2 aca (auto contingent allegiance) – Seagate Ultra 320 User Manual
Page 117
Parallel SCSI Interface Product Manual, Rev. A
103
When a target does a physical reconnection to an initiator to continue a tagged task, the Simple Queue mes-
sage shall be sent following the Identify message to resume the I_T_L_Q nexus for the task. Only one
I_T_L_Q nexus may occur during a physical reconnection. If the Simple Tag message is not sent, then only an
I_T_L nexus occurs for the task (i.e., an untagged command).
If a target attempts to do a physical reconnection using an invalid tag, then the initiator should create an atten-
tion condition. After the corresponding MESSAGE OUT phase, the initiator shall respond with an Abort Task
message.
If a target does not implement tagged queuing and a queue tag message is received, the target shall switch to
a Message In phase with a MESSAGE REJECT message and accept the task as if it were untagged, provided
there are no outstanding untagged tasks from that initiator.
See Section 7.0 of this manual and the ANSI SCSI Architecture Model-2 standard for the task set management
rules.
Table 40:
Task attribute message codes
Key:
M = Mandatory support
O = Optional support
Q = Mandatory if tagged queuing is implemented
In = Target to initiator
Out = Initiator to target
Yes = Initiator shall clear the attention condition before last ACK of the MESSAGE OUT phase.
Not required = Initiator may or may not clear the attention condition before last ACK of the MESSAGE OUT
phase (see Section 5.1).
N/A = Not applicable
4.4.2
ACA (AUTO CONTINGENT ALLEGIANCE)
See Table 41 for the format of the ACA message.
Table 41:
ACA message format
The ACA message specifies that the task shall be placed in the task set as an ACA task. The rules used by the
task manager to handle ACA tasks within a task set are defined in Section 7.0 of this manual and the SCSI
Architecture Model-2 standard.
Code
Support
Message name
Direction
Clear attention
condition
IU Transfers
Disabled
IU Transfers Enabled
Iniator
Target
Initiator
Target
24h
O
O
N/A
N/A
ACA
Out
Not required
21h
Q
Q
N/A
N/A
Head of Queue
Out
Not required
22h
Q
Q
N/A
N/A
Ordered
Out
Not required
20h
Q
Q
N/A
N/A
Simple
In
Out
Not required
Bit
Byte
7
6
5
4
3
2
1
0
0
MESSAGE CODE (24h)
1
TAG (00h-FFh)