demonstrate odd usb.core.USBError with max3421e, circuitpython

!midi_host_issue.py

# demonstrate odd usb.core.USBError with max3421e
# requires "adafruit_usb_host_midi_todbot" below, which adds timeout on read()s
# 12 May 2024 - @todbot
import displayio
displayio.release_displays()

import time
import board
import usb
import max3421e

import adafruit_usb_host_midi_todbot as adafruit_usb_host_midi

spi = board.SPI()
cs = board.D10
irq = board.D9

host_chip = max3421e.Max3421E(spi, chip_select=cs, irq=irq)

host_timeout = 0.001

while True:
   midi_usb_device = None
   for device in usb.core.find(find_all=True):
      try:
         midi_usb_device = adafruit_usb_host_midi.MIDI(device, host_timeout)
         print("Found vid/pid %04x/%04x" % (device.idVendor, device.idProduct),
               device.manufacturer, device.product)
      except ValueError:
         print("bad device:", device)

      while True:
         print(time.monotonic(), "UI task, should print continuously")
         time.sleep(0.1)
         b = midi_usb_device.read(1)
         if b:
            print("b:",b)

adafruit_usb_host_midi_todbot.py

# SPDX-FileCopyrightText: Copyright (c) 2023 Scott Shawcroft for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""
`adafruit_usb_host_midi`
================================================================================

CircuitPython USB host driver for MIDI devices


* Author(s): Scott Shawcroft
"""

import usb.core
import adafruit_usb_host_descriptors

__version__ = "0.0.0+auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_USB_Host_MIDI.git"


DIR_IN = 0x80

class MIDI:
    def __init__(self, device, timeout=None):
        self.interface_number = 0
        self.in_ep = 0
        self.out_ep = 0
        self.device = device
        self.timeout_ms = round(timeout * 1000) if timeout else 0

        self.buf = bytearray(64)
        self.start = 0
        self._remaining = 0

        config_descriptor = adafruit_usb_host_descriptors.get_configuration_descriptor(
            device, 0
        )

        i = 0
        midi_interface = False
        while i < len(config_descriptor):
            descriptor_len = config_descriptor[i]
            descriptor_type = config_descriptor[i + 1]
            if descriptor_type == adafruit_usb_host_descriptors.DESC_CONFIGURATION:
                config_value = config_descriptor[i + 5]
            elif descriptor_type == adafruit_usb_host_descriptors.DESC_INTERFACE:
                interface_number = config_descriptor[i + 2]
                interface_class = config_descriptor[i + 5]
                interface_subclass = config_descriptor[i + 6]
                midi_interface = interface_class == 0x1 and interface_subclass == 0x3
                if midi_interface:
                    self.interface_number= interface_number

            elif descriptor_type == adafruit_usb_host_descriptors.DESC_ENDPOINT:
                endpoint_address = config_descriptor[i + 2]
                if endpoint_address & DIR_IN:
                    if midi_interface:
                        self.in_ep = endpoint_address
                else:
                    if midi_interface:
                        self.out_ep = endpoint_address
            i += descriptor_len

        device.set_configuration()
        device.detach_kernel_driver(self.interface_number)

    def read(self, size):
        if self._remaining == 0:
            try:
                n = self.device.read(self.in_ep, self.buf, self.timeout_ms)
                self._remaining = n - 1
                self.start = 1
            except usb.core.USBTimeoutError as e:
                print("timeout error:",e)
                pass
        size = min(size, self._remaining)
        b = self.buf[self.start:self.start + size]
        self.start += size
        self._remaining -= size
        return b

    def readinto(self, buf):
        b = self.read(len(buf))
        n = len(b)
        if n:
            buf[:] = b
        return n

    def __repr__(self):
        # also idProduct/idVendor for vid/pid
        return "MIDI Device " + str(self.device.manufacturer) + "/" + str(self.device.product)

But when run, this code sees one usb.core.USBTimeoutError and then errors out with a usb.core.USBError:

Auto-reload is on. Simply save files over USB to run them or enter REPL to disable.
code.py output:
Found vid/pid 1c75/0288 Arturia Arturia KeyStep 32
705.569 UI task, should print continuously
timeout error: 
705.683 UI task, should print continuously
Traceback (most recent call last):
  File "code.py", line 35, in <module>
  File "adafruit_usb_host_midi_todbot.py", line 70, in read
usb.core.USBError: 

Code done running.

Not (necessarily) related, but the code starting at line 41 in your adafruit_usb_host_midi_todbot.py

        while i < len(config_descriptor):
            descriptor_len = config_descriptor[i]
            ...
            i += descriptor_len

is problematic when the descriptor is returned with nulls (zeros) as I have seen. Yes, I know, it shouldn't be all null, but it sometimes is - and then the above code loops forever (cuz the len is zero and it gets stuck there).

Just sayin'.

And this code is still in the library itself. :-/