The SMP packet is received into the port's VL15 receive buffer. It should be noted that if the buffer is currently full—the minimum required buffer depth is one SMP packet—then the inbound SMP is discarded.

The SMP's DLID address is used to route the packet. Based on the address in the DLID field, there are three possible cases:

- DLID = PLID address. This is a directed-route SMP. The receiving port passes the directed-route SMP to port 0's SMI RQ Logic for processing. A detailed description of directed-route SMPs can be found in “Discovery” on page 871.

- DLID contains a unicast address other than switch port 0's assigned address or the PLID address (i.e., FFFFh). In this case, the switch performs a lookup in its Forwarding Table (either the Linear Forwarding Table—see “Linear Forwarding Table (LFT)” on page 669, or the Random Forwarding Table—see “Random Forwarding Table (RFT)” on page 671) and forwards the packet through the selected exit port. If the selected exit port is port 0, then the packet is internally forwarded to the RQ Logic of port 0's SMI or GSI for processing (see the next numbered step).

- DLID contains the LID address assigned to switch port 0. In this case, the packet is internally forwarded to the RQ Logic of port 0's SMI for processing.

Upon the SMP's arrival at switch port 0's SMI RQ Logic, there are two possibilities:

- DLID = PLID. In this case, this is a directed-route SMP, and it its processing is described in “Packet Routing During Discovery” on page 873.

- DLID = port 0's assigned LID address. In this case, the packet processing is described in the steps that follow.

The packet's 256-byte data payload (the SM MAD) is passed to the SMA within the switch for processing.

Refer to Table 28-5 on page 788 and Table 28-6 on page 789. The SMA performs the method specified in the MAD on the specified attribute. The method in an inbound request SMP can be one of the following:

- Get. In response, the SMA reads the contents of the indicated attribute and places its contents in the 64-byte data field of a 256-byte response MAD. The SMA then tells port 0's SMI SQ Logic to transmit the response MAD back to the SM. The method in the response MAD is the GetResp method. See the next numbered step for the remaining actions taken.

- Set. In response, the SMA writes the data contained in the MAD's data field into the indicated attribute, reads it back, and places its contents in the data field of a 256-byte response MAD. The SMA then tells port 0's SMI SQ Logic to transmit the response MAD back to the SM. The method in the response MAD is the GetResp method. See the next numbered step for the remaining actions taken.

- TrapRepress. This tells the SMA to stop repeatedly sending a particular SubnTrap(Notice) MAD. See “Traps” on page 790 for a description of traps and “Switch Transmission of a Trap(Notice) SMP” on page 766. In response, the SMA stops transmitting the specified SubnTrap(Notice) MAD, completing the processing of the MAD. There is no response.

The SMA swaps the LID addresses (SLID and DLID) that were in the request SMP, sets the BTH:DestQP field to QP0 (the SMI), and passes the packet back to the SMI, which, in turn, passes it to the switch port that received the packet (automatically captured in the PortInfo.LocalPortNum attribute element). That port accepts the packet into its VL15 transmit buffer and transmits the packet. The receiving port's Link Layer accepts the response SMP into its VL15 transmit buffer and forwards the response packet back to the SM.

The switch's SMA formulates a 256-byte MAD with the following characteristics:

- Method = Trap.

- AttributeID = Notice.

- The MAD's 64-byte data field contains the Notice attribute indicating the exact type of event being reported to the SM.

The SMA passes the 256-byte MAD to port 0's SMI SQ Logic for transmission.

The SMI SQ Logic sets the response SMP's SLID and DLID as follows:

- SLID = the LID address of switch port 0.

- DLID = the LID address contained in port 0's PortInfo.MasterSMLID attribute element.

The SMI's SQ Logic passes the response SMP to the port 0 Link Layer where the packet's DLID is used to perform a lookup in the switch's Forwarding Table.

The packet is internally forwarded to the switch exit port resulting from the table lookup and is placed in the VL15 transmit buffer of that port's Link Layer.

The packet is then transmitted to the SM.