Building the Power-Efficient PC: A Developer's Guide to ACPI Power Management
This book provides developers and integrators with practical knowledge and design techniques for building PCs that address the increasing demand for energy conservation.
TABLE OF CONTENTS Building the Power-Efficient PC: A Developer's Guide to ACPI Power Management
Chapter 11: Drivers
Device drivers implement the software layer between the operating system and devices in the system. Although most device drivers manage physical components like hard drives, displays, or network interfaces, virtual device drivers manage system functions distributed across multiple components. Power management device drivers are virtual device drivers, controlling the interface to ACPI.
Device drivers and ACPI power management drivers, along with intelligence in the operating system, work together to direct and control the power state of all devices in a power-managed system.
Device Power
Because peripheral devices consume a significant portion of a system s total power budget, efficient device power management is crucial for reducing PC power consumption. Only the processor, which itself is well-managed in most implementations, consumes more power than peripheral devices in a typical desktop PC. With increasingly device-laden systems and powered peripheral buses like USB and IEEE 1394, peripheral device power requirements may soon eclipse those of all other components of the system.
The latency to switch the processor into and out of its idle power state is far less than that for peripheral devices, but most system devices are usually idle in both desktop and mobile systems. Only a small set of devices is typically required for common applications like word processing and web browsing. Moreover, the devices used by those applications require processor time infrequently. Over a 24-hour period, computer systems spend most of the time completely unused, with no device activity and with the monitor veiled behind a screen saver. Even machines...
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