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CS5530A Datasheet

  • CS5530A

  • National Semiconductor [Geode CS5530A I/O Companion Multi-F...

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Geode鈩?CS5530A
Functional Description
(Continued)
3.4.1.6 Suspend Modulation
Suspend Modulation is a derivative of the On and Suspend
states and works by asserting and de-asserting the SUSP#
pin to the CPU for a configurable period and duty cycle. By
modulating the SUSP# pin, an effective reduction in fre-
quency is achieved. Suspend Modulation is the system
power management choice of last resort. However, it is an
excellent choice for thermal management. If the system is
expected to operate in a thermal environment where the
processor could overheat, then Suspend Modulation could
be used to reduce power consumption in the overheated
condition and thus reduce the processor鈥檚 temperature.
When used as a power management state, Suspend Mod-
ulation works by assuming that the processor is idle unless
external activity indicates otherwise. This approach effec-
tively slows down the processor until external activity indi-
cates a need to run at full speed, thereby reducing power
consumption.
Suspend Modulation serves as the primary CPU power
management mechanism when APM or some other power
management software strategy is not present. It can also
act as a backup for situations where the power manage-
ment scheme does not correctly detect an Idle condition in
the system.
In order to provide high-speed performance when needed,
the SUSP# pin modulation can be temporarily disabled any
time system activity is detected. When this happens, the
processor is 鈥渋nstantly鈥?converted to full speed for a pro-
grammed duration. System activities in the CS5530A are
defined in hardware as: any unmasked IRQ, accessing
Port 061h, SMI, and/or accessing the graphics controller.
Since the graphics controller is integrated in the GX-series
processor, the indication of graphics activity is sent to the
CS5530A via the serial link (see Section 3.1.2 "PSERIAL
Pin Interface" on page 45 for more information on serial
link) and is automatically decoded. Graphics activity is
defined as any access to the VGA register space, the VGA
frame buffer, the graphics accelerator control registers and
the configured graphics frame buffer.
The automatic speedup events (IRQ, SMI, and/or graphics)
for Suspend Modulation should be used together with soft-
ware-controlled speedup registers for major I/O events
such as any access to the floppy disk controller, hard disk
drive, or parallel/serial ports, since these are indications of
major system activities. When major I/O events occur, Sus-
pend Modulation can be temporarily disabled using the
procedures described in the following subsections.
Bus master internal (Ultra DMA/33, Audio, USB, or ISA) or
external requests do not directly affect the Suspend Modu-
lation programming.
Configuring Suspend Modulation
Control of the Suspend Modulation feature is accomplished
using the Suspend Modulation OFF Count Register, the
Suspend Modulation ON Count Register, and the Suspend
Configuration Register (F0 Index 94h, 95h, and 96h,
respectively).
The Power Management Enable Register 1 (F0 Index 80h)
contains the enables for the individual activity speedup tim-
ers.
Bit 0 of the Suspend Configuration Register (F0 Index 96h)
enables the Suspend Modulation feature. Bit 1 controls
how SMI events affect the Suspend Modulation feature. In
general this bit should be set to a 1, which causes SMIs to
disable Suspend Modulation until it is re-enabled by the
SMI handler.
The Suspend Modulation OFF and ON Count Registers
(F0 Index 94h and 95h) control two 8-bit counters that rep-
resent the number of 32 碌s intervals that the SUSP# pin is
asserted and then deasserted to the processor. These
counters define a ratio which is the effective frequency of
operation of the system while Suspend Modulation is
enabled.
F
eff
= F
GX86
x
Off Count
On Count + Off Count
The IRQ and Video Speedup Timer Count registers (F0
Index 8Ch and 8Dh) configure the amount of time which
Suspend Modulation is disabled when the respective
events occur.
SMI Speedup Disable
If the Suspend Modulation feature is being used for CPU
power management, the occurrence of an SMI disables the
Suspend Modulation function so that the system operates
at full speed while in SMM. There are two methods used to
invoke this via bit 1 of the Suspend Configuration Register.
If F0 Index 96h[1] = 0: Use the IRQ Speedup Timer (F0
Index 8Ch) to temporarily disable Suspend Modulation
when an SMI occurs.
If F0 Index 96h[1] = 1: Disable Suspend Modulation when
an SMI occurs until a read to the SMI Speedup Disable
Register (F1BAR+Memory Offset 08h).
The SMI Speedup Disable Register prevents VSA technol-
ogy software from entering Suspend Modulation while
operating in SMM. The data read from this register can be
ignored. If the Suspend Modulation feature is disabled,
reading this I/O location has no effect.
Table 3-14 shows the bit formats of the Suspend Modula-
tion related registers
www.national.com
58
Revision 1.1

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