Pico 2 host_device_info enumerates nothing after some warm resets

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
18/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
arduino, c, raspberry-pi
Domain
embedded-iot

Research direction

Start with examples/Host/Simple/host_device_info/host_device_info.ino, specifically the print_device_descriptor callback and its tuh_descriptor_get_*_string_sync() calls, and check the ignored USBHost.begin() return value. Compare against tinyusb's examples/host/device_info. Done means a reproducible cause for devices missing after warm resets on Pico 2, confirmed by repeated resets with the console open, and a fix that enumerates both devices every time.

Written by the indexing model from the issue text.

Description

follow-up

On the ci.lan farm's Raspberry Pi Pico 2, examples/Host/Simple/host_device_info (native host, FQBN
rp2040:rp2040:rpipico2:...,usbstack=tinyusb_host, rp2040 core 5.4.3) intermittently enumerates nothing after a warm
reset. The console prints the banner and then no Device attached line for the whole capture. The attached devices
are a General UDisk (abcd:1234) and a CH340 (1a86:7523).

Observed

  • HIL battery, roster commit b62b97e (library master, vendored TinyUSB dcd2a4bd0), two runs: host_device_info
    failed on the test pass (reported [], 32.4 s) and passed on the cleanup pass, which runs the same step, flash
    included.
  • Again in #619's run ard-registry-host-1 at 998752d (devices read from agentrc's board registry): test pass
    reported [] (32.4 s), cleanup pass [('abcd:1234', '\u0409')]. Pico W passed on the same run.
  • Manual session, hil_remote.py session exec <id> console --seconds 12 --reset (probe reset with the console open):
    • master firmware: devices enumerated on 1 of 4 resets;
    • firmware at #615's head 553c732 (TinyUSB d543126c5) plus the roster commit: enumerated on resets 2, 4 and 6,
      never on 1, 3, 5 or 7.
  • tinyusb's own host examples (device_info, msc_file_explorer, cdc_msc_hid) enumerated both devices on every
    flash in three farm runs on the same board and port.

The Pico 2's previous Kingston stick showed a similar failure on 2026-11-02 (HIL contract, Recovery).

Not established

The cause is not isolated: the library, the rp2040 core's host startup, the reset procedure and the devices' response
to a reset without a VBUS cycle all remain candidates. Source leads, unverified:

  • host_device_info.ino calls tuh_descriptor_get_*_string_sync() from the print_device_descriptor transfer
    callback, inside the host task; tinyusb's current examples/host/device_info defers those reads out of the callback.
    This matters once a device is attached, so it does not explain a missing Device attached.
  • The sketch ignores USBHost.begin()'s return value, so an initialisation failure would be silent.

Remaining work

  • Capture a failing reset on the wire (usb-sniffer on the Pico 2's host port) or with host-stack logging
    (CFG_TUSB_DEBUG) to see whether the bus reset, the first GET_DESCRIPTOR or the root-port connect detection fails.
  • Compare with tinyusb's device_info built for the same board under the same reset command.
  • Until fixed, the Arduino HIL host_device_info result on Pico 2 depends on the reset count.

Surfaced while replacing the Pico 2's thumb drive: #615, #619.

Dominant language
C
Stars
654
Forks
187
Avg merge
21h 1m
Merged PRs (30d)
17

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