Mobile Intel Pentium 4 Processor Supporting Hyper-Threading Technology on 90-nm Process Technology

Mobile Intel® Pentium® 4 Processor Supporting Hyper-Threading Technology on 90-nm Process Technology Datasheet 61
Thermal Specifications and Design Considerations
5.2 Processor Thermal Features
5.2.1 Intel Thermal Monitor
The Intel Thermal Monitor feature helps control the processor temperature by activating the TCC
when the processor silicon reaches its maximum operating temperature. The TCC reduces
processor power consumption as needed by modulating (starting and stopping) the internal
processor core clocks. The Intel Thermal Monitor or Intel Thermal Monitor 2 feature must be
enabled for the processor to be operating within specifications. The temperature at which the
Intel Thermal Monitor activates the thermal control circuit is not user configurable and is not
software visible. 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.
When the Intel Thermal Monitor feature is enabled, and a high temperature situation exists (i.e.
TCC is active), the clocks will be modulated by alternately turning the clocks off and on at a duty
cycle specific to the processor (typically 30-50%). Clocks often will not be off for more than 3.0
microseconds when the TCC is active. Cycle times are processor speed dependent and will
decrease as processor core frequencies increase. A small amount of hysteresis has been included to
prevent rapid active/inactive transitions of the TCC when the processor temperature is near its
maximum operating temperature. Once the temperature has dropped below the maximum
operating temperature, and the hysteresis timer has expired, the TCC goes inactive and clock
modulation ceases.
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 so minor that it would be immeasurable. 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 in some cases may result in a T
C
that exceeds the
specified maximum temperature 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. Consult your Intel field sales representative
for information on designing a thermal solution.
The duty cycle for the TCC, when activated by the Thermal Monitor, is factory configured and
cannot be modified. The Thermal Monitor does not require any additional hardware, software
drivers, or interrupt handling routines.
5.2.2 Thermal Monitor 2
The Mobile processor also supports an additional power reduction capability known as Thermal
Monitor 2. This mechanism provides an efficient means for limiting the processor temperature by
reducing the power consumption within the processor. Consult your Intel field sales representative
for information on determining whether a given processor supports Thermal Monitor 2 and for
configuration information.
When the Intel Thermal Monitor 2 is enabled, and a high temperature situation is detected, the
Thermal Control Circuit (TCC) will be activated. The TCC causes the processor to adjust its
operating frequency (via the bus multiplier) and input voltage (via the VID signals). This
combination of reduced frequency and VID results in a reduction to the processor power
consumption.