Highlights

This chapter looks at the design of the Plug and Play (PnP) system and how PnP drivers fit into a device stack. A device stack is the means by which several layers of drivers can work together to process user requests. The next chapter looks at how to implement Plug and Play in detail, and describes the Wdm2 example. As well as PnP, Wdm2 supports Power Management, as described in Chapter 10.

Plug and Play in a different form is available in Windows 95 for virtual device drivers (VxDs). NT 4 does not support Plug and Play. Therefore, the Windows 98 and Windows 2000 support for Plug and Play in the Windows Driver Model is new for both environments. If you have any old NT 4 kernel mode device drivers, Microsoft recommends that you update them to support Plug and Play and Power Management. However, supporting Plug and Play requires a major change to driver code, so you will have to judge whether it is worthwhile.

Although Plug and Play initially looks complicated, it is possible to use the code the Pnp.cpp module described in the next chapter for most drivers. Careful use of the LockDevice and UnlockDevice routines is all that is needed elsewhere.

Design Overview

From a user's point of view, Plug and Play is straightforward. You just plug in some new equipment and Windows finds the device and prompts you for the correct drivers. Then you play with your new device.

The main...