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Thermal Management Logic and Thermal Monitor Feature
Figure 8. Concept for Clocks under Thermal Monitor Control
PROCHOT#
Normal clock
Internal clock
Duty cycle
control
Resultant
internal clock
4.2.3
Thermal Monitor 2
The processor supports an enhanced Thermal Control Circuit. In conjunction with the
existing Thermal Monitor logic, this capability is known as Thermal Monitor 2. This
enhanced TCC provides an efficient means of reducing the power consumption within
the processor and limiting the processor temperature.
When Thermal Monitor 2 is enabled, and a high temperature situation is detected, the
enhanced TCC will be activated. The enhanced TCC causes the processor to adjust its
operating frequency (by dropping the bus-to-core multiplier to its minimum available
value) and input voltage identification (VID) value. This combination of reduced
frequency and VID results in a reduction in processor power consumption.
A processor enabled for Thermal Monitor 2 includes two operating points, each
consisting of a specific operating frequency and voltage. The first operating point
represents the normal operating condition for the processor.
The second operating point consists of both a lower operating frequency and voltage.
When the TCC is activated, the processor automatically transitions to the new
frequency. This transition occurs very rapidly (on the order of 5 microseconds).
During the frequency transition, the processor is unable to service any bus requests,
all bus traffic is blocked. Edge-triggered interrupts will be latched and kept pending
until the processor resumes operation at the new frequency.
Once the new operating frequency is engaged, the processor will transition to the new
core operating voltage by issuing a new VID code to the voltage regulator. The
voltage regulator must support VID transitions in order to support Thermal Monitor 2.
During the voltage change, it will be necessary to transition through multiple VID
codes to reach the target operating voltage. Each step will be one VID table entry
(i.e., 12.5 mV steps). The processor continues to execute instructions during the
voltage transition. Operation at the lower voltage reduces the power consumption of
the processor, providing a temperature reduction.
Thermal and Mechanical Design Guidelines
33
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