Chapter 8 Details of Usage
Target Mode Usage and SCSI Protocol Handling | Page 8 - 15 |
Disconnect
Privilege
Note
It is also possible to send a command that requires the target device to access another SCSI device before completion of the original command. If the original command did not grant the disconnect privilege, the target will hang waiting for the SCSI bus.
Initiators that access the adapter as a target should allow disconnect and limit the use of the control field’s link bit in their SCSI commands. By not allowing disconnection or using the link bit, the SCSI bus is monopolized by this single command. Any other device wishing to use the bus during this time must wait for it to be released.
Message Handling
On the following pages Message Handling protocol for the adapter is described. There are three areas in which Message Handling is important:
•Message Bytes received from the Initiator
•Status or Message Sequences Sent to the Initiator (by the Host)
•Status or Message Sequences Sent to the Initiator (by the Adapter) Each of these topics is covered in the following pages.
Message Bytes Received from the Initiator
The following paragraphs describe the messages that may be received from an initiator. The expected action is stated and the adapter’s strategy to handle the message is described.
Abort - Clear the current I/O process plus any queued I/O process for this target/LUN. Go to the Bus Free phase after receipt of this message. This message is sent to the host while holding the SCSI bus. It is the responsibility of the host to instruct the adapter to go to the Bus Free phase after all necessary commands are aborted. If only a target exists, go to the Bus Free phase. In this case, do not send this message to the host.
Abort Tag - Clear the current I/O process for this I_T_x nexus. Go to the Bus Free phase after receipt of this message. This message is sent to the host while holding the SCSI bus. It is the responsibility of the host to instruct the adapter to go to the Bus Free phase after all necessary commands are aborted.
Bus Device Reset - Clear all I/O processes on the target side of the system (this is a hard reset condition). Go to the Bus Free phase after receipt of this message. This message is sent to the host while holding the SCSI bus. It is the responsibility of the host to instruct the adapter to go to the Bus Free phase after all necessary commands are aborted.
User’s Guide | 21020285 D |
