In this topic you'll use the USB User-Mode Driver template provided with Microsoft Visual Studio 2012 to write a user-mode driver framework (UMDF)-based client driver. After building and installing the client driver, you'll view the client driver in Device Manager and view the driver output in a debugger.
UMDF (referred to as the framework in this topic) is based on the component object model (COM). Every framework object must implement IUnknown and its methods, QueryInterface, AddRef, and Release, by default. The AddRef and Release methods manage the object's lifetime, so the client driver does not need to maintain the reference count. The QueryInterface method enables the client driver to get interface pointers to other framework objects in the Windows Driver Frameworks (WDF) object model. Framework objects perform complicated driver tasks and interact with Windows. Certain framework objects expose interfaces that enable a client driver to interact with the framework.
A UMDF-based client driver is implemented as an in-process COM server (DLL), and C++ is the preferred language for writing a client driver for a USB device. Typically, the client driver implements several interfaces exposed by the framework. This topic refers to a client driver-defined class that implements framework interfaces as a callback class. After these classes are instantiated, the resulting callback objects are partnered with particular framework objects. This partnership gives the client driver the opportunity to respond to device or system-related events that are reported by the framework. Whenever Windows notifies the framework about certain events, the framework invokes the client driver's callback, if one is available. Otherwise the framework proceeds with the default processing of the event. The template code defines driver, device, and queue callback lasses.
For an explanation about the source code generated by the template, see Understanding the UMDF template code for USB client driver.
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