Chapter 10. Power Management

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[oR]

CHAPTER OBJECTIVES

Hot Plug Devices
OnNow Initiative
Wake Requests
Power Management Issues
Summary

The WDM model is ideal for enumerating and arbitrating discovered hardware. Additionally, the model supports the frugal management of power to those devices.

Devices that consume power only when used are hardly a new concept. After all, household appliances normally remain off until used. Yet within legacy computers, every device consumes power even during significant idle periods. The fact that a device might be burning just a few watts or less encourages the thought that the waste is unworthy of concern.

The need to manage power to installed devices is obvious in mobile and portable environments where the source of energy is limited. Even in desktop and server environments, however, the reduction of unnecessary power expenditure lowers heat production, increases component reliability, and lowers electric consumption and cost.

This chapter starts by describing the goals of and problems associated with power management. Then the mechanics of power management with a device driver is presented. This involves gracefully powering down a device through various levels of power consumption and reversing the process when new device requests arrive.

Finally, an example driver with power management handling incorporated is presented.

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