Intel Celeron Processor in the 478-Pin Package at 1.80 GHz Datasheet

Datasheet 87
Intel
®
Celeron
®
Processor in the 478-Pin Package
7.3 Thermal Monitor
The Thermal Monitor feature found in the Celeron processor in the 478-pin package allows system
designers to design lower cost thermal solutions without compromising system integrity or
reliability. By using a factory-tuned, precision on-die thermal sensor, and a fast acting thermal
control circuit (TCC), the processor, without the aid of any additional software or hardware, can
keep the processor’s die temperature within factory specifications under nearly all conditions.
Thermal Monitor thus allows the processor and system thermal solutions to be designed much
closer to the power envelopes of real applications, instead of being designed to the much higher
maximum processor power envelopes.
Thermal Monitor controls the processor temperature by modulating the internal processor core
clocks. The processor clocks are modulated when the TCC is activated. Thermal Monitor uses two
modes to activate the TCC: Automatic mode and On-Demand mode. Automatic mode is required
for the processor to operate within specifications and must first be enabled via BIOS. Once
automatic mode is enabled, the TCC will activate only when the internal die temperature is very
near the temperature limits of the processor. When TCC 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 50% duty cycle. Clocks will not be off for more than 3 µs when TCC is active.
Cycle times are processor speed dependent and will decrease linearly 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 the trip point. Once the temperature
has returned to a non-critical level, and the hysteresis timer has expired, modulation ceases and
TCC goes inactive. Processor performance will be decrease by ~50% when the TCC is active
(assuming a 50% duty cycle), however, with a properly designed and characterized thermal
solution the TCC most likely will only be activated briefly when the system is near maximum
temperature and during the most power intensive applications.
For automatic mode, the 50% duty cycle is factory configured and cannot be modified. Also,
automatic mode 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 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, the 50% 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 at any time the TCC is active (either in
automatic or On-Demand mode). 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 thermal control circuit, the Thermal Monitor feature also includes
one ACPI register, one performance counter register, 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# (i.e., upon the activation/deactivation of TCC).