RG82855GMESL72L Datasheet, PDF (167/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Power and Thermal Management
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7.3
Enhanced Intel SpeedStep^® Technology Overview
With Enhanced Intel SpeedStep technology the processor core voltage changes and allows true
CPU core frequency changes versus only clock throttling.
Table 42. Enhanced Intel SpeedStep^® Technology Overview
CPU
Intel^® Pentium^® M processor
Benefit Over Non-power
Managed CPU
Additional lower voltages and frequencies
Transition Prompt
OS based on CPU load demand, thermal control, or user event based
CPU Availability
CPU unavailability can be restricted to ~250 µs (CPU dependent) by s/w
7.4
7.4.1
7.4.2
7.5
Internal Thermal Sensor
This section describes the new on-die Thermal sensor capability.
Overview
The Thermal sensor functions are provided below:
Catastrophic Trip Point: This trip point is programmed through the BIOS during initialization.
This trip point is set at the temperature at which the GMCH should be shut down immediately
with minimal software support. The settings for this are lockable.
High Temperature Trip Point: This trip point is nominally 14ºC below the Catastrophic trip
point. The BIOS can be programmed to provide an interrupt when it is crossed in either direction.
Upon the trip event, Hardware Throttling may be enabled when the temperature is exceeded.
Hysteresis Operation
Hysteresis provides a small amount of positive feedback to the Thermal sensor circuit to prevent a
trip point from flipping back and forth rapidly when the temperature is right at the trip point.
External Thermal Sensor Input
An External Thermal sensor with a serial interface may be placed next to DDR SDRAM SO-
DIMM (or any other appropriate platform location), or a remote Thermal Diode may be placed
next to the SO-DIMM (or any other appropriate platform location) and connected to the External
Thermal sensor. Intel advises that the External Thermal sensor contains some form of hysteresis,
since none is provided by the GMCH hardware.
The external sensor can be connected to the ICH4-M via the SMBus interface to allow
programming and setup by BIOS software over the serial interface. The External sensor’s output
Datasheet
167