytes). Update device descriptor: bcdUSB = 0x0200 and configure PHY for HS. This allows larger report descriptors up to 512 bytes. 
    Switch to high-speed USB mode if hardware supports it (bMaxPacketSize0 = 512 bytes). Update device descriptor: bcdUSB = 0x0200 and configure PHY for HS. This allows larger report descriptors up to 512 bytes.

中文步骤

  1. Compress report descriptor by using short items (e.g., replace INPUT(Data,Var,Abs) with INPUT(Const) for unused fields) and remove redundant usage pages. Example: replace multiple 4-byte items with 2-byte short forms.
  2. Switch to high-speed USB mode if hardware supports it (bMaxPacketSize0 = 512 bytes). Update device descriptor: bcdUSB = 0x0200 and configure PHY for HS. This allows larger report descriptors up to 512 bytes.

Dead Ends

Common approaches that don't work:

  1. Increase bMaxPacketSize0 in USB descriptor to 128 bytes 85% fail

    bMaxPacketSize0 is limited by USB specification (64 bytes for full-speed, 512 for high-speed); increasing beyond spec causes host rejection.

  2. Split report descriptor across multiple endpoints 90% fail

    HID class does not support multi-packet report descriptors; descriptor must fit in one control transfer.