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Command Processing
1 - 14 C141-E167
Note:
In disconnect processing in this case, transfer of all the data accompanying execution of the
command is complete and there is actually no necessity for the SAVE DATA POINTER
message.
However, by issuing the SAVE DATA POINTER message, processing time increases due to
the message transfer, but as a result of the pointer restore operation that is executed
internally by the INIT during reconnection processing for the status report, the current data
pointer can reflect the final results of the data transfer.
(5) Disconnect processing exceptions
When the previously mentioned disconnect processing is executed, if the ATTENTION condition is
generated for the DISCONNECT message sent by the IDD and the INIT returns the MESSAGE REJECT
message, the IDD executes the command with the connections to the SCSI bus remaining as is, without
executing disconnect processing. Cases of disconnect processing in which a pointer operation is necessary
and the SAVE DATA POINTER message is rejected are the same.
(6) Reconnection processing procedure
The reconnection processing procedure is as shown below.
1) The IDD executes the ARBITRATION phase at the point when processing on the SCSI bus is
necessary and gets the SCSI bus control right, then reconnects with the INIT in the
RESELECTION phase.
2) After that, the IDD sends the IDENTIFY message to the INIT and notifies it of the logical unit
number (LUN) necessary for reconnection processing. If a tagged queuing command is executed,
the IDD sends the SIMPLE message to inform the INIT of the tag ID. The INIT reads the Saved
pointer (command, data and status) corresponding to the LUN specified at this time and restores
it to the current pointer.
Note:
1) If there is no response from the INIT within the specified time (default: 250 ms) in the
RESELECTION phase, the IDD performs timeout processing, then enters the BUS
FREE phase. In this case, after waiting 200 ms or longer, the IDD executes the
predetermined number of retries (re-executing the RESELECTION phase). However,
if it still cannot reconnect with the INIT after that, the IDD clears the command
necessary for reconnection processing and generates sense data indicating ABORTED
COMMAND[=B]/Select /Reselect failure[=45-00].
2) If the INIT rejects the IDENTIFY message, or if it rejects the SIMPLE message when
executing a tagged queuing command, the IDD clears the command that was being
executed during reconnection processing and enters the BUS FREE phase. In this case,
the IDD generates sense data indicating ABORTED COMMAND[=B]/Message
error[=43-00].