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1.5 UNIT ATTENTION Condition
C141-E167 1 - 19
The INIT can specify 2 error recovery options by the QErr bit of the control mode parameter (Page
A) of the mode select parameters.
When “0” is specified in the QErr bit, the IDD enters any one of a number of sense hold states, and
when this state is released, it continues to execute the commands in the queue. The IDD queues any
commands received from other INITs while it is in the sense hold state, but during this period,
execution of all the commands in the queue is interrupted.
If “1” is specified in the QErr bit, if the IDD enters any one of a number of sense hold states, the
queue is cleared after the sense hold state is released. When the queue is cleared through this
recovery option, the UNIT ATTENTION condition is generated for all the INITs which had their
commands cleared (excluding the INIT that set the sense hold state). The sense code Commands
cleared by another INIT [=2F-00] is set.
Deferred errors are reported for all commands that have already been completed. Therefore, the
queue tag values attached to those commands are not reported.
If a QUEUE TAG message is received by the IDD when tagged commands are prohibited by the
DQue bit of the control mode page, the IDD rejects the message with the MESSAGE REJECT
message processes the accompanying command as an untagged command.
The ABORT TASK SET, ABORT TASK, TARGET RESET or CLEAR TASK SET message is
used to clear some or all of the commands in the queue. See “SCSI Physical Interface
Specifications” for details.
If ‘0001’ is specified in the Queue algorithm modifier of the control mode page, the IDD performs
command reordering processing of commands issued with a SIMPLE message. Reordering
processing is performed with the objective of reducing total processing time for command
processing.
• Conditions for Reordering:
If a command which is the object of reordering is issued by an INIT that permits reordering with
an accompanying SIMPLE message.
• Commands which are Objects of Reordering:
READ, READ EXTENDED, WRITE, WRITE EXTENDED
If an INIT permits command reordering processing, the IDD changes the processing order of the
commands. It is necessary for the INIT to manage concerning the legality of the data, etc.
Section 4.1.7, “Control mode parameters (page code = 0A)” for details of the control mode page.
1.5 UNIT ATTENTION Condition
The UNIT ATTENTION condition is a function used to notify the INIT asynchronously of an event
(status change) that has occurred in the TARG or logical unit.
1.5.1 Generation of the UNIT ATTENTION condition
Events which cause a UNIT ATTENTION condition to be generated are one of the following.