libusb-win32 | libusb-win32 Sourceforge subversion repo export | Code Editor library

msg = '*IDN?'

This is not a complete SCPI command: It is missing the newline \n character at the end.

That is also why the device was not able to send an answer via USB.

Looks like you're using a Python libusb wrapper. This will only enumerate USB devices which have actually been associated with the libusb driver. Every device is associated with a driver, and most will have class drivers (eg HID, UVC, MSC, etc) provided by the OS, so you need to use a different API to access them. You can enumerate all devices in a generic fashion by using the native SetupAPI and WinUSB on Windows, if that's what you really want. But this wrapper will only enumerate devices that specifically use the libusb driver. Since your code doesn't show any, you probably just don't have a device that uses libusb.

You can use the Zadig tool to remap drivers to different devices. But beware of doing this as you can easily break things if you happen to choose an unsupported configuration. It's normally used when you have a custom or 3rd party device.

Although I still cannot communicate with the device on the Raspberry Pi, the Error 5 problem is resolved by explicitly selecting a suitable alternate setting with proper endpoints, e.g.

The Keysight support helped me out: I had to install the Keysight drivers (connection expert) and the pyvisa and pyvisa-py module. It is now working!

Answering my own question here. So, it turns out, the problem was with python-escpos library. I had to remove the following from the printer.py (python module of that library):

The usb_find_devices() documentation in the libusb 0.1 API says:

Returns the number of changes since the previous call to this function (total of new device and devices removed).

So, it does not return the number of available devices, like you are expecting. If you need that value, enumerate the bus list counting the devices yourself. Otherwise, just ignore the count and move on to your bus printing loop, it will run across any connected devices.

That being said, there is a newer libusb 1.0 API, but its documentation does not mention usb_find_devices() at all. usb_find_devices() appears to have been replaced with a new usb_get_devices_list() function:

Returns a list of USB devices currently attached to the system.

This is your entry point into finding a USB device to operate.

You really should be using the newer 1.0 API, per the libusb website:

There are several libusb-0.1 API implementations:

• libusb-0.1 is the very first libusb implementation.
• libusb-compat-0.1 is a compatibility library which provides the libusb-0.1 API by using the libusb-1.0 API.
• libusb-win32 is a Windows-only implementation of the libusb-0.1 API. The libusb-win32 project has also created the open source libusb0.sys Windows kernel driver, which exposes a userspace API that allows USB devices to be accessed outside of the Windows kernel.

...

Because the 0.1 and 1.0 APIs use different prefixes they are compatible with each other. It is common that both are installed in parallel on a system. We strongly recommend using libusb-1.0 together with libusb-compat-0.1 instead of the ancient libusb-0.1 code, so that programs which use both the 0.1 API and the 1.0 API in different parts of the program, or in different libraries used by the program, will all use libusb-1.0 for the actual device access. This is important to avoid potential conflicts between libusb-1.0 and libusb-0.1 being used in the same process.

... libusb-1.0 is recommended for all new development. Developers are encouraged to port existing applications which use libusb-0.1 to use the new API.

...

libusb-0.1 (legacy API)

...

• Note that libusb-win32 is a separate project which still sees active development. The next generation libusb-win32 kernel driver (libusbk.sys) is based on KMDF. The ​libusbk library will support the existing libusb-win32 API, libusb-1.0 API and WinUSB-like API. libusb-win32 users who are fine with the libusb-win32 API are recommended to keep using it since it will be supported by the libusb-win32 project. libusb-win32 users who are interested in libusb-1.0 will also be supported once the libusbk backend is integrated. Future enhancement of the libusb-1.0 API (say libusb-1.1) may be required to be more suitable for Windows users.

It's most likely in the package LibUsbDotNet. If you are using Visual Studio, open up Tools > NuGet Package Manager > Manage NuGet Packages for Solution..., go to Browse and paste it into the search bar. Add it to your project and now it should be good to go.