WCM Forum - P4, ab welcher temperatur regelt er runter?

Auszug aus den Intel P4 Datasheets
(http://developer.intel.com/design/pe...s/29864311.pdf)

Zitat:

Thermal Monitor

The Thermal Monitor feature helps control the processor temperature by activating the Thermal
Control Circuit (TCC) when the processor silicon reaches its maximum operating temperature. The
TCC reduces processor power consumption by modulating (starting and stopping) the internal
processor core clocks. The Thermal Monitor feature must be enabled for the processor to be
operating within specifications. The temperature at which 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 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 µs
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 TC 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. Refer to the Intel® Pentium® 4 Processor
with 512-KB L2 Cache on 0.13 Micron Process Thermal Design Guidelines 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.
The TCC may also be activated via On-Demand mode. If bit 4 of the ACPI 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 Thermal Monitor Control
Register. In automatic mode, the duty cycle is fixed. 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, the duty cycle of the automatic mode will override the
duty cycle selected by the On-Demand mode.
An external signal, PROCHOT# (processor hot), is asserted when the processor detects that its
temperature is at the thermal trip point. Bus snooping and interrupt latching are also active while
the TCC is active. The temperature at which the thermal control circuit activates is not user
configurable and is not software visible.
Besides the thermal sensor and TCC, the Thermal Monitor feature also includes one ACPI register,
performance monitoring logic, bits in three model specific registers (MSR), and one I/O pin
(PROCHOT#). All are available to monitor and control the state of the Thermal Monitor feature.
Thermal Monitor can be configured to generate an interrupt upon the assertion or de-assertion of
PROCHOT#.
If automatic mode is disabled, the processor will be operating out of specification. Regardless of
enabling of the automatic or On-Demand modes, in the event of a catastrophic cooling failure the
processor automatically shuts down when the silicon has reached a temperature of approximately
135 °C. At this point the system bus signal THERMTRIP# goes active and stays active until
RESET# has been initiated. THERMTRIP# activation is independent of processor activity and
does not generate any bus cycles. If THERMTRIP# is asserted, processor core voltage (VCC) must
be removed within 0.5 seconds.

Laut Tabelle (ebenfalls in den Specs) ist TC max typischerweise zwischen 70-75°