Technical Reference Guide

7.7POWER MANAGEMENT FUNCTIONS

The BIOS ROM provides three types of power management support: independent PM support; APM support, and ACPI support.

7.7.1 INDEPENDENT PM SUPPORT

The BIOS can provide power management (PM) of the system independently from an operating system that doesn’t support APM (including DOS, Unix, NT & older versions of OS/2). In the Independent PM environment the BIOS and hardware timers determine when to switch the system to a different power state. State switching is not reported to the OS.

7.7.1.1 Staying Awake In Independent PM

There are two "Time-out to Standy" timers used in independent PM: the System Timer and the IDE Hard Drive Timer.

System Timer

In POST, the BIOS enables a timer in the ICH that generates an SMI once per minute. When the BIOS detects the SMI it checks status bits in the ICH for device activity. If any of the device activity status bits are set at the time of the 1-minute SMI, BIOS resets the time-out minute countdown. The system timer can be configured through the Setup utility for counting down 0, 5, 10, 15, 20, 30, 40, 50, 60, 120, 180, or 240 minutes. The following devices are checked for activity:

Keyboard

Mouse

Serial port(s)

Parallel port

IDE primary controller

NOTE: The secondary controller is NOT included. This is done to support auto- sense of a CD-ROM insertion (auto-run) in case Windows or NT is running. Note also that SCSI drive management is the responsibility of the SCSI driver. Any IDE hard drive access resets the hard drive timer.

IDE Hard Drive Timer

During POST, an inactivity timer each IDE hard drive is set to control hard drive spin down. Although this activity is independent of the system timer, the system will not go to sleep until the primary IDE controller has been inactive for the system time-out time. The hard drive timer can be configured through the Setup utility for being disabled or counting down 10, 15, 20, 30, 60, 120, 180, or 240 minutes, after which time the hard drive will spin down.

Compaq Evo and Workstation Personal Computers7-17

Featuring the Intel Pentium 4 Processor

Second Edition - January 2003

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Compaq W4000 manual Power Management Functions, Independent PM Support, Staying Awake In Independent PM, System Timer