Summary

• For certain types of devices, including USB devices, the I/O Kit makes it possible to forgo a kernel driver and implement the driver completely in user space. For the end user, this provides a much better experience.
• Not all USB devices are suitable for a user-space driver. A device that needs to be used by the system itself, such as a system-wide audio device or a USB storage device, must be implemented in the kernel.
• The I/O Kit provides a user-space library known as IOUSBLib that an application uses to interact with a USB device. The IOUSBLib provides a user- space equivalent to the IOUSBDevice and IOUSBInterface kernel classes, known as IOUSBDeviceInterface and IOUSBInterfaceInterface, respectively.
• An application can watch for the arrival and removal of the USB devices it supports by creating a matching dictionary and installing a notification callback, as described in Chapter 5. Once an application has been notified that a USB device or a USB interface it is interested in has been attached to the computer, it can instantiate an IOUSBDeviceInterface or IOUSBInterfaceInterface object to provide access to the USB hardware.
• The IOUSBLib provides full support for the functionality of a USB device to a user-space driver. All endpoint types are supported in user space, including control, bulk, interrupt, and isochronous transfers.
• An application can perform either synchronous or asynchronous operations with IOUSBLib. A callback is used to notify the application of the completion of an asynchronous request.