Optical Drive and Library SCSI-2 Command Reference

SCSI Command Overview
Drive Control Commands
Chapter 11-12
Clear Queue 0EH
The drive goes to the BUS FREE phase following successful receipt of the
CLEAR QUEUE message. The drive clears all I/O processes, from all
initiators, in the queue for the specified logical unit from the queue. All
active I/O processes are terminated. The medium may have been altered
by partially executed commands. All pending status and data for that
logical unit for all initiators are cleared. A unit attention condition is
generated for all other initiators with I/O processes that either were
active or were queued for that logical unit. The additional sense code is
set to Command Cleared by Another Initiator.
Queue Tag Messages (20H, 21H, 22H)
The drive supports SIMPLE QUEUE TAG, HEAD OF QUEUE TAG, and
ORDERED QUEUE TAG. The Queue Tag Messages consist of two
consecutive bytes, Message Code (20H, 21H, or 22H) and Queue Tag
(00H-FFH) to distinguish each I/O process. The Queue Tag of each I/O
process must be unique for each I/O process, but the numeric value of a
queue tag has no effect on the order of execution.
The Simple Queue Tag message specifies that the I/O process be placed
in the logical units command queue. The order of the execution may be
altered within the constraints of the queue management algorithm
specified in the control mode page.
Table 1-5 Simple Queue Tag
Byte 7 6 5 4 3 2 1 0
0 Message Code (20H)
1 Queue Tag (00H-FFH)