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C141-E124-01EN1 - 16
b. If disconnecting after the final data transfer is completed
In the case of a disconnect after transfer of all the data necessary for execution of a command
has been completed normally, (example: a WRITE command), the IDD sends a
DISCONNECT message after sending the SAVE DATA POINTER message.
After that, the IDD executes reconnection processing and enters the STATUS phase
immediately and reports the status byte without requesting a data transfer.
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