Features
6.2.5
Sleep State—State 5
The Sleep state is a very low power state in which the processor maintains its context, maintains
the phase-locked loop (PLL), and has stopped all internal clocks. The Sleep state can be entered
only from Stop-Grant state. Once in the Stop-Grant state, the processor will enter the Sleep state
upon the assertion of the SLP# signal. The SLP# pin should be asserted only when the processor is
in the Stop-Grant state. SLP# assertions while the processor is not in the Stop-Grant state is out of
specification, and may result in unapproved operation.
Snoop events that occur while in Sleep State or during a transition into or out of Sleep state will
cause unpredictable behavior.
In the Sleep state, the processor is incapable of responding to snoop transactions or latching
interrupt signals. No transitions or assertions of signals (with the exception of SLP# or RESET#)
are allowed on the system bus while the processor is in Sleep state. Any transition on an input
signal before the processor has returned to Stop-Grant state will result in unpredictable behavior.
If RESET# is driven active while the processor is in the Sleep state and is held active as specified
in the RESET# pin specification, the processor will reset itself, ignoring the transition through
Stop-Grant State. If RESET# is driven active while the processor is in the Sleep State, the SLP#
and STPCLK# signals should be deasserted immediately after RESET# is asserted to ensure that
the processor correctly executes the Reset sequence.
Once in the Sleep state, the SLP# pin must be de-asserted if another asynchronous system bus
event needs to occur. The SLP# pin has a minimum assertion of one BCLK period.
When the processor is in Sleep state, it will not respond to interrupts or snoop transactions.
6.3
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
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Intel® Pentium® 4 Processor on 0.13 Micron Process Datasheet
INTEL [ INTEL ]
