SpeedStep Technology

The initial incarnation of the SpeedStep technology was code-named Geyserville and was quite simplistic compared to the power saving technologies used on the Pentium® M processor (see “Enhanced SpeedStep” on page 1433 for more information).

As implemented on the Pentium® III processor, Intel® Speedstep technology allowed the processor to switch between two core frequencies without resetting the processor or changing the FSB frequency. The processor had two FSB-to-core frequency ratios programmed instead of one (the two values were programmed into the processor when it was manufactured and could not be changed). Low Frequency Mode (LFM) maximized battery life, while High Frequency Mode (HFM) permitted the processor to operate at full speed when the laptop was connected to AC power.

The processor's GHI# input signal controlled which of the two bus ratios was used. After reset, the processor started operation at the lower of the two core frequencies (LFM). The OS transitioned the processor to HFM in the following manner (if the system was connected to AC power):

1.
Transition the processor into the Deep Sleep state (see “The Deep Sleep State” on page 693).

2.
Command the chipset to instruct the system board voltage regulator to raise the operating voltage supplied to the processor core.

3.
Command the chipset to set the processor's GHI# input low.

4.
The processor asserts its VRCHGNG# (Voltage Regulator Change in progress) output while it is making the state change (from LFM to HFM). The chipset monitors this signal and, when the processor deasserts it, the chipset generates an SCI (System Control Interrupt—on an x86-based platform, the SMI# signal usually fulfills this role) to transition the processor out of the Deep Sleep state.

5.
Transition the processor back to the Normal state (see “The Normal State” on page 686).

Transitioning the processor back to LFM was made by reversing these steps.

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