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Quantum DLT 7000 Tape System 4-11
4.2.12 NO OPERATION (08h)
If a target requests a message, the initiator sends a NO OPERATION message if
it does not currently have any other valid message to send. The message is
accepted when the drive is acting as a target and may be sent when it is an
initiator. If a NO OPERATION message is received during a selection, the drive
proceeds to the COMMAND phase (provided ATN does not continue as
asserted); the NO OPERATION message is ignored by the tape drive.
4.2.13 RESTORE POINTERS Message (03h)
The RESTORE POINTERS message is sent from the drive to the initiator to
direct the initiator to copy the most recently saved command, data, and status
pointers for the I/O process to the corresponding current pointers. The 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 point at which the last SAVE DATA POINTER message 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.
4.2.14 SAVE DATA POINTER Message (02h)
The SAVE DATA POINTER message is sent from the drive to direct the
initiator to copy the current data pointer to the saved data pointer for the
current I/O process.
When functioning as a target, the tape drive sends this message before a
disconnect during a data transfer. It does not send a SAVE DATA POINTER
message if it intends to move directly to STATUS phase. When received as a
target, it switches to message in phase and returns MESSAGE REJECT.
4.2.15 SYNCHRONOUS DATA TRANSFER REQUEST Message (01h)
This extended message allows the target and initiator to agree on the values of
the parameters relevant to synchronous transfers. The tape drive will not initiate
the Synchronous Data Transfer Request message; it relies on the initiator to do
so. The Synchronous Data Transfer Request command has the format shown in
Figure 4-4.