The Windows Driver Model has two separate but equally important aspects. First, the core model describes the standard structure for device drivers. Second, Microsoft provides a series of bus and class drivers for common types of devices.
The core WDM model describes how device drivers are installed and started, and how they should service user requests and interact with hardware. A WDM device driver must fit into the Plug and Play (PnP) system that lets users plug in devices that can be configured in software.
Microsoft provides a series of system drivers that have all the basic functionality needed to service many standard types of device. The first type of system driver supports different types of bus, such as the Universal Serial Bus (USB), IEEE 1394 (FireWire) and Audio port devices. Other class drivers implement standard Windows facilities such as Human Input Devices (HID) and kernel streaming. Finally, the Still Image Architecture (STI) provides a framework for handling still images, scanners, etc.
These system class drivers can make it significantly easier to write some types of device driver. For example, the USB system drivers handle all the low-level communications across this bus. A well defined interface is made available to other drivers. This makes it fairly straightforward to issue requests to the USB bus.
Conclusion
Conclusion
In this chapter, I have tried to give the device driver big picture, showing what components your driver will need and how it fits into the general scheme of things. There are different types of device driver and different ways of implementing the same driver functionality. Some driver components are not compulsory, but it is certainly recommended that you support Plug and Play, Power Management, and Windows Management Instrumentation, if possible.
A crucial part of the Windows Driver Model is the provision of several bus and class drivers. These make it considerably easier to write many types of driver.
In the next chapter, I will look at the crucial background concepts that are needed before device driver development in earnest.