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.
Under 3. Real-time processing can be achieved by raising a given IST's priority, but again, the impact of doing so must be reviewed against the other ISTs in the system. It is a good practice to store a driver's priority in the registry where it can easily be modified, as opposed to hard-coding it in the driver.
This naturally requires the driver to load the priority value from the registry and adjusts the IST's priority accordingly once created.
An IST can also set its quantum the time it executes before the scheduler kicks in to a value other than the default which is set in the OAL. In particular, an IST can set its quantum to 0, which means run to completion.
However, whatever the quantum value is, interrupts are still processed. Should a higher priority thread become ready to run as the result of processing an interrupt, this thread will preempt the current thread. Therefore, run-to-completion is useful if the driver doesn't want to be interrupted by another thread of the same priority in a multi-threaded driver for instance.
Running to completion has little impact on the overall system performance, since higher-priority threads can still preempt as needed. There is no doubt that developing drivers for Windows CE 3. However, it is important to note that custom driver development requires substantial work, ranging from a few weeks to a few months. Engineers new to CE typically require three to six months to go through the steep learning curve, although training class will probably reduce the period of time.
No matter what approach you take, it is important to allocate ample resources and time for Windows CE device driver development. Since , he's been involved in the development of Windows CE devices, from platform adaptation to application development. Contact him at. You must Sign in or Register to post a comment. This site uses Akismet to reduce spam. Learn how your comment data is processed.
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Stream interface drivers Stream interface drivers all share a common interface. 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.
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.
Tools Microsoft provides a driver development tool called Platform Builder. Real-time considerations Windows CE v.
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The changes finally saw the delivery of Pocket Office onto the QVGA form factor The primary goal for the new release was to move the appeal of Microsoft's portable device offerings beyond the general PDA user, and into new fields such as knowledge workers and mobile workers.
The Pocket PC program ran under the development code name Rapier, a type of sword. While Microsoft were revolutionising their work on the Handheld PC's younger sister. The new Platform Builder provided the functionality of the Windows CE 3 Core, as well as incorporating the various new technologies that had emerged during and since the CE 2. However the remaining updates were far from as illustrious as that of the Pocket PC.
However HPC had failed to address many of the key issues that the End User had with the applications that were onboard. The release attempted to rebrand the applications into line with the Office scheme, however the fact that it was nothing more than a patched build quickly shone through.
Despite this, the Windows CE 3. A clear shift in Microsoft's development policy of Windows CE was starting to emerge. Microsoft central marketing almost exclusively Pocket PC orientated, and internal development inside Microsoft Mobile for applications and enhancements began to trail off by mid This is a Windows CE 4 wide omission. It is important to reminder that Windows CE development within Microsoft is not the same as Mobile Device development. They are two separate departments.
By the beginning of there was no longer any department, or individual charged with work on the Handheld PC in any Microsoft subsidiary, anywhere in the world. Conversely, all Platform construction tools used codenames of tools used to cut down trees.
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