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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) If the IDD is executing an untagged command, or an untagged command is in the queue,
and the initiator that issued that command issues either an untagged command or a tagged
command before execution of the previous command is completed.
2) If the IDD is executing a tagged command, or a tagged command is in the queue, and the
initiator that issued that command issues another tagged command with the same tag
specified as the previous command before execution of that command is completed.
Normally, execution of a command is completed at the point when the TARG notifies the
INIT of the COMMAND COMPLETE message. Execution of a command can also be
terminated by the RESET condition, a BUS DEVICE RESET message, CLEAR QUEUE
message, ABORT message or ABORT TAG message.
The IDD abnormally terminates all the commands (commands being executed or in the queue)
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 halts execution of the
command. If the command is still in the queue and execution has not been started, the
IDD clears that command.
2) The IDD reports a CHECK CONDITION status for a command that generates an overlap.
At this time, the sense data generated by the IDD indicates ABORTED COMMAND
[=B]/Overlapped commands attempted [=4e-00], or Tagged Overlapped [=4D-nn] (nn: tag
No.).
Note
1)
In order for the INIT to halt processing of a command during a disconnect, it is
permitted to send an ABORT TAG message, ABORT message, CLEAR QUEUE
message or BUS DEVICE RESET message, specifying the logical unit (see item
1.7.6).
2)
Specification of overlapping commands applies without dependence upon the type of
command that is issued second. For example, even if the command issued second is
the INQUIRY or REQUEST SENSE command, the IDD reports the CHECK
CONDITION status and terminates both the first command and the second command
abnormally.