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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Windows] usb.core.USBError: [Errno None] libusb0-dll:err [claim_interface] could not claim interface 1, invalid configuration 0","articleBody":"Hello,\r\n\r\nI was working on a test for a device (LadyBug LB5918A Power Sensor) and decided to use python source code that a peer had already written to communicate with it. The code was only tested in a linux environment and being the masochist I am I decided to see if I could at least just identify the device on windows. After using pip to install pyusb \u0026 usbtmc, creating an inf filter with libusb-win32, I ran a brief test script to see if I could just query the device (\"*IDN?\").  Here's the section of the __init__ from the API were the code fails.\r\n```\r\ntry:\r\n\tself.PID = PID\r\n\tself.VID = VID\r\n\t# Initialize USBTMC interface with the LadyBug.\r\n\tself.instr =  usbtmc.Instrument(self.VID, self.PID)\r\n\t#self.instr =  usbtmc.Instrument(0x1A0D, 0x15D8)\r\n\tself.connected = True\r\n\tself.log.debug('Connecting to device with VID: '+str(self.VID)+' and PID: '+str(self.PID))\r\n\tself._send('SYST:PRES DEF')\r\n\tself.log.debug(str(self._request('*IDN?')))\r\n\t#self.clearErr()\r\nexcept Exception as e: \r\n\tself.exceptionHandler(e)\r\n```\r\n\r\nAnd the `__send()` function\r\n```\r\ndef _send(self,msg):\r\n\t\tself.log.debug(str('Writing: '+str(msg)))\r\n\t\tself.instr.write(msg+'\\n')\r\n\t\terr = str(self.instr.ask('SYST:ERR?\\n'))\r\n\t\tif err != '+0,\"No error\"':\r\n\t\t\tself.log.debug(str('LadyBug Error: '+str(err)))\r\n```\r\n\r\nThe error message I get in return is as follows\r\n```\r\n2018-08-03 15:29:08,970 :: ladyBug(DEBUG) :: __init__\r\n2018-08-03 15:29:08,996 :: ladyBug(DEBUG) :: Connecting to device with VID: 6669 and PID: 5592\r\n2018-08-03 15:29:08,997 :: ladyBug(DEBUG) :: Writing: SYST:PRES DEF\r\nTraceback (most recent call last):\r\n  File \"ladyBug-test.py\", line 10, in \u003cmodule\u003e\r\n    lb = ladyBug.meter(0x1a0d,0x15d8,True)\r\n  File \"C:\\Users\\jonathan.bensing\\LadyBug-API\\ladyBug.py\", line 49, in __init__\r\n    self.exceptionHandler(e)\r\n  File \"C:\\Users\\jonathan.bensing\\LadyBug-API\\ladyBug.py\", line 249, in exceptionHandler\r\n    self.instr.open()\r\n  File \"C:\\Python27\\lib\\site-packages\\usbtmc\\usbtmc.py\", line 313, in open\r\n    usb.util.claim_interface(self.device, self.iface)\r\n  File \"C:\\Python27\\lib\\site-packages\\usb\\util.py\", line 205, in claim_interface\r\n    device._ctx.managed_claim_interface(device, interface)\r\n  File \"C:\\Python27\\lib\\site-packages\\usb\\core.py\", line 102, in wrapper\r\n    return f(self, *args, **kwargs)\r\n  File \"C:\\Python27\\lib\\site-packages\\usb\\core.py\", line 167, in managed_claim_interface\r\n    self.backend.claim_interface(self.handle, i)\r\n  File \"C:\\Python27\\lib\\site-packages\\usb\\backend\\libusb0.py\", line 521, in claim_interface\r\n    _check(_lib.usb_claim_interface(dev_handle, intf))\r\n  File \"C:\\Python27\\lib\\site-packages\\usb\\backend\\libusb0.py\", line 431, in _check\r\n    raise USBError(errmsg, ret)\r\nusb.core.USBError: [Errno None] libusb0-dll:err [claim_interface] could not claim interface 1, invalid configuration 0\r\n```\r\n\r\nAfter a lot of googling, I couldn’t seem to find any conclusive reason why this shouldn’t work on windows seeing that I had followed all the steps correctly for both PyUSB and USBTMC setup. I tried just the PyUSB module to identify the device which I was able to do and I then tried to write to the device commands which I know I was most likely doing wrong. I did notice that for most of the examples of PyUSB, the `set_configuration()` function was used a lot to attach to a device. One post that had a similar error said that `set_configuration(1)` should be used and in a rather fluke way I was able to get the device working, so below is the script that cause the device to function properly.