Datasheet

Thermal Specifications
64 Datasheet
5.4 Intel
®
Thermal Monitor
The Intel Thermal Monitor helps control the processor temperature by activating the
TCC (Thermal Control Circuit) when the processor silicon reaches its maximum
operating temperature. The temperature at which the Intel Thermal Monitor activates
the TCC is not user configurable. Bus traffic is snooped in the normal manner and
interrupt requests are latched (and serviced during the time that the clocks are on)
while the TCC is active.
With a properly designed and characterized thermal solution, it is anticipated that the
TCC would only be activated for very short periods of time when running the most
power intensive applications. The processor performance impact due to these brief
periods of TCC activation is expected to be minor and hence not detectable.
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 (TM1). This
mode is enabled by writing values to the MSRs of the processor. After automatic mode
is enabled, the TCC will activate only when the internal die temperature reaches the
maximum allowed value for operation.
During high temperature situations, TM1 will modulate the clocks by alternately turning
the clocks off and on at a 50% duty cycle. Cycle times are processor speed dependent
and will decrease 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 will be 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 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.