Stream drivers can be loaded at various points in time. For built-in devices, such as an audio card, stream drivers are loaded at boot time via entries in the Registry. For detectable devices a serial port implemented on a PC card for instance , the related driver is loaded at detection time, again using entries in the registry. Finally, applications can specifically request a driver to be loaded at run-time, by calling LoadDriver , for instance.
Stream drivers are loaded, managed, and unloaded by the device manager module. Stream interface drivers typically rely on native drivers to perform their duties. For instance, a bar code reader will rely on the serial port driver to physically access the device. In this instance, the bar code reader is called a client driver, and would use the Win32 file API to access the serial driver, the same way an application would. Client drivers are useful because they encapsulate implementation details, such as processing data into a bitmap image, that applications do not have to be concerned about.
The full USB host-side specification is supported on CE, including the various data transfer methods-control, isochronous, interrupt-driven, and bulk. USB drivers can be implemented using three approaches. First, a USB driver can be implemented as a standard stream-interface driver, allowing applications to use the file API to access the device.
NDIS drivers. Only a subset of the original specification, NDIS 4. As a result, miniport drivers are supported, but monolithic and full drivers are not. Fortunately, miniport drivers are largely source-compatible with those on NT. Microsoft provides various NDIS driver samples, and recommends porting an existing NT driver, if one is available, rather than creating one from scratch. Device driver implementation.
Adapting Windows CE to a specific platform is mostly a matter of developing the drivers for the particular devices the board features. The other aspects are to configure, build, and test the Windows CE image itself. Driver development, as I will explain, consists of implementing interrupt handlers driectly in the kernel and the code that access the devices the drivers themselves.
Interrupts are processed in unique fashion in Windows CE, as shown in Figure 1. The kernel's event handler is the first to catch a raised interrupt. The interrupt, as well as lower priority interrupts, are disabled, but all other interrupts of higher priority remain enabled provided the underlying architecture supports nesting interrupts based on their priorities.
The related interrupt service routine ISR is then called. The sole purpose of the ISR is to return a logical identifier to the interrupt service handler ISH in the kernel, but it can implement more functionality if performance is an issue.
Since Windows CE 3. For instance, ISRs that implement critical code that can't be preempted must temporarily disable all interrupts. However, this should be done only to execute a few instructions, since keeping higher-priority interrupts disabled may interfere with the real-time nature of the system more about this later.
The kernel uses the returned logical identifier to unblock the related interrupt service thread IST. The IST resides in the driver and implements the core driver's functionality interrupt processing by accessing the hardware as required. Once the interrupt is processed, the IST signals the end of interrupt and the kernel re-enables the interrupt. Developers can assign one handler per interrupt or one handler for multiple interrupts.
Listing 2 shows parts of the serial communication interrupt handling on an x86 platform. The code is adapted from Platform Builder 3. Listing 3 shows parts of the IST of a serial communication driver for an x86 platform.
This thread waits for the event object to be set by the kernel when the ISR returns the related interrupt identifier , then handles the interrupt. Once the interrupt is processed, the thread calls Interrupt-Done to signal the interrupt processing completion to the kernel. Driver architecture.
As mentioned above, built-in devices can be controlled by native drivers, which are linked with the GWES, and stream interface drivers, which areloaded by the device manager. Drivers linked with the GWES must adhere to a predefined interface called the device driver interface DDI , whereas stream interface drivers are required to implement the standard stream functions. Drivers for built-in devices can have a layered or monolithic architecture, as illustrated in Figure 2.
A layered driver relies on a piece of code that can be reused across platforms to simplify and shorten the development time. This code, provided by Microsoft, is called the module device driver MDD and implements the core functionality of the driver. It doesn't access the hardware directly, but relies on another piece of code, which is hardware-dependent, called the platform-dependent driver PDD. When porting a layered driver from one platform to another, only the PDD has to be rewritten, not the entire driver.
If performance is an issue, one might prefer to develop a given driver as a monolithic piece of code, as opposed to a layered one. The development time is increased, and the code cannot easily be ported to another platform, but a tighter integration-which is what a monolithic driver provides-might be the only approach to meet certain performance requirements. Whichever architecture is retained, the driver must always conform to the DDI for the device it controls.
Most drivers for built-in devices follow a layered architecture because Microsoft provides layered samples for them. Nonetheless, an OEM can re-implement those drivers to better fit its devices.
The only drawbacks are that the modified MDD might not be as portable as the original of course, this might not be an issue , and changes might be required in the PDD. Microsoft provides a driver development tool called Platform Builder. Actually, Platform Builder allows building, downloading, and debugging complete Windows CE images including device drivers for various processors.
It integrates an editor, cross-compilers for all supported processors, a linker, an integrated debugger, an image loader, and a flock of additional tools. New to Platform Builder v. It also includes the device driver test kit DDTK to test the native drivers extensively. Real-time considerations. Windows CE v. Device drivers are not immune to those changes and can, in fact, diminish real-time performance if not properly implemented.
As mentioned earlier, nested interrupts are supported based on their priorities. Note that some architectures do not support nesting interrupts on their priorities x86 is one , so this concept does not always apply. If it does, ISRs must be written accordingly. For instance, critical sections might require turning off all interrupts.
This is even more true if, for performance consideration, the interrupt is directly processed in the ISR instead of the IST. In such a case, turning off interrupts directly impacts the systems' interrupt latency, and may degrade the overall system performance if not carefully fine-tuned.
Interrupt service threads are subject to premption by the scheduler based on their priority, a situation that may not be acceptable in some cases. Download Download. This is a downloadable archive of the Windows CE 3. Quick Details Version:. File Name:. Date Published:. File Size:. System Requirements Supported Operating Systems:. Instructions The download is a compressed folder file. To start the download, click Download. VirtualDJ Avast Free Security. WhatsApp Messenger. Talking Tom Cat.
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