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Chapter 8 BIOS ROM
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
8-18
8.6 POWER MANAGEMENT SUPPORT
The Compaq Deskpro 2000 system includes Advanced Power Management (APM) BIOS support
that provides, if so configured, for the automatic shutdown of certain areas within a system after
a specified time of inactivity has elapsed. When activity is detected, APM brings the system back
up to full power to provide complete user support.
For maximum energy-conservation benefit, APM functionality should be implemented using the
following three layers:
♦ BIOS layer (APM BIOS (ver. 1.2, 1.1, 1.0))
♦ Operating system (OS) layer (APM driver)
♦ Application layer (APM-aware application or device driver)
The BIOS layer informs the OS or driver when hardware events occur (or don’t occur) so that a
transition to another power state should take place. The process starts with the OS or driver
making a connection with the BIOS through an APM BIOS call. In a DOS environment
POWER.EXE makes a Real mode connection. In Windows 3.1 and in Windows 95, a 32-bit
connection is made. Currently Windows NT does not make an APM connection.
With power management enabled, inactivity timers are monitored. When an inactivity timer
times out, an SMI is sent to the microprocessor to invoke the SMI handler. The SMI handler
works with the APM driver and APM BIOS to take appropriate action based on which inactivity
timer timed out.
Two I/O ports are used for APM communication with the SMI handler:
Port Address
Name
0B2h APM Control
0B3h APM Status
Three power states are defined under power management:
On
- The computer is running, all subsystems are on and drawing full power. Any activity in the
following subsystems will reset the activity timer, which has a default setting of 15 minutes
before Standby entered:
a. Keyboard
b. Mouse
c. Serial port
d. Diskette drive
e. Hard drive