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The parameters that can be changed by modifying the operating definition of a logical unit include the vendor
identification, the device type, the device model, the SCSI compliance level, the SCSI specification level, the
command set, and other parameters. The low-level hardware parameters including signal timing and parity def-
initions cannot be changed by modifying the operating definition. The present operating definition of a logical
unit with respect to a SCSI initiator port can be determined at any time by execution of an INQUIRY command.
In some vendor-specific cases, it may also be necessary to perform other commands including Mode Sense
and READ CAPACITY.
The more recent Seagate drives do not support the Change Operating Definition command (see individual
drive's Product Manual, Volume 1).
Each logical unit begins at a particular operating definition. If the logical unit supports the CHANGE DEFINI-
TION command, the present operating definition can be changed to any other operating definition supported
by the logical unit. The actual details of the operating definition of a logical unit are vendor-specific. If the oper-
ating definition is changed to one that does not include the CHANGE DEFINITION command, the target contin-
ues to accept the CHANGE DEFINITION command.
If an error occurs during execution of a CHANGE DEFINITION command, the original operating definition
remains in effect after the command is executed. The new operating definition becomes active only after suc-
cessful execution of the CHANGE DEFINITION command.
Since new operating definitions may preclude the execution of tasks that are already in progress, the target
may disconnect to allow completion of any tasks that are in progress. Operating definition changes that may
cause conflicts with the normal operation from other initiators shall be indicated to those initiators by generating
a Unit Attention condition for each other initiator. The additional sense code shall be set to Changed Operating
Definition.
a SCSI initiator port may request a list of the operating definitions that the target supports and descriptive text
for each operating definition using the INQUIRY command.
7.10
Incorrect initiator connection
An incorrect initiator connection occurs on a reconnection if:
a. a SCSI initiator port attempts to reconnect to a task, and
b. a soft reset condition has not occurred, and
c. the initiator does not send an Abort, Abort Tag, Bus Device Reset, Clear Task Set, Continue Task, or Termi-
nate Task message during the same MESSAGE OUT phase as the IDENTIFY message.
An incorrect initiator connection also occurs on an initial connection when a SCSI initiator port:
a. attempts to establish an I T L Q nexus when an I T L nexus already exists from a previous connection, or
b. attempts to establish an I T L nexus when an I T L Q nexus already exists unless there is a contingent alle-
giance or extended contingent allegiance condition present for the logical unit or target routine.
a SCSI target port that detects an incorrect initiator connection shall abort all tasks for the initiator on the logi-
cal unit or target routine and shall return CHECK CONDITION status. The sense key shall be set to Aborted
Command and the additional sense code shall be set to Overlapped Commands Attempted.
An incorrect initiator connection may be indicative of a serious error and if not detected could result in a task
operating with a wrong set of pointers. This is considered a catastrophic failure on the part of the initiator.
Therefore, host-specific error recovery procedures may be required to guarantee the data integrity on the
medium. The target may return additional sense data to aid in this error recovery procedure. Also, some tar-
gets may not detect an incorrect initiator connection until after the command descriptor block has been
received.
SCSI Interface Product Manual, Rev. B
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