Thermtrip# Signal; Platform Environment Control Interface (Peci); Introduction - Intel X3350 - Xeon 2.66 Ghz 12M L2 Cache 1333MHz FSB LGA775 Quad-Core Processor Design Manual

PROCHOT# can allow VR thermal designs to target maximum sustained current instead
of maximum current. Systems should still provide proper cooling for the VR, and rely
on PROCHOT# only as a backup in case of system cooling failure. The system thermal
design should allow the power delivery circuitry to operate within its temperature
specification even while the processor is operating at its Thermal Design Power.
With a properly designed and characterized thermal solution, it is anticipated that
PROCHOT# will only be asserted for very short periods of time when running the most
power intensive applications. An under-designed thermal solution that is not able to
prevent excessive assertion of PROCHOT# in the anticipated ambient environment may
cause a noticeable performance loss. Refer to the appropriate platform design guide
and for details on implementing the bi-directional PROCHOT# feature.
6.2.3

THERMTRIP# Signal

Regardless of whether or not Adaptive Thermal Monitor is enabled, in the event of a
catastrophic cooling failure, the processor will automatically shut down when the silicon
has reached an elevated temperature (see the THERMTRIP# definition in the
Datasheet). At this point, the THERMTRIP# signal will go active and stay active as
described in the Datasheet. THERMTRIP# activation is independent of processor
activity. If THERMTRIP# is asserted, processor core voltage (V
within the timeframe defined in the Datasheet. The temperature at which THERMTRIP#
asserts is not user configurable and is not software visible.
6.3

Platform Environment Control Interface (PECI)

6.3.1

Introduction

The Platform Environment Control Interface (PECI) is a one-wire interface that provides
a communication channel between Intel processor and chipset components to external
monitoring devices. The processor implements a PECI interface to allow communication
of processor thermal and other information to other devices on the platform. The
processor provides a digital thermal sensor (DTS) on each core for fan speed control.
The DTS is calibrated at the factory to provide a digital representation of processor
temperature relative PROCHOT# assertion. Instantaneous temperature readings from
the DTS are available via the IA32_TEMP_STATUS MSR; averaged DTS values are read
via the PECI interface.
The PECI physical layer is a self-clocked one-wire bus that begins each bit with a
driven, rising edge from an idle level near zero volts. The duration of the signal driven
high depends on whether the bit value is a logic '0' or logic '1'. PECI also includes
variable data transfer rate established with every message. The single wire interface
provides low board routing overhead for the multiple load connections in the congested
routing area near the processor and chipset components. Bus speed, error checking,
and low protocol overhead provides adequate link bandwidth and reliability to transfer
critical device operating conditions and configuration information.
6.3.1.1 Fan Speed Control with Digital Thermal Sensor
Fan speed control solutions use a value stored in the static variable, T
temperature data which is delivered over PECI (in response to a GetTemp0()
command) is compared to this T
a relative value versus an absolute value. The temperature reported over PECI is
® ®
Intel Xeon Processor C5500/C3500 Series and LGA1366 Socket
Thermal/Mechanical Design Guide
51
reference. The DTS temperature is reported as
CONTROL
Thermal Specifications
) must be removed
CC
. The DTS
CONTROL
August 2010
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