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 introduced the WdmIo and PHDIo drivers. It has described the facilities that they make available to Win32 applications. WdmIo has its resources specified in its INF file. The resources are given to PHDIo in the Win32 CreateFile call. The WdmIoTest example user mode application uses WdmIo to drive a parallel port printer and output a short message. The similar PHDIoTest application does similar tests using the PHDIo driver.
The next chapters look at the construction of these drivers, how they queue IRPs to serialize hardware access and they perform interrupt driven I/O.
