Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Lesson Summary

Lesson Summary

Windows Embedded CE can load drivers into kernel space or user space. Drivers running in kernel space have access to system APIs and kernel memory and can affect the stability of the system if failures occur. However, properly implemented kernel- mode drivers exhibit better performance than user-mode drivers, due to reduced context switching between kernel and user mode. On the other hand, the advantage of user-mode drivers is that failures primarily affect the current user-mode process. User-mode drivers are also less privileged, which can be an important aspect in respect to non-trusted drivers from third-party vendors.

To integrate a driver running in user mode with Device Manager running in kernel mode, Device Manager uses a Reflector service that loads the driver in a user-mode driver host process and forwards the stream function calls and return values between the driver and Device Manager. In this way, applications can continue to use familiar file system APIs to access the driver, and the driver does not need code changes regarding the stream interface API to remain compatible with Device Manager. By default, user-mode drivers run in separate host processes, but you can also configure host process groups and associate drivers with these groups by adding a corresponding UserProcGroup registry entry to a driver's registry subkey. Driver subkeys can reside in any registry location, yet if you want to load the drivers at boot time automatically, you must place the subkeys into Device Manager's RootKey, which by default is HKEY_LOCAL_MACHINEDriversBuiltIn. Drivers that have their subkeys in different locations can be loaded on demand by calling the ActivateDeviceEx function.

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