Writing Windows WDM Device Drivers
A nuts-and-bolts reference highlighting the Windows Driver Model (WDM).
TABLE OF CONTENTS Writing Windows WDM Device Drivers
Chapter 10: Power Management
This chapter investigates how to support Power Management in WDM device drivers. NT style drivers in Windows 2000 and Windows 98 can also support Power Management. A device can change its power usage in response to system power state changes, and can reduce its own power usage when it has been idle for a while. A sleeping device can wake the system up, such as when a modem receives an incoming call.
The Power Management aspects of the example Wdm2 driver are explained. The Win32 application Wdm2Power can be used to test Power Management facilities.
The Power Picture
Device drivers play a crucial role in helping Windows make the most of the available power resources. This means reducing power consumption in low power situations, such as when running on batteries. Drivers that support power management can also help to minimize startup and shutdown times. Finally, turning off some devices reduces system noise and turning off the display can save a monitor screen.
Most desk-based computers only run on AC power. However, they may have one or more Uninterruptible Power Supplies (UPS) with batteries to provide power in case of emergencies when main power is lost. Most portable computers are able to run off both battery (DC) and AC power.
The system should detect when the computer is running from battery power and reduce power consumption wherever possible. If not in use, it should suspend itself into a standby sleep mode. When running from batteries, the system...
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