Intel 500 - DATASHEET REV 003 Datasheet page 65

Thermal Specifications
Caution: An under-designed thermal solution that is not able to prevent excessive activation of
the TCC in the anticipated ambient environment may cause a noticeable performance
loss and may affect the long-term reliability of the processor. In addition, a thermal
solution that is significantly under designed may not be capable of cooling the
processor even when the TCC is active continuously.
The Intel Thermal Monitor controls the processor temperature by modulating (starting
and stopping) the processor core clocks when the processor silicon reaches its
maximum operating temperature. The Intel Thermal Monitor uses two modes to
activate the TCC: Automatic mode and on-demand mode. If both modes are activated,
automatic mode takes precedence.
Note: The Intel Thermal Monitor automatic mode must be enabled through BIOS for the
processor to be operating within specifications.
The processor supports an automatic mode called Intel Thermal Monitor 1. This mode is
enabled by writing values to the MSRs of the processor. After automatic mode is
enabled, the TCC activates only when the internal die temperature reaches the
maximum allowed value for operation.
During high temperature situations, Intel Thermal Monitor 1 modulates the clocks by
alternately turning the clocks off and on at a 50% duty cycle. Cycle times are processor
speed-dependent and decreases linearly as processor core frequencies increase. Once
the temperature has returned to a non-critical level, modulation ceases and TCC goes
inactive. A small amount of hysteresis has been included to prevent rapid active/
inactive transitions of the TCC when the processor temperature is near the trip point.
The duty cycle is factory configured and cannot be modified. Also, automatic mode
does not require any additional hardware, software drivers, or interrupt handling
routines. Processor performance is decreased by the same amount as the duty cycle
when the TCC is active.
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 is 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 takes 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 also
includes one ACPI register, one performance counter register, three 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# is not asserted when the processor is in the Stop Grant, Sleep, and Deep
Sleep low-power states (internal clocks stopped.). As a result, the thermal diode
reading must be used as a safeguard to maintain the processor junction temperature
within 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# remains
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