The USB device filesystem is a dynamically generated filesystem that complements the normal device node system, and can be used to write user space device drivers. Writing of user space device drivers is covered in the programmer's section of this guide. In addition to the device nodes, there are two files that are also generated - the drivers and devices files. This is most useful when testing module installation, and checking for USB support in an unknown kernel. This is very useful when trying to figure out if the device is correctly enumerated.
Bus indicates which bus the device is on.
Lev indicates the level of the device, starting at level 00 for the root hub, level 01 for any device attached to the root hub, level 02 for devices attached to hubs at level 01, and so on. Port is the port on the parent device, starting at 00 for the first port on each device. Cnt indicates what number device this is, at this level, based on the enumeration order within that level of the topology, starting at 01 for the first device. This is unique per bus. MxCh indicates how many devices can be connected to this device, and is 00 for anything except a hub.