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Power Management

Power consumption in a GX1 processor based system is

managed with the use of both of hardware and software.

The complete hardware solution is provided for only when

the GX1 processor is combined with a Geode I/O compan-

ion such as the CS5530.

The GX1 processor power consumption is managed prima-

rily through a sophisticated clock stop management tech-

nology. The GX1 processor also provides the hardware

enablers from which the complete power management

solution depends on.

Typically the three greatest power consumers in a battery

powered device are the display, the hard drive (if it has one)

and the CPU. Managing power for the first two is relatively

straightforward and is discussed in the CS5530 I/O com-

panion data book. Managing CPU power is more difficult

since effective use of the clock stop technology requires

effective detection of inactivity, both at a system level and

at acodeprocessinglevel.

Basically two methods are supported to manage power

during periods of inactivity. The first method, called activity

based power management allows the hardware in the

Geode I/O companion to monitor activity to certain devices

in the system and if a period of inactivity occurs take some

form of power conservation action. This method does not

require OS support because this support is handled by

SMM software. Simple monitoring of external activity is

imperfect as well as inefficient. The second method, called

passive power management, requires the OS to take the

active role in managing power. National supports two appli-

cation programming interfaces (APIs) to enable power

management by the OS: Advanced Power Management

(APM) and Advanced Configuration and Power Interface

(ACPI). These two methods can be used independent of

one another or they can be used together. The extent to

which these resources are employed depends on the appli-

cation and the discretion of the system designer.

The GX1 processor and Geode I/O companion chips con-

tain advanced power management features for reducing

the power consumption of the processor in the system.

5.1

POWER MANAGEMENT FEATURES

The GX1 processor based system supports the following

power management features:

• GX1 processor hardware

— System Management Mode (SMM)

— Suspend-on-Halt

— CPU Suspend

— 3 Volt Suspend

— GX1 Processor Serial Bus

• Geode I/O companion hardware:

— I/O activity monitoring

– SMI generation

— CPU Suspend control

– Suspend Modulation

– 3 Volt Suspend

— ACPI hardware

• Software:

— API for APM aware OS

— API for ACPI aware OS

— PM VSA for not PM aware OS’s

Geode I/O companion power management support is dis-

cussed in this specification only when necessary to better

explain the GX1 processor’s power management features.

Software support of power management is discussed in

this specification only when necessary to better explain the

GX1 processor’s power management features.

5.1.1

System Management Mode

The GX1 processor has an operation mode called System

Management Mode. This mode is generally entered when

the SMI# pin goes active. SMM is explained in Section 3.7

“System Management Mode” on page 83. If active power

management is desired, then the Geode I/O companion is

programmed at boot time to activate SMM through the

SMI# pin due to specific I/O inactivity.

SMM is also used in the passive power management

method, however, it is limited to supporting specific API

calls such as entering sleep modes.

5.1.2

Suspend-on-Halt

Suspend-on-Halt is the most effective power reducing fea-

ture of the GX1 processor with the system active. This fea-

ture allows the system to reduce power when the system’s

OS becomes idle without producing any delay when the

system’s OS becomes active.

When entered, Suspend-on-Halt stops the clock to the pro-

cessor core while the intergrated functions (graphics, mem-

ory controller, PCI controller) are still active. There is

absolutely no observational evidence that the processor

has changed operational behavior except for two things.

The GX1 draws significantly less core power and the

SUSPA# pin is active while in this state.

5.1.3

CPU Suspend

CPU Suspend is a hardware initiated power management

state. The SUSP# pin is asserted by external hardware

such as an Geode I/O companion. The GX1 processor

asserts the SUSPA# pin to indicate that the processor has

entered CPU Suspend. This state is similar to Suspend-on-

Halt except for its entry and exit method. SUSP# active

causes the processor to enter the state and SUSP# inac-

tive causes its exit. The power savings is identical to Sus-

pend-on-Halt. Also, as in Suspend-on-Halt, the processor

will temporally disable CPU Suspend when there is PCI

master activity.

CPU Suspend can be used for Suspend Modulation. The

Geode I/O companion can be programmed to assert/deas-

sert SUSP# at a programmable frequency and duty cycle.

This has the effect of reducing the average frequency that

the processor is running and thus reduces power con-

sumption and performance. Certain processing activities

(SMI#, Interrupts, and VGA activity) can be monitored by

the Geode I/O companion to temporarily suspend, Sus-

pend Modulation for a programmable amount of time. Sus-

pend modulation programming is explained in detail in the

Geode I/O companion data books such as the CS5530.

GX1 Datasheet(PDF) 177 Page - National Semiconductor (TI)

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