Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Chapter Review

Windows Embedded CE 6.0 is extraordinarily modular in its design and supports ARM-, MIPS-, SH4-, and x86-based boards in a multitude of hardware configurations. The CE kernel contains the core OS code and the platform-specific code resides in the OAL and in device drivers. In fact, device drivers are the largest part of the BSP for an OS design. Rather than accessing the hardware directly, the operating system loads the corresponding device drivers, and then uses the functions and I/O services that these drivers provide.

Windows Embedded CE device drivers are DLLs that adhere to a well-known API so that the operating system can load them. Native CE drivers interface with GWES while stream drivers interface with Device Manager. Stream drivers implement the stream interface API so that their resources can be exposed as special file system resources. Applications can use the standard file system APIs to interact with these drivers. The stream interface API also includes support for IOCTL handlers, which come in handy if you want to integrate a driver with Power Manager. For example, Power Manager calls XXX_IOControl with an IOControl code of IOCTL_POWER_SET passing in the requested device power state.

Native and stream drivers can feature a monolithic or layered design. The layered design splits the device driver logic in an MDD and a PDD part, which helps to increase the reusability of the code. The layered design also facilitates driver updates. Windows Embedded CE also features a flexible interrupt-handling architecture based on ISRs and ISTs. The ISR's main task is to identify the interrupt source and notify the kernel with a SYNTINR value about the IST to run. The IST performs the majority of the processing, such as time-consuming buffer copying processes.

In general, you have two options to load a driver under Windows Embedded CE 6.0. You can add the driver's registry settings to the BuiltIn registry key to start the driver automatically during the boot process or you load the driver automatically in a call to ActivateDeviceEx. Depending on the driver's registry entries, you can run a driver in kernel mode or user mode. Windows Embedded CE 6.0 includes a user-mode driver host process and a Reflector service that enables most kernel-mode drivers to run in user mode without code modifications. Because device drivers run in different process spaces than applications on Windows Embedded CE 6.0, you must marshal the data in either a mapping of physical memory sections or copying process to facilitate communication. It is imperative to validate and marshal embedded pointers by calling CeOpenCallerBuffer and CeAllocAsynchronousBuffer and properly handling asynchronous buffer access so that a user application cannot exploit a kernel-mode driver to take over the system.

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