CHAPTER 3. IPMI INTERFACES
Message tracking is relatively simple, but difficult to understand from the spec. This section should clear that up.
Messages sent from the system interface to the IPMB interface do not have to be tracked. Instead, the sender sets the requester (source) LUN to 2. In the response, the responder will thus set the requester (destination) LUN to 2. If an MC receives a message with a destination LUN of 2, it will route it back to the system interface. Simple to do and no state is required in the MC.
Other channels cannot do this. They must instead rely on message tracking to handle the responding. With message tracking, the MC reformats the message with its own information and remembers the original message information. When the response comes back, the MC will restore the original information in the response. Note that the sender must still format the message properly for the destination channel.
Asyncronous messages to the system interfaces (ones with the destination LUN set to 2), both commands and responses, have no direct route to be sent up the system interface. Instead, they go into the receive message queue and the software is informed through the system interface that something is in the queue. The software must then fetch the message from the queue using the Get Message command described in table 3.5.
Request - Response 0
Completion code Channel information, bits are: 0-4 - Channel number 4-7 - Inferred privilege level for the message. Table 3.18 describes the privilege levels. If the message is received from a session-oriented channel, this will generally be set to the maximum privilege level of the session. If per-message authentication is enabled, this will be set to User privilege for unauthenticated messages. The privilege will be then lowered based on the privilege limit set by the Set Session Privilege Level command. For messages from sessionless channels, this will always be set to “None”. Privilege levels are:
- None (unspecified)
Message data. The format depends on the channel type. See the section on the specific channel type for more information. Table 3.5: Get Message Command, NetFN App (06h), Cmd 33h