Apm Support - Compaq Deskpro EP 6233 Technical Reference Manual

Chapter 7 BIOS ROM
7.6.3

APM SUPPORT

Advanced Power Management (APM) BIOS support provides interaction between the BIOS
ROM and the operating system (OS). The BIOS advises the OS when a power state transition
should occur. The OS then notifies the appropriate driver(s) and reports back to the BIOS.
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 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:
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
7-22 Compaq Deskpro EP Series of Personal Computers
Port Address
0B2h
0B3h
First Edition - April 1998
Name
APM Control
APM Status