Quantum ATL PowerStor L200 Series, User Manual

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Chapter 4 SCSI Interface
SCSI Message System
60 ATL PowerStor L200 Series Library User’s Guide
Message Parity Error
(09h)
4
This message is sent from the initiator to the target to indicate that one
or more bytes in the last message it received had a parity error.
To indicate that it intends to send the message, the initiator sets the
ATN signal before it releases ACK 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 conditions, it proceeds directly
to the
BUS FREE
state by releasing the BSY signal, signifying a
catastrophic error.
The target's response to this message is to switch to the
MESSAGE IN
phase and re-send (from the beginning) all the bytes of the message,
that generated the original
MESSAGE PARITY ERROR
message.
Message Reject (07h)
4
This message is sent from the initiator or target to indicate that the last
message received was inappropriate or has not been implemented.
To indicate its intentions of sending this message, the initiator asserts
the ATN signal before it releases ACK for the REQ/ACK handshake of
the message that is to be rejected.
MESSAGE REJECT
is issued in response to any messages the library
considers to be illegal or not supported. When sending to the initiator,
the tape device will do so before requesting any additional message
bytes.
No-Op (No Operation)
(08h)
4
If a target requests a message, the initiator sends
NO-OP
if it does not
currently have any other valid message to send. The message is
accepted when the library is acting as a target, and may be sent when it
is an initiator. If
NO-OP
is received during a selection, the library
proceeds to the
COMMAND
phase (provided ATN does not continue
being asserted). The
NO-OP
message is ignored by the library.
Restore Pointers (03h)
4
This message is sent from a target to direct the initiator to restore the
most recently saved pointers (for the currently attached logical unit).
Pointers to the command, data, and status locations for the logical unit
are restored to the active pointers. Command and Status pointers are
restored to the beginning of the present Command and Status areas.
The Data pointer is 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 last
SAVE DATA POINTER
message that occurred for that
logical unit.
When the
RESTORE POINTERS
message is received as a target, the
target switches to the message in phase and returns
MESSAGE
REJECT
.