82801FB Datasheet, PDF (163/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

Functional Description
5.14.8
5.14.8.1
Thermal Management
The ICH6 has mechanisms to assist with managing thermal problems in the system.
THRM# Signal
The THRM# signal is used as a status input for a thermal sensor. Based on the THRM# signal
going active, the ICH6 generates an SMI# or SCI (depending on SCI_EN). If the THRM_POL bit
is set low, when the THRM# signal goes low, the THRM_STS bit will be set. This is an indicator
that the thermal threshold has been exceeded. If the THRM_EN bit is set, then when THRM_STS
goes active, either an SMI# or SCI will be generated (depending on the SCI_EN bit being set).
The power management software (BIOS or ACPI) can then take measures to start reducing the
temperature. Examples include shutting off unwanted subsystems, or halting the processor.
By setting the THRM_POL bit to high, another SMI# or SCI can optionally be generated when the
THRM# signal goes back high. This allows the software (BIOS or ACPI) to turn off the cooling
methods.
Note: THRM# assertion does not cause a TCO event message in S3 or S4. The level of the signal is not
reported in the heartbeat message.
5.14.8.2
Processor Initiated Passive Cooling
This mode is initiated by software setting the THTL_EN or THTL_DTY bits. Software sets the
THTL_DTY bits to select throttle ratio and THTL_EN bit to enable the throttling.
Throttling results in STPCLK# active for a minimum time of 12.5% and a maximum of 87.5%. The
period is 1024 PCI clocks. Thus, the STPCLK# signal can be active for as little as 128 PCI clocks
or as much as 896 PCI clocks. The actual slowdown (and cooling) of the processor depends on the
instruction stream, because the processor is allowed to finish the current instruction. Furthermore,
the ICH6 waits for the STOP-GRANT cycle before starting the count of the time the STPCLK#
signal is active.
5.14.8.3
THRM# Override Software Bit
The FORCE_THTL bit allows the BIOS to force passive cooling, independent of the ACPI
software (that uses the THTL_EN and THTL_DTY bits). If this bit is set, the ICH6 starts throttling
using the ratio in the THRM_DTY field.
When this bit is cleared, the ICH6 stops throttling, unless the THTL_EN bit is set (indicating that
ACPI software is attempting throttling).
If both the THTL_EN and FORCE_THTL bits are set, then the ICH should use the duty cycle
defined by the THRM_DTY field, not the THTL_DTY field.
5.14.8.4
Active Cooling
Active cooling involves fans. The GPIO signals from the ICH6 can be used to turn on/off a fan.
Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet
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