我的电脑时,PyUsb无法识别我的USB设备

Question

我正在尝试在我的PC和PIC18F4550之间进行通信,但是程序没有检测到它,而计算机正在设备管理器中显示它.

import usb.core

dev = usb.core.find(idVendor = 0x04D8, idProduct = 0xFEAA)

检查USB设备的功能:

def find(find_all = False, backend = None, custom_match = None, **args):
    def device_iter(k, v):
        for dev in backend.enumerate_devices():
            d = Device(dev, backend)
            if  _interop._reduce(lambda a, b: a and b,map(operator.eq,v,map(lambda i:getattr(d,i),k)),True)and (custom_match is None or custom_match(d)):
                yield d
        if backend is None:
            import usb.backend.libusb1 as libusb1
            import usb.backend.libusb0 as libusb0
            import usb.backend.openusb as openusb

            for m in (libusb1, openusb, libusb0):
                backend = m.get_backend()
                if backend is not None:
                    _logger.info('find(): using backend "%s"', m.__name__)
                       break
                 else:
                    raise ValueError('No backend available')

        k, v = args.keys(), args.values()

        if find_all:
            return device_iter(k, v)
        else:
            try:
                return _interop._next(device_iter(k, v))
            except StopIteration:
                return None

我在运行代码时遇到的错误.

Traceback (most recent call last):
 File "C:\modules\motor.py", line 29, in <module>
   dev = usb.core.find(idVendor=0x04D8,idProduct=0xFEAA)
 File "C:\Python27\lib\site-packages\usb\core.py", line 1199, in find
   raise ValueError('No backend available')
 ValueError: No backend available

在它用于正常执行之前,但在过去几天它显示此错误.我不明白突然发生了什么.使用PyUSB模块有什么问题吗？

我看到他们中的一些人在使用USB通信时遇到了同样的问题.

---

我已经解决了这个问题.解决方案是PyUSB模块将搜索libusb0.dll和libusb-1.0.dll文件,这些文件是与我们需要包含在PATH环境变量中的USB设备进行通信的后端.

Answer 1

PATH environment variable每当我们使用 PyUSB 模块与 PC 进行 USB 通信时，PyUSB 模块都会检查和位置中的 libusb0.dll 和 libusb-1.0.dll 文件（充当后端）C:\windows\System32，然后建立与 USB 设备的通信。由于我使用 libusb-win32-wizard 创建设备驱动程序，因此它使用 libusb0.dll。使用以下DEBUG程序可以看到执行过程：

import os
os.environ['PYUSB_DEBUG'] = 'debug'
import usb.core
print list(usb.core.find(find_all=True))

当我在Shell中执行上述程序时，我得到的输出是：

2016-03-26 11:41:44,280 ERROR:usb.libloader:'Libusb 1' could not be found
2016-03-26 11:41:44,280 ERROR:usb.backend.libusb1:Error loading libusb 1.0 backend
2016-03-26 11:41:44,280 ERROR:usb.libloader:'OpenUSB library' could not be found
2016-03-26 11:41:44,280 ERROR:usb.backend.openusb:Error loading OpenUSB backend
2016-03-26 11:41:44,280 INFO:usb.core:find(): using backend "usb.backend.libusb0"
2016-03-26 11:41:44,280 DEBUG:usb.backend.libusb0:_LibUSB.enumerate_devices()
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E530>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E5D0>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E6C0>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E7B0>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E8A0>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200E990>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200EA80>)
2016-03-26 11:41:44,296 DEBUG:usb.backend.libusb0:_LibUSB.get_device_descriptor(<usb.backend.libusb0._usb_device object at 0x0200EB70>)
[<DEVICE ID 046d:c05a on Bus 000 Address 001>, <DEVICE ID 046d:c31d on Bus 000 Address 002>, <DEVICE ID 046d:c31d on Bus 000 Address 003>, <DEVICE ID 046d:c31d on Bus 000 Address 004>, <DEVICE ID 04d8:feaa on Bus 000 Address 005>, <DEVICE ID 046d:082b on Bus 000 Address 006>, <DEVICE ID 046d:082b on Bus 000 Address 007>, <DEVICE ID 046d:082b on Bus 000 Address 008>]

find_all=True所以在这里，因为我在函数中给出了参数，所以usb.core.find()它返回连接到 PC 的每个设备 ID。另外，在前 4 行中，它给出了错误，因为我们使用 lib-usb-win32-wizard，它使用了 libusb0.dll，因此在第 5 行中它给出了错误，INFO:usb.core:find(): using backend "usb.backend.libusb0"这意味着它正在使用 libusb0.dll 与 USB 设备进行通信。