USB support in the I/O Kit is provided by the
IOUSBFamily, which is a dynamically loadable KEXT, identified by the bundle identifier
com.apple.iokit.IOUSBFamily. The USB family provides the central core of USB handling in the kernel and contains drivers for the host controllers, as well as abstraction classes for representing USB devices, interfaces, and pipes. The class hierarchy of the USB Family is shown in Figure 8-4.
Most of these classes are irrelevant if you only want to implement a driver for a USB device. The main classes used for USB driver development are shown in gray, ...