Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Native and Stream Drivers

Native and Stream Drivers

A Windows Embedded CE device driver is a DLL that exposes the standard DllMain function as the entry point, so that a parent process can load the driver by calling LoadLibrary or LoadDriver. Drivers loaded by means of LoadLibrary can be paged out, but the operating system does not page out drivers loaded through LoadDriver.

While all drivers expose the DllMain entry point, Windows Embedded CE supports two different types of drivers: native drivers and stream drivers. Native CE drivers typically support input and output peripherals, such as display drivers, keyboard drivers, and touchscreen drivers. The Graphics, Windowing, and Events Subsystem (GWES) loads and manages these drivers directly. Native drivers implement specific functions according to their purpose, which GWES can determine by calling the GetProcAddress API. GetProcAddress returns a pointer to the desired function or NULL if the driver does not support the function.

Stream drivers, on the other hand, expose a well-known set of functions that enable Device Manager to load and manage these drivers. For Device Manager to interact with a stream driver, the driver must implement the Init, Deinit, Open, Close, Read, Write, Seek, and IOControl functions. In many stream drivers, the Read, Write, and Seek functions provide access to the stream content, yet not all peripherals are stream devices. If the device has special requirements beyond Read, Write, and Seek, you can use the IOControl function to implement the required functionality. The IOControl function is a universal function that can accommodate any special needs of a stream device driver. For example, you can extend a driver's functionality by passing a custom IOCTL command code and input and output buffers.

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