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 concludes my look at the Human Input Device class driver. It is straightforward to write a user mode application to communicate with a HID device. A Win32 program looks for devices that use the HID device interface. They must then interrogate each device to see if their capabilities are of interest. The program can then read input reports and send output reports.
If need be, you can write a kernel mode HID client. It is best if you use the Plug and Play Notification technique to find any devices that support the HID device interface. Then, you can get the device capabilities and send and receive reports in a broadly similar way to user mode applications.
Both user mode and kernel mode HID clients can make use of the HID parsing routines. These make it much easier to find HID device's capabilities and to generate and understand reports.
