Intel Xeon Processor with 800 MHz System Bus Thermal/Mechanical Design Guide

Intel® Xeon™ Processor with 800 MHz System Bus Thermal/Mechanical Design Guidelines 75
Processor Thermal Management Logic and Thermal Monitor Features
Performance counter registers, status bits in model specific registers (MSRs), and the PROCHOT#
output pin are available to monitor and control the Thermal Monitor behavior.
F.1.3 Operation and Configuration
To maintain compatibility with previous generations of processors, which have no integrated
thermal logic, the TCC portion of Thermal Monitor is disabled by default. During the boot
process, the BIOS must enable the TCC; or a software driver may do this after the operating system
has booted. Thermal Monitor or Thermal Monitor 2 feature must be enabled for the
processor to remain within specification.
The TCC feature can be configured and monitored in a number of ways. OEMs are expected to
enable the TCC while using various registers and outputs to monitor the processor thermal status.
The TCC is enabled by the BIOS setting a bit in an MSR (model specific register). Enabling the
TCC allows the processor to maintain a safe operating temperature without the need for special
software drivers or interrupt handling routines. When the TCC has been enabled, processor power
consumption will be reduced within a few hundred clock cycles after the thermal sensor detects a
high temperature, i.e. PROCHOT# assertion. The TCC and PROCHOT# transition to inactive
once the temperature has been reduced below the thermal trip point, although a small time-based
hysteresis has been included to prevent multiple PROCHOT# transitions around the trip point.
External hardware can monitor PROCHOT# and generate an interrupt whenever there is a
transition from active-to-inactive or inactive-to-active. PROCHOT# can also be configured to
generate an internal interrupt which would initiate an OEM supplied interrupt service routine.
Regardless of the configuration selected, PROCHOT# will consistently indicate the thermal status
of the processor.
The TCC can also be manually activated using an on-demand mode.
F.1.4 Thermal Monitor 2
The Intel Xeon Processor with 800 MHz System Bus also supports an enhanced TCC that works in
conjunction with the existing Thermal Monitor logic. This capability is known as Thermal
Monitor 2. This improved TCC provides a more efficient means for limiting the processor
temperature by reducing the power consumption within the processor.
Figure F-28. Concept for Clocks under Thermal Monitor Control
PROCHOT#
N
ormal clock
Core clock w/
TM2 Engaged
VID w/ TM2
Engaged