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User’s Guide 21020285 D
Chapter 8 Details of Usage
Target Mode Usage and SCSI Protocol Handling Page 8 - 15
Disconnect
Privilege
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.
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.
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.