Overview

Mobile PCs typically laptops and handhelds differ from desktop systems not in the fundamental power management technologies, but in degree. Mobile systems have incorporated power management technologies sooner and more aggressively than desktops in the search for longer battery life. You ll learn in this chapter that, using ACPI, there are several key differences for mobile platform power management:

• The target power consumption is less for each subsystem.

• There are tighter limits on cooling, which limits power consumption.

• Lowering the processor frequency and voltage can reduce power consumption. Throttling the practice of modulating the processor STPCLK pin can help thermal management, but generally doesn t increase battery life.

• Processor states used less frequently on desktops, including C2 and C3, are standard for mobile.

• The keyboard controller has added features in mobile systems, making it an embedded controller for thermal management, battery control, and other essential functions.

• Battery-driven power supplies can be exhausted in mobile systems, leading to implementation requirements for sleep states not found in desktop systems.

We ll cover each of these differences in the following sections.

Mobile Implementation Targets

Operating battery life and limited cooling are the drivers for all power management design decisions in mobile systems. Power you don t dissipate stays in the battery, and doesn t have to be exhausted to keep temperatures low.