Message Parity Error; Message Reject; Modify Data Pointer; No Operation - Seagate SCSI Interface Product Manual

32
Message Parity Error (09h)
The Message Parity Error message is sent from the initiator to the target to indicate that the last message byte
it received had a parity error.
In order to indicate its intentions of sending this message, the initiator shall assert the ATN signal prior to its
release of the ACK signal for the REQ/ACK handshake of the message that has the parity error. This provides
an interlock so that the target can determine which message has the parity error. If the target receives this
message under any other circumstance, it shall signal a catastrophic error condition by releasing the BSY sig-
nal without any further information transfer attempt (see Section 3.1.1).
Message Reject (07h)
The Message Reject message is sent from either the initiator or target to indicate that the last message byte it
received was inappropriate or has not been implemented.
In order to indicate its intentions of sending this message, the initiator shall assert the ATN signal prior to its
release of the ACK signal for the REQ/ACK handshake of the message byte that is to be rejected. If the target
receives this message under any other circumstance, it shall reject this message.
When a target sends this message, it shall change to Message In phase and send this message prior to
requesting additional message bytes from the initiator. This provides an interlock so that the initiator can deter-
mine which message byte is rejected.
Note. After a target sends a Message Reject message and if the ATN signal is still asserted, then it returns to
the Message Out phase. The subsequent Message Out phase begins with the first byte of a message,
not the middle of the previous message.
Modify Data Pointer (01h)
See Paragraph 3.5.3.2, Extended Message.
No Operation (08h)
The No Operation message is sent from an initiator in response to a target's request for a message when the
initiator does not currently have any other valid message to send.
For example, if the target does not respond to the attention condition until a later phase and at that time the
original message is no longer valid the initiator may send the No Operation message when the target enters
the Message Out phase.
Task Attribute messages (0Ah, 0Bh, 20h, 21h, 22h or 24h)
When one or more initiators have multiple I/O processes (called tasks) to be queued by a target, each task
must have a task tag associated with it. The task tag is specified in a Task Attribute message that must accom-
pany the initiation of each such task. See also Section 4.7.2, "Task Management."
Table 5. Task Attribute message format
Bit 7
Byte
0
1
Table 5 defines the format for the queue tag messages. Those drives that implement tagged task queuing and
use the Task Attribute messages Head of Queue Task Tag, Ordered Task Set Tag, and Simple Task Tag indi-
cate so in the individual drive's Product Manual, Volume 1.
The Task Attribute messages are used to specify an identifier, called a task tag, for a task that establishes the
I L Q nexus. The task tag field is an 8-bit unsigned integer assigned by the initiator during an initial connection.
The task tag for every task for each I T L nexus should be unique. If the drive receives a task tag identical to
one that is currently in use for the I T L nexus, the drive shall abort all tasks for the initiator and shall return
6 5
SCSI Interface Product Manual, Rev. J
4 3
Message Code
Tag (00h-FFh)
2 1 0