Intel Itanium 2 Processor Thermal Sensing Device, Current Address Read SMBus Packet, Device Data

System Management Feature Specifications

controller continues to transmit data bytes until it terminates the sequence with a stop. All data bytes will result in an acknowledge from the Scratch EEPROM. If more than eight bytes are written, the internal address will “roll over” and the previous data will be overwritten.

In Table 6-5through Table 6-7, ‘S’ represents the SMBus start bit, ‘P’ represents a stop bit, ‘R’ represents a read, ‘W’ represents a write bit, ‘A’ represents an acknowledge, and ‘///’ represents a negative acknowledge. The shaded bits are transmitted by the processor information ROM or Scratch EEPROM and the bits that are not shaded are transmitted by the SMBus host controller. In the tables the data addresses indicate eight bits. The SMBus host controller should transmit eight bits, but as there are only 128 addresses, the most significant bit is a don’t care.

Table 6-5. Current Address Read SMBus Packet

S	Device	R	A	Data	///	P
	Address
1	7 bits	1	1	8 bits	1	1

Table 6-6. Random Address Read SMBus Packet

S

Device

W

A

Data

A

S

Device

R

A

Data

///

P

Address

Address

Address

1

7 bits

1

1

8 bits

1

1

7 bits

1

1

8 bits

1

1

Table 6-7. Byte Write SMBus Packet

S	Device	W	A	Data	A	Data	A	P
	Address			Address
1	7 bits	0	1	8 bits	1	8 bits	1	1

6.5Thermal Sensing Device

The Itanium 2 processor’s 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 ±3 °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 Itanium 2 processor core. The value of the byte read from the thermal sensor gives an accurate reading of processor core temperature at the time of the reading. 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 Itanium 2 processor system bus via the

86 Datasheet