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1.7 Command Processing Exceptions
C141-E167 1 - 23
1) If a command is issued to the logical unit in the sense data hold state by the INIT which is the
object of sense data holding.
– In the case of an untagged command
REQUEST SENSE command: The sense data held by the IDD are transferred to the INIT and
the sense hold state is released.
Other commands: The sense data hold state is released and the command is
executed normally if commands issued from the INIT are not
queued. If commands issued from the INIT are queued, the
commands are treated as overlapping commands.
– In the case of a tagged command
The BUSY status is reported and the sense data hold state is released.
2) If a command is issued to the logical unit in the sense data hold state from an INIT which is not
the object of sense data holding, the sense data hold state is not released and the command is
queued.
3) In the following cases, the sense data hold state is released and the sense data being held are lost.
– The RESET condition occurs on the SCSI bus.
– A TARGET RESET message is issued by any INIT.
– An ABORT TASK SET message is issued by an INIT for which sense data held for the logical
unit in the sense data hold state.
1.7 Command Processing Exceptions
1.7.1 Overlapping commands
If the following state occurs, the IDD recognizes that overlapping commands have been generated
and the command is terminated abnormally.
1) During the IDD is executing or queuing an untagged command, the INIT that issued that
command before the completion of the command execution issues either an untagged command
or a tagged command.
2) If the IDD is executing or queuing a tagged command, the INIT that issued that command before
the completion of the command execution issues another tagged command with the same tag
specified as the previous command or an untagged command.
Normally, completion of a command execution is at the point when the TARG notifies the INIT of
the TASK COMPLETE message. Execution of a command can also be terminated by the RESET
condition, a TARGET RESET message, CLEAR TASK SET message, ABORT TASK SET message
or ABORT TASK message.
The IDD abnormally terminates all the commands (commands being executed or queued) received
from an INIT which is overlapping commands and the command that generated the overlap condition
by the procedure described below.
1) If the command received form the INIT is being executed, the IDD stops execution of the
command. If the command is still in the queue and execution has not been started, the IDD clears
that command.