Datasheet

86 Dual-Core Intel
®
Itanium
®
Processor 9000 and 9100 Series Datasheet
System Management Feature Specifications
6.5 Thermal Sensing Device
The Dual-Core Intel Itanium processor 9000 and 9100 series thermal sensing device
provides a means of acquiring thermal data from the processor. The accuracy of the
thermal reading is expected to be better than ±5 °C. The thermal sensing device is
composed of control logic, SMBus interface logic, a precision analog to digital converter,
and a precision current source. The thermal sensing device drives a small current
through a thermal diode located on the processor core and measures the voltage
generated across the thermal diode by the current. With this information, the thermal
sensing device computes a byte of temperature data. Software running on the
processor or on a micro-controller can use the temperature data from the thermal
sensing device to thermally manage the system.
The thermal sensing device provides a register with a data byte (seven bits plus sign)
which contains a value corresponding to the sampled output of the thermal diode in the
processor core. The value of the byte read from the thermal sensor is always higher
than the actual processor core temperature; therefore, the offset from the reading
needs to be subtracted to obtain an accurate reading of the processor core
temperature. This data can be used in conjunction with the upper temperature
reference byte (provided in the Processor Information ROM) for thermal management
purposes. The temperature data from the thermal sensor can be read out digitally
using an SMBus read command (see Section 6.6). The thermal sensor detects when
SMBus power is applied to the processor, and resets itself at power-up.
The thermal sensing device also contains alarm registers to store thermal reference
threshold data. These values can be individually programmed on the thermal sensor. If
the measured temperature equals or exceeds the alarm threshold value, the
appropriate bit is set in the thermal sensing device status register, which is also
brought out to the processor system bus via the THRMALERT# signal (see
Section 6.1.1 for more details). At power-up, the appropriate alarm register values
need to be programmed into the thermal sensing device via the SMBus. It is
recommended that the upper thermal reference threshold byte (provided in the
processor information ROM) be used for setting the upper threshold value in the alarm
register. To account for the offset inherent in the thermal sensing device reading, the
actual programmed value of the upper threshold value in the alarm register should be
the sum of the upper thermal reference threshold byte and the thermal calibration
offset byte (both provided in the PIROM).
When polling the thermal sensing device on the processor to read the processor
temperatures, it is recommended that the polling frequency be every 0.5 to 1 second.
Table 6-6. Random Address Read SMBus Packet
S
Device
Address
W A
Data
Address
AS
Device
Address
R A Data /// P
17 bits1
18 bits117 bits11 8 bits 1 1
Table 6-7. Byte Write SMBus Packet
S
Device
Address
W A
Data
Address
ADataAP
17 bits0
18 bits18 bits11