Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Lesson Summary

Lesson Summary

Stream drivers are Windows Embedded CE drivers that implement the stream interface API. The stream interface enables Device Manager to load and manage these drivers, and applications can use standard file system functions to access these drivers and perform I/O operations. To present a stream driver as a file resource accessible through a CreateFile call, the name of the stream driver must follow a special naming convention that distinguishes the device resource from ordinary files. Legacy names (such as COM1:) have a limitation of ten instances per driver because they include only a single-digit instance identification. If you must support more than ten driver instances on a target device, use a device name instead (such as $deviceCOM1).

Because Device Manager can load a single driver multiple times to satisfy the requests from different processes and threads, stream drivers must implement context management. Windows Embedded CE knows two context levels for device drivers, device context and open context, which the operating system passes in each appropriate function call to the driver so that the driver can associate internal resources and allocated memory regions with each caller.

The stream interface consists of 12 functions: XXX_Init, XXX_Open, XXX_Read, XXX_Write, XXX_Seek, XXX_IOControl, XXX_PowerUp, XXX_PowerDown, XXX_PreClose, XXX_Close, XXX_PreDeinit, and XXX_Deinit. Not all functions are mandatory (such as XXX_PreClose and XXX_PreDeinit), yet any functions that the stream device driver implements must be exposed from the driver DLL to Device Manager. To export these functions, you must define them in the .def file of the DLL subproject. You should also adjust the DLL subproject's Sources file to ensure that the driver DLL can make platform-dependent function calls.

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