Head Of Queue Tag; Restore Pointers; Save Data Pointers; Synchronous Data Transfer Request - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
Check Condition status. The sense key shall be set to Aborted Task and the additional sense code shall be set
to Overlapped Tasks Attempted. Only one status is returned.
Note. For each logical unit on each target, each initiator has up to 256 task tags to assign to tasks. A task tag
becomes available for reassignment when the task ends. Typically drives to which this specification
applies queue up to 64 tasks concurrently for up to seven initiators on the bus. There could be 64 task
tags for one initiator, or the 64 can be divided among the seven possible initiators, not necessarily
evenly. See individual drive's Product Manual, Volume 1, for number of task tags supported.
The appropriate task tag message shall be sent immediately following the Identify message and within the
same message phase to establish the I T L Q nexus for the task. Only one I T L Q nexus may be established
during a connection. If a Task Attribute message is not sent, then only an I T L nexus is established for the task
(untagged command).
If a target attempts to reconnect using an invalid task tag, then the initiator should respond with an Abort Task
message.
• Linked Command Complete (0Ah)
The Linked Command Complete message is sent from a target to an initiator to indicate that the execution of
a linked command has completed and that status has been sent. The initiator shall then set the pointers to
the initial state for the next linked command.
• Linked Command Complete (with Flag) (0Bh)
The Linked Command Complete (with Flag) message is sent from a target to an initiator to indicate that the
execution of a linked command (with the flag bit set to one) has completed and that status has been sent.
The initiator shall then set the pointers to the initial state of the next linked command.
• Head of Queue (21h)
The Head of Queue task attribute message specifies that the task be placed first in that logical unit's task set
for execution. A task already being executed by the target shall not be preempted. A subsequent task
received with a Head of Queue message shall be placed at the head of the task set queue for execution in
last-in, first-out order.
• Ordered Task (22h)
The Ordered Task message specifies that the task be placed in the drive's task queue for execution in the
order received, with respect to other commands with Ordered Task messages, except for tasks received with
a Head of Queue message, which are placed at the head of the task set queue.
• Simple Task (20h)
The Simple Task message specifies that the task be placed in the drive's task set queue for execution. The
order of execution can be arranged by the drive in accordance with a performance optimization algorithm.
The Simple Task Tag message is also sent by the target when reconnecting to the initiator.
• ACA Message (24h)
Auto Contingent Allegiance
Restore Pointers (03h)
The Restore Pointers message is sent from a target to direct the initiator to restore the most recently saved
pointers (for the current task) to the active state. Pointers to the command, data, and status locations for the
nexus shall be restored to the active pointers. Command and status pointers shall be restored to the beginning
of the present command and status areas. The data pointer shall be restored to the value at the beginning of
the data area in the absence of a Save Data Pointer message or to the value at the point where the last Save
Data Pointer message occurred for that task.
Save Data Pointer (02h)
The Save Data Pointer message is sent from a target to direct the initiator to save a copy of the present active
data pointer for the current task. (See Section 3.4 for a definition of pointers.)
Synchronous Data Transfer Request (01h)
See Paragraph 3.5.3.2 on Extended Message.
33