Feather rp2040 with USB Type A - crashes when connecting keyboards

[scrambler803]

Description

I'm trying to use a USB keyboard with the Feather RP2040 with USB Type A in CircuitPython (version 9.2.4). However, when I plug in my keyboards, the Feather crashes and disconnects from the PC after about 15 seconds.

I tested using Adafruit’s USB Host device info example, and the behavior is consistent. A wired USB mouse works fine and is detected correctly, but both keyboards I tested cause the Feather to crash.

Keyboards Tested

1. Apple USB Keyboard (with built-in USB hub and media keys)
2. Custom keyboard running QMK firmware on a Raspberry Pi Pico

Troubleshooting Steps Taken

• Plugging in a wired USB mouse works fine, with proper enumeration output.
• Tested with KMK firmware instead of QMK—same crash.
• Verified the Feather RP2040 board is powered (green LED on).
• Attempted listing USB devices using a modified device_info.py script but the Feather crashes upon keyboard connection.
• Tried flashing an experimental firmware build provided in Discord—still crashes.
• Suspected composite USB devices (e.g., keyboards with extra media keys) might be the issue, but not confirmed.
• A developer (tannewt) was able to reproduce the crash with a Mac keyboard.

• Additional Troubleshooting with QMK Firmware

  • To rule out compatibility issues, I attempted modifying the QMK firmware on my custom keyboard to ensure it enumerates as a single, basic HID device rather than a composite device.

  • Changes attempted in rules.mk:

    make
    Copy
    Edit
    NKRO_ENABLE = no
    EXTRAKEY_ENABLE = no
    CONSOLE_ENABLE = no
    MOUSEKEY_ENABLE = no
    KEYBOARD_SHARED_EP = no  # Previously set to "yes"
    

  • Despite these changes, the keyboard still causes the Feather to crash when connected.

  • Key insight from QMK developers:

    • Setting KEYBOARD_SHARED_EP = no should have forced the keyboard to enumerate as a basic 6KRO HID device.
    • Even after doing this, the Feather still crashes upon connection.
    • This suggests the issue may not be related to composite vs. single USB device enumeration but rather a deeper incompatibility between certain HID keyboards and the Feather’s USB host implementation.

Expected Behavior

The Feather should enumerate the keyboard as a USB device and allow input handling, similar to how it correctly detects a mouse.

Actual Behavior

• Upon connecting a keyboard, the Feather freezes for about 15 seconds, then crashes and disconnects from the PC.
• Issue occurs even without running code.py—the Feather crashes just from plugging in the keyboard.

CircuitPython Version

• Firmware: adafruit-circuitpython-adafruit_feather_rp2040_usb_host-en_US-9.2.4.uf2

Possible Causes?

• Incompatibility with composite USB devices (keyboards with multiple endpoints for media keys, hubs, etc.).
• TinyUSB limitations in handling certain keyboard USB descriptors.
• Insufficient power or USB negotiation issues with the Feather RP2040.

Additional Context

tannewt suggested that USB enumeration failures might be causing the crash, and Thach (who works on TinyUSB) might be able to look into it.

Would appreciate any insights on what types of keyboards are supported and whether this is a known issue with TinyUSB on the Feather RP2040.

[tannewt]

I was able to reproduce this on the USB host feather wing but not on the RP2040 feather with a usb host breakout cable plugged in. The breakout cable's power pin was connected to the USB power pin on the feather header.

I suspect a power issue because the crash doesn't result in a safe mode. The device disappears and doesn't come back. I mean to check my Linux dmesg output but have run out of time. I'd also check the USB activity with an analyzer to see if anything happens before the crash. If nothing does, then power is a likely cause.