Datasheet
83
Thermal Specifications and Design Considerations
and cannot be modified. Also, automatic mode does not require any additional hardware, software
drivers, or interrupt handling routines. Processor performance will be decreased by the same
amount as the duty cycle when the TCC is active, however, with a properly designed and
characterized thermal solution the TCC most likely will never be activated, or only will be
activated briefly during the most power intensive applications.
The TCC may also be activated via On-Demand mode. If bit 4 of the ACPI Intel Thermal Monitor
Control Register is written to a 1, the TCC will be activated immediately, independent of the
processor temperature. When using On-Demand mode to activate the TCC, the duty cycle of the
clock modulation is programmable via bits 3:1 of the same ACPI Intel Thermal Monitor Control
Register. In automatic mode, the duty cycle is fixed at 50% on, 50% off, however in On-Demand
mode, the duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in
12.5% increments. On-Demand mode may be used at the same time Automatic mode is enabled,
however, if the system tries to enable the TCC via On-Demand mode at the same time automatic
mode is enabled
and
a high temperature condition exists, automatic mode will take precedence.
An external signal, PROCHOT# (processor hot) is asserted when the processor detects that its
temperature is above the thermal trip point. Bus snooping and interrupt latching are also active
while the TCC is active.
Besides the thermal sensor and thermal control circuit, the Intel Thermal Monitor feature also
includes one ACPI register, one performance counter register, three model specific registers
(MSR), and one I/O pin (PROCHOT#). All are available to monitor and control the state of the
Intel Thermal Monitor feature. The Intel Thermal Monitor can be configured to generate an
interrupt upon the assertion or deassertion of PROCHOT#.
Note:
PROCHOT# will not be asserted when the processor is in the Stop Grant, Sleep, Deep Sleep, and
Deeper Sleep low power states (internal clocks stopped), hence the thermal diode reading must be
used as a safeguard to maintain the processor junction temperature within the 100 °C (maximum)
specification. If the platform thermal solution is not able to maintain the processor junction
temperature within the maximum specification, the system must initiate an orderly shutdown to
prevent damage. If the processor enters one of the above low power states with PROCHOT#
already asserted, PROCHOT# will remain asserted until the processor exits the Low Power state
and the processor junction temperature drops below the thermal trip point.
If automatic mode is disabled, the processor will be operating out of specification. Regardless of
enabling the automatic or On-Demand modes, in the event of a catastrophic cooling failure, the
processor will automatically shut down when the silicon has reached a temperature of
approximately 125 °C. At this point the FSB signal THERMTRIP# will go active. THERMTRIP#
activation is independent of processor activity and does not generate any bus cycles. When
THERMTRIP# is asserted, the processor core voltage must be shut down within the time specified
in
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