Detailed CA or Router Handling of SMPs

CA or Router Handling of an Inbound Request SMP

This discussion assumes that the SM has transmitted a request SMP to a device's SMA and it is now being received by a CA or router port. When a CA or a router port's Link Layer receives an inbound request SMP from the SM, it is processed as follows:

1.
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.

2.
The SMP's DLID address may be either one of the receiving port's assigned LID addresses or may be the PLID address. In either case, the packet is passed to the port's SMI RQ Logic for processing. This example assumes that the DLID is set to one of the receiving port's assigned LID addresses.

3.
The packet's 256-byte data payload (the SM MAD) is passed to the SMA within the CA or router for processing.

4.
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 data field of a 256-byte response MAD. The method in the response MAD is the GetResp method. The SMA then passes the response SMP to the SMI SQ Logic of the receiving port to be transmitted back to the SM. See step 5 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 passes the response SMP to the SMI SQ Logic of the receiving port to be transmitted back to the SM. See step 5 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, thereby completing the processing of the MAD. There is no response.

5.
The receiving port's SMI SQ Logic swaps the LID addresses (SLID and DLID) that were in the request SMP, sets the BTH:DestQP field to QP0, and passes the packet the receiving port's Link Layer where it is accepted into the VL15 transmit buffer and is transmitted to the SM.

CA or Router Handling of an Inbound Response SMP

This discussion assumes that the SM resides within or behind the CA or router port and that one of three cases is true:

  • Earlier, the SM had send a request SMP to a remote device port. The destination device's SMA processed the request SMP and has now transmitted a response SMP back to the CA or router port behind which the SM resides.

  • Another SM has sent a SubnGet(SMInfo) or a SubnSet(SMInfo) request packet to this SM.

  • A device has experienced an event that it wishes to notify the SM of and has sent a SubnTrap(Notice) SMP.

When the CA or router port's Link Layer receives the inbound response SMP from the remote device's SMA, it is processed as follows:

1.
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.

2.
The SMP's DLID address either may be one of the receiving port's assigned LID addresses or may be the PLID address. In either case, the packet is passed to the port's SMI RQ Logic for processing. This example assumes that the DLID is set to one of the receiving port's assigned LID addresses.

3.
This is a response SMP for the SM. The packet's 256-byte data payload (the SM response MAD) either may be:

- passed to the device's SMA which, in turn, passes it to the SM, or

- passed directly to the SM.

4.
The response MAD is one of the following (as indicated by its method):

- A SubnGetResp returning the data read from the target attribute. This is the appropriate response for a Get or a Set operation.

- A SubnTrap(Notice). A device has experienced an event that it wishes to inform the SM of and has sent this SubnTrap(Notice) SMP.

5.
In either case, the SM has now received the information.

CA or Router Handling of an Outbound Request SMP

This discussion assumes that the SM resides within or behind the CA or router and that it wants a remote device's SMA to perform a specified method on a specified attribute.

To accomplish the transmission of the request SMP, the following actions are taken:

  1. The SM formulates the 256-byte request MAD. The specified method is one of the following:

    - Get. A read of a device attribute. In this case, the request MAD's data field is na.

    - Set. A write of a device attribute. In this case, the request MAD's data field contains the data to be written into the specified device attribute.

    - TrapRepress. Tells a device that is repetitively sending the same SubnTrap(Notice) SMP to stop doing so.

  2. The SM may either:

    - pass the request MAD to the local device's SMA which, in turn, passes it to the local CA or router port's SMI SQ Logic indicated by the SM, or

    - pass the request MAD directly to the CA or router port's SMI SQ Logic for transmission.

  3. In either case, the CA or router port's SMI SQ Logic encapsulates the 256-byte request MAD in an SMP and sends it to its associated local port for transmission.

  4. The port's Link Layer accepts the packet into its VL15 transmit buffer.

  5. The packet is transmitted.

CA or Router Transmission of SubnTrap(Notice) SMP

A detailed description of Traps can be found in “Traps” on page 790. When a CA or a router experiences an internal event that the SM must be informed of (e.g., a port's Link Layer detects that its physical link transitions from the Down to the Up state), the following steps are taken:

1.
The CA's or router'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.

2.
The SMA passes the 256-byte MAD to the affected port's SMI SQ Logic for transmission.

3.
The SMI SQ Logic sets the response SMP's SLID and DLID as follows:

- SLID = the transmitting port's LID address.

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

4.
The SMI's SQ Logic passes the response SMP to port's Link Layer and the packet is accepted into the VL15 transmit buffer.

5.
The packet is then transmitted to the SM.

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