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Chapter 8 BIOS ROM
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
8-14
8.5 POWER MANAGEMENT FUNCTIONS
The BIOS provides three types of power management support: independent PM support; ACPI
support, and APM support. These power management interfaces share a common goal of
reducing energy consumption during periods of system inactivity. The following table compares
and describes the different system states identified by the various power management interfaces.
Global
State
Sleep
State System Condition
Power
Consumption
OS Restart
Required
G0 -- Fully on. OS and application software is
running, all devices are active, responsive,
and maintaining context.
Maximum No
G1 S1
S2/S3
S4
On, with CPU executing and data held in
memory, but peripheral devices (display
output, some I/O) may be disabled/low power.
On, but CPU not executing and cache context
lost. Memory is maintained. Display and I/O
devices disabled or under low power.
Off. CPU and most other devices powered off.
No data held in RAM, but memory image from
lower state has been saved to disk for recall
upon wake up.
Low
Low
Low
No
No
Yes
G2 S5 Soft Off. OS has completed shutdown. Some
devices may be powered to allow for “wake
up” to occur resulting in a full boot sequence.
Minimum Yes
G3 -- Mechanical off. Power to unit has been
switched off (or unit has been unplugged).
Only internal RTC battery power is being
consumed. Unit may be
disassembled/serviced safely.
None Yes
8.5.1 INDEPENDENT PM SUPPORT
The BIOS ROM can provide power management of the system independently from any software
(OS or application) that is running on the system. In this mode the BIOS uses a timer to
determine when to switch the system to a different power state. State switching is not reported to
the OS and occurs as follows:
On
– The computer is running normally and is drawing full power.
Standby
– The computer is in a low power state. In this state the processor and chipset are still
running and the VSYNC signal to the monitor is turned off. Returning to the On state requires
very little time and will be initiated by any of the following actions:
a.
key stroke
b.
mouse movement
Off
– The computer is not running and drawing practically no power at all.