82598EB Datasheet, PDF (435/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - SMBus Notification Methods
• Receiving a Request Status command from the BMC initiates a status response.
• Status change has occurred and 82598EB is configured to notify the external BMC at one of the
status changes.
• Change in any in the Status Data 1 bits of the Read Status command.
There can be cases where the BMC is hung and therefore not responding to the SMBus notification. The
82598EB has a time-out value (defined in the EEPROM) to avoid hanging while waiting for the
notification response. If the BMC does not respond until the time out expires, the notification is de-
asserted and all pending data is silently discarded.
Note that the SMBus notification time-out value can only be set in the EEPROM, the BMC cannot modify
this value.
5.3.5.1 SMBus Alert and Alert Response Method
The SMBus Alert# (SMBALERT_N) signal is an additional SMBus signal that acts as an asynchronous
interrupt signal to an external SMBus master. 82598EB asserts this signal each time it has a message
that it needs the BMC to read and if the chosen notification method is the SMBus alert method. Note
that the SMBus alert method is an open-drain signal which means that other devices besides the
82598EB can be connected on the same alert pin. As a result, the BMC needs a mechanism to
distinguish between the alert sources.
The BMC can respond to the alert, by issuing an ARA Cycle command, to detect the alert source device.
The 82598EB responds to the ARA cycle with its own SMBus slave address (if it was the SMBus alert
source) and de-asserts the alert when the ARA cycle is completes. Following the ARA cycle, the BMC
issues a read command to retrieve message.
Some BMCs do not implement the ARA cycle transaction. These BMCs respond to an alert by issuing a
Read command to the 82598EB (0xC0/0xD0 or 0xDE). The 82598EB always responds to a Read
command, even if it is not the source of the notification. The default response is a status transaction. If
the 82598EB is the source of the SMBus Alert, it replies the read transaction and then de-asserts the
alert after the command byte of the read transaction.
Note: In SMBus Alert mode, the SMBALERT_N pin is used for notification. In dual-address mode,
both devices generate alerts on events that are independent of each other.
The ARA cycle is a SMBus Receive Byte transaction to SMBus address 0x18. Note that the ARA
transaction does not support PEC. The alert response address transaction format is shown in
Figure 5-7.
1
7
1
1
8
1
1
S
Alert Response Address
Rd
A
Slave Device Address
A
P
0001 100
0
0
1
Figure 5-7. SMBus ARA Cycle Format
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