HP C2246 Technical Reference Manual page 37

executed before the Ordered-Queue command. All Simple-Queue commands received after
an Ordered-Queue command are executed after the Ordered-Queue command.
• Clear Queue Message. Clears from the queue all I/O processes from all initiators in the
queue for the specified logical unit (LUN). All active I/O processes for that LUN are
terminated. All pending status and data for that L UN are cleared. No status or message
is sent for any of the I/O processes. A Unit Attention condition is generated for all other
initiators with I/O processes that either were active or were queued for that target.
The device goes to the Bus Free phase following successful receipt of this message. The
additional sense code for the Unit Attention is: Commands Cleared by Another Initiator.
• Abort Tag Message. Instructs the target to abort a tagged command. The target clears
~he
current I/O process. If the target has already started execution of the I/O process, the
execution is halted .. Any pending status or data for the I/O process is cleared and no status
or ending message is sent to the initiator. Pending status, data, and commands for other
active or queued I/O processes are not affected.
Command queuing is activated by the Target when the Initiator precedes a command with
a one-byte queue tag message that specifies the type of command queuing, followed by a
one-byte queue tag value that uniquely defines the I/O process. The queue tag message values
are:
20H
=
Head of Queue Tag
21H
=
Simple Queue Tag
22H
=
Ordered Queue Tag
A queue tag value can be any hex value from OOh to FFh. An Initiator can assign 256 queue
tags to a LUN. A queue tag value becomes available for reassignment after the I/O process it
is assigned to is completed. If more than one command with the same queue tag value is sent
to a LUN, all commands are aborted for that initiator.
The Clear Queue and Abort Tag operations are activated by one-byte messages with no
follow-on values. These message formats are:
OEH
=
Clear Queue
ODH = Abort Tag
If an Initiator sends a tagged command to a Target when the command queue is full, the
Target will send a Queue Full status to the Initiator. The Initiator should wait a period of
time, and then send the command again.
Untagged commands are also accepted by the C2244/45/46/47 with the following restrictions:
• An untagged command sent by an Initiator will not be accepted if there are any other
commands (tagged or untagged) in the queue that were sent by the same Initiator.
• A tagged command sent by an Initiator will not be accepted if there is an untagged
command already in the queue that was sent by the same Initiator.
The C2244/45/46/47 will clear the queue in either case.
Note
Error recovery is an exception to the above restrictions because the Initiator is
required to send an untagged REQUEST SENSE command if an error occurs
while a Target is executing a command.
Product Features 3··5