82801BA Datasheet, PDF (148/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.12.9.1
Intel^® SpeedStep™ Technology Processor Requirements
(82801BAM ICH2-M)
Non-Intel^® SpeedStep^™ technology processors use the A20M#, IGNNE#, NMI, and INTR input
signals to determine the multiplier used by the processor’s PLL for the internal clock. In first-
generation Intel^® SpeedStep^™ technology processors, two multiplier values (one for the high
performance state, a second for the low power state) are hard-wired within the processor. The
ICH2-M CPUPERF signal is used to select the processor state, based on ICH2-M control logic.
The operating bus ratio must be available to the programmer and is, therefore, suggested that it be
read in a processor MSR. Also, the processor must return an indication that it is Intel^®
SpeedStep^™ technology enabled, which should be in the form of a status bit in a processor MSR
or in the CPUID register.
The ICH2-M is not capable of determining whether it is attached to a Intel^® SpeedStep^™ or non-
Intel^® SpeedStep^™ processor. When used with a non-Intel^® SpeedStep^™ processor, software
should not write or read the ICH2-M Intel^® SpeedStep^™ registers.
5.12.9.2 Intel^® SpeedStep™ Technology States (82801BAM ICH2-M)
The ICH2-M supports two system-level performance states: Low Power mode and High
Performance mode. Processor states are defined by valid combinations of core voltage levels and
core clock speeds. These processor states can be used to alter the processor and system
performance to conform to conditions of power and environment.
The Low Power mode is used primarily when the system is powered from the battery, with the
purpose being to maximize battery life. Mobile system performance is limited by thermal design
and battery capacity. To improve thermal capacity, active cooling solutions (e.g., a fan can be
used) in addition to a passive cooling solution.
The High Performance mode assume that the mobile system is powered from an external AC/DC
source. The purpose of this state is to maximize performance subject to thermal constraints. The
ICH2-M does not implement any restrictions on entry into High Performance mode. It will
unconditionally transition into High Performance mode upon software command.
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82801BA ICH2 and 82801BAM ICH2-M Datasheet