Intel Pentium M Processor with 2-MB L2 Cache and 533-MHz Front Side Bus Datasheet

Datasheet 63
Thermal Specifications and Design Considerations
Note: The Intel Thermal Monitor automatic mode must be enabled through BIOS for the processor to be
operating within specifications.
There are two automatic modes called Intel Thermal Monitor 1 and Intel Thermal Monitor 2. These
modes are selected by writing values to the Model Specific Registers (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.
Likewise, when Intel Thermal Monitor 2 is enabled, and a high temperature situation exists, the
processor will perform an Enhanced Intel SpeedStep Technology transition to a lower operating
point. When the processor temperature drops below the critical level, the processor will make an
Enhanced Intel SpeedStep Technology transition to the last requested operating point. Intel
Thermal Monitor 2 is the recommended mode on Pentium M Processors.
If a processor load based Enhanced Intel SpeedStep Technology transition (through MSR write) is
initiated when an Intel Thermal Monitor 2 period is active, there are two possible results:
1.If the processor load based Enhanced Intel SpeedStep Technology transition target frequency is
higher than the Intel Thermal Monitor 2 transition based target frequency, the processor load-
based transition will be deferred until the Intel Thermal Monitor 2 event has been completed.
2.If the processor load-based Enhanced Intel SpeedStep Technology transition target frequency is
lower than the Intel Thermal Monitor 2 transition based target frequency, the processor will
transition to the processor load-based Enhanced Intel SpeedStep Technology target frequency
point.
When Intel Thermal Monitor 1 is enabled, and a high temperature situation exists, the clocks will
be modulated 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, 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.