\r\n```\r\nmyVendorId =0x1a0d\r\nmyProductId=0x15d8\r\nimport usb.core\r\ndev = usb.core.find(idVendor=myVendorId, idProduct=myProductId)\r\nprint dev\r\ndev.set_configuration(1)\r\nimport ladyBug\r\nlb = ladyBug.meter(0x1a0d,0x15d8,True)\r\nexit()\r\n```\r\nSo I then decided to go through the USBTMC api to see where the issue may be occurring. I believe that the culprit is here in the `open()` function:\r\n```\r\n    def open(self):\r\n        if self.connected:\r\n            return\r\n        # initialize device\r\n        # find first USBTMC interface\r\n        for cfg in self.device:\r\n            for iface in cfg:\r\n                if (self.device.idVendor == 0x1334) or \\\r\n                   (iface.bInterfaceClass == USBTMC_bInterfaceClass and\r\n                    iface.bInterfaceSubClass == USBTMC_bInterfaceSubClass):\r\n                    self.cfg = cfg\r\n                    self.iface = iface\r\n                    break\r\n                else:\r\n                    continue\r\n            break\r\n        if self.iface is None:\r\n            raise UsbtmcException(\"Not a USBTMC device\", 'init')\r\n        try:\r\n            self.old_cfg = self.device.get_active_configuration()\r\n        except usb.core.USBError:\r\n            # ignore exception if configuration is not set\r\n            pass\r\n        if self.old_cfg is not None and self.old_cfg.bConfigurationValue == self.cfg.bConfigurationValue:\r\n            # already set to correct configuration\r\n            # release kernel driver on USBTMC interface\r\n            self._release_kernel_driver(self.iface.bInterfaceNumber)\r\n        else:\r\n            # wrong configuration or configuration not set\r\n            # release all kernel drivers\r\n            if self.old_cfg is not None:\r\n                for iface in self.old_cfg:\r\n                    self._release_kernel_driver(iface.bInterfaceNumber)\r\n            # set proper configuration\r\n            self.device.set_configuration(self.cfg)\r\n\r\n        # claim interface\r\n        usb.util.claim_interface(self.device, self.iface)\r\n``` \r\nAfter stepping through the code manually, the issue is where `self.device.set_configuration(self.cfg)` is never being called. I’m not sure the reasoning behind having the configuration not being set, because it seems that (on windows at least) the old_cfg bConfigurationValue will always be the same as the active cfg bConfigurationValue. And within the usbtmc code I simple moved `self.device.set_configuration(self.cfg)` out of the if statement so that the device will always be set.\r\n```\r\n        if self.old_cfg is not None and self.old_cfg.bConfigurationValue == self.cfg.bConfigurationValue:\r\n            # already set to correct configuration\r\n\r\n            # release kernel driver on USBTMC interface\r\n            self._release_kernel_driver(self.iface.bInterfaceNumber)\r\n        else:\r\n            # wrong configuration or configuration not set\r\n\r\n            # release all kernel drivers\r\n            if self.old_cfg is not None:\r\n                for iface in self.old_cfg:\r\n                    self._release_kernel_driver(iface.bInterfaceNumber)\r\n\r\n        # set proper configuration\r\n        self.device.set_configuration(self.cfg)\r\n```\r\n\r\nI’m not sure if this is intended but I believe that this is how it should be in the code. I hope this helps!\r\n\r\nJon\r\n","author":{"url":"https://github.com/JonBensi","@type":"Person","name":"JonBensi"},"datePublished":"2018-08-06T14:27:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/46/python-usbtmc/issues/46"}