Intel
®
Xeon
®
Processor C5500/C3500 Series and LGA1366 Socket
August 2010
Thermal/Mechanical Design Guide
Order Number: 323107-002US
50
Thermal Specifications
6.2.2.2
Clock Modulation
Clock modulation is performed by alternately turning the clocks off and on at a duty
cycle specific to the processor (factory configured to 37.5% on and 62.5% off). The
period of the duty cycle is configured to 32 microseconds when the TCC is active. Cycle
times are independent of processor frequency. 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. Clock modulation is
automatically engaged as part of the TCC activation when the Frequency/VID targets
are at their minimum settings. It may also be initiated by software at a configurable
duty cycle.
6.2.2.3
On-Demand Mode
The processor provides an auxiliary mechanism that allows system software to force
the processor to reduce its power consumption. This mechanism is referred to as “On-
Demand” mode and is distinct from the Adaptive Thermal Monitor feature. On-Demand
mode is intended as a means to reduce system level power consumption. Systems
utilizing the Intel
®
Xeon
®
Processor 5500 Series must not rely on software usage of
this mechanism to limit the processor temperature. If bit 4 of the
IA32_CLOCK_MODULATION MSR is set to a ‘1’, the processor will immediately reduce
its power consumption via modulation (starting and stopping) of the internal core clock,
independent of the processor temperature. When using On-Demand mode, the duty
cycle of the clock modulation is programmable via bits 3:1 of the same
IA32_CLOCK_MODULATION MSR. 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 in conjunction with the Adaptive Thermal Monitor;
however, if the system tries to enable On-Demand mode at the same time the TCC is
engaged, the factory configured duty cycle of the TCC will override the duty cycle
selected by the On-Demand mode.
6.2.2.4
PROCHOT# Signal
An external signal, PROCHOT# (processor hot), is asserted when the processor core
temperature has reached its maximum operating temperature. If Adaptive Thermal
Monitor is enabled (it must be enabled for the processor to be operating within
specification), the TCC will be active when PROCHOT# is asserted. The processor can
be configured to generate an interrupt upon the assertion or de-assertion of
PROCHOT#.
The PROCHOT# signal is bi-directional in that it can either signal when the processor
(any core) has reached its maximum operating temperature or be driven from an
external source to activate the TCC. The ability to activate the TCC via PROCHOT# can
provide a means for thermal protection of system components.
As an output, PROCHOT# will go active when the processor temperature monitoring
sensor detects that one or more cores has reached its maximum safe operating
temperature. This indicates that the processor Thermal Control Circuit (TCC) has been
activated, if enabled. As an input, assertion of PROCHOT# by the system will activate
the TCC for all cores. TCC activation when PROCHOT# is asserted by the system will
result in the processor immediately transitioning to the minimum frequency and
corresponding voltage (using Freq/VID control). Clock modulation is not activated in
this case. The TCC will remain active until the system de-asserts PROCHOT#.
