SC1100 datasheet(138/348 Pages) NSC

138 / 348 page

www.national.com

138

Revision 1.1

Core Logic Module (Continued)

5.2.10.1 APM Support

Many notebook computers rely solely on an Advanced

Power Management (APM) driver for enabling the operat-

ing system to power-manage the CPU. APM provides sev-

eral

services

which

enhance

the

system

power

management; but in its current form, APM is imperfect for

the following reasons:

• APM is an OS-specific driver, and may not be available

for some operating systems.

• Application support is inconsistent. Some applications in

foreground may prevent Idle calls.

• APM does not help with Suspend determination or

peripheral power management.

The Core Logic module provides two entry points for APM

support:

• Software CPU Suspend control via the CPU Suspend

Command register (F0 Index AEh).

• Software SMI entry via the Software SMI register (F0

Index D0h). This allows the APM BIOS to be part of the

SMI handler.

5.2.10.2 CPU Power Management

The three greatest power consumers in a system are the

display, the hard drive, and the CPU. The power manage-

ment of the first two is relatively straightforward and is dis-

cussed

Section

5.2.10.3

"Peripheral

Power

Management" on page 139.

APM, if available, is used primarily by CPU power manage-

ment since the operating system is most capable of report-

ing the Idle condition. Additional resources provided by the

Core Logic module supplement APM by monitoring exter-

nal activity and power managing the CPU based on the

system demands. The two processes for power managing

the CPU are Suspend Modulation and 3V Suspend.

Suspend Modulation

Suspend Modulation works by asserting and deasserting

the internal SUSP# signal to the GX1 module for config-

urable durations. When SUSP# is asserted to the GX1

module, it enters an Idle state during which time the power

consumption is significantly reduced. Even though the PCI

clock is still running, the GX1 module stops the clocks to its

core when SUSP# is asserted. By modulating SUSP# a

reduced frequency of operation is achieved.

The Suspend Modulation feature works by assuming that

the GX1 module is Idle unless external activity indicates

otherwise. This approach effectively slows down the GX1

module until external activity indicates a need to run at full

speed,

thereby

reducing

power

consumption.

This

approach is the opposite of that taken by most power man-

agement schemes in the industry, which run the system at

full speed until a period of inactivity is detected, and then

slows down. Suspend Modulation, the more aggressive

approach, yields lower power consumption.

Suspend Modulation serves as the primary CPU power

management mechanism when APM is not present. It also

acts as a backup for situations where APM does not cor-

rectly detect an Idle condition in the system.

To provide high-speed performance when needed, SUSP#

modulation is temporarily disabled any time system activity

is detected. When this happens, the GX1 module is

“instantly” converted to full speed for a programmed dura-

tion. System activities in the Core Logic module are

asserted as: any unmasked IRQ, accessing Port 061h, any

asserted SMI.

The automatic speedup events (IRQ) for Suspend Modula-

tion should be used together with software-controlled

speedup registers for major I/O events such as any access

to the FDC, HDD, or parallel/serial ports, since these are

indications of major system activities. When major I/O

events occur, Suspend Modulation should be temporarily

disabled using the procedures described in the Power

Management registers in the following subsections.

If a bus master (UltraDMA/33, Audio, USB) request occurs,

the GX1 module automatically deasserts SUSPA# and

grants the bus to the requesting bus master. When the bus

master deasserts REQ#, SUSPA# reasserts. This does not

directly affect the Suspend Modulation programming.

Configuring Suspend Modulation: Control of the Sus-

pend Modulation feature is accomplished using the Sus-

pend Modulation and Suspend Configuration registers (F0

Index 94h and 96h, respectively).

The Power Management Enable Register 1 at F0 Index 80h

on page 177 contains the Global Power Management bit

(Bit 0). The global power management bit must be enabled

for Suspend Modulation and all other power management

resources to function.

Bit 0 of the Suspend Configuration register enables the

Suspend Modulation feature. Bit 1 controls how SMI events

affect the Suspend Modulation feature. In general this bit

should be set to 1, which causes SMIs to disable Suspend

Modulation until it is re-enabled by the SMI handler.

The Suspend Modulation register controls two 8-bit

counters that represent the number of 32 µs intervals that

the internal SUSP# signal is asserted and then deasserted

to the GX1 module. These counters define a ratio which is

the effective frequency of operation of the system while

Suspend Modulation is enabled.

The IRQ Speedup Timer Count register (F0 Index 8Ch)

configures the amount of time which Suspend Modulation

is disabled when the event occurs.

Feff = FGX1 x

Asserted Count

Asserted Count + Deasserted Count

SC1100 Datasheet(PDF) 138 Page - National Semiconductor (TI)

SC1100 Datasheet(HTML) 138 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL