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
This chapter has looked in detail at a practical Plug and Play function driver implementation for Wdm2 devices. The Wdm2 driver now handles all its PnP operations safely. The Wdm2Test Win32 test program checked that the Wdm2 driver could not be removed or replaced while its devices had open handles.
We also looked at how Plug and Play Notification can inform Win32 and device drivers of device change events. The Wdm2Notify Win32 test program displays any device change events for the Wdm2 device interface. Finally, bus drivers were briefly described.
The next chapter completes the discussion of the Wdm2 driver by describing its Power Management features.
