Intel Itanium 2 Processor manual Thermal Sensing Device Supported SMBus Transactions

System Management Feature Specifications

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.

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.

6.6Thermal Sensing Device Supported SMBus Transactions

The thermal sensing device responds to five of the SMBus packet types: write byte, read byte, send byte, receive byte, and alert response address (ARA). The send byte packet is used for sending one- shot commands only. The receive byte packet accesses the register commanded by the last read byte packet. If a receive byte packet was preceded by a write byte or send byte packet more recently than a read byte packet, then the behavior is undefined. Table 6-8through Table 6-12diagram the five packet types. In these tables, ‘S’ represents the SMBus start bit, ‘P’ represents a stop bit, ‘Ack’ represents an acknowledge, and ‘///’ represents a negative acknowledge. The shaded bits are transmitted by the thermal sensor and the unshaded bits are transmitted by the SMBus host controller. Table 6-13shows the encoding of the command byte.

Table 6-8. Write Byte SMBus Packet

S	Address	Write	Ack	Command	Ack	Data	Ack	P
1	7 bits	1	1	8 bits	1	8 bits	1	1

Table 6-9. Read Byte SMBus Packet

S

Address

Write

Ack

Command

Ack

S

Address

Read

Ack

Data

///

P

1

7 bits

1

1

8 bits

1

1

7 bits

1

1

8 bits

1

1

Table 6-10. Send Byte SMBus Packet

S	Address	Write	Ack	Command	Ack	P
1	7 bits	1	1	8 bits	1

Table 6-11. Receive Byte SMBus Packet

S	Address	Read	Ack	Data	///	P
1	7 bits	1	1	8 bits	1	1

Table 6-12. ARA SMBus Packet

S	ARA	Read	Ack	Address	///	P
1	0001 100	1	1	1001 1011	1	1

Datasheet 87