How to sniff a USB port under Windows?
Since people don't seem to realize it, Wireshark does monitor USB traffic and has a parser for it; but the catch is it only works under Linux. Wireshark on Windows will not do this.
It may be possible to plug the USB device you want to monitor, along with a Linux machine (with Wireshark running) and your Windows machine and just use the USB device under Windows.
Problem with the above? I don't know how the Linux machine or the Windows machine will detect each other.
After five years waiting, now it's possible to sniff usb packets on windows
See http://desowin.org/usbpcap/tour.html for a quick tour. It works pretty well
Busdog, an open source project hosted on github, has worked well for me. It has a driver it installs to allow it to monitor USB communications. The config window allows you to reinstall or remove the device at any time.
You can select the USB device you want from an enumerated list. A nice feature is to have it automatically trace a new device that is plugged in:
Data communications to and from an SWR analyzer I was reverse engineering were captured flawlessly:
