IBM DCAS-32160 - Ultrastar 2.1 GB Hard Drive, Технические характеристики

Страница: 185 / 232

9.1.6 DISCONNECT (04)
This message is sent from the file to inform an initiator that the present connection is going to be broken.
A later reconnect will be required in order to complete the current command. The disconnection is to free
the SCSI bus while the file performs a relatively long operation that does not require the bus. These mes-
sages are only sent if the initiator previously indicated (via the I D E N T I F Y message) the ability to accommo-
date disconnection and reconnection.
The DISCONNECT message may also be sent from the initiator to the file to disconnect from the SCSI
bus. The file does not support the DISCONNECT message from the initiator. And it always respond by
sending MESSAGE R E J E C T message to the initiator.
9.1.7 INITIATOR DETECTED ERROR (05)
This message is sent from an initiator to inform the file that an error has been detected that does not pre-
clude the file from retrying the previous C O M M A N D , D A T A and STATUS phase. The source of the error
may be either related to previous activities on the SCSI bus or may be internal to the initiator and unrelated
to any previous SCSI bus activity
If the initiator intends to send this message, the initiator must assert the A T N signal prior to its release of
ACK for the last byte transferred in the information phase that is to be retried. This provides an interlock
so the file can determine which information phase to retry.
After receiving this message, the file may retry the previous phase by sending a R E S T O R E P O I N T E R S
message to the initiator and then repeating the previous C O M M A N D , DATA, or STATUS phase.
9.1.8 ABORT (06)
This message is sent from the initiator to direct the file to clear the present operation for this initiator and
logical unit, including queued command(s). If a logical unit has been identified, then all pending data and
status for the issuing initiator and this logical unit will be cleared and the file will go to the BUS F R E E
phase. Pending data and status for other logical unit and initiators will not be cleared. If a logical unit has
not been identified, the file will go to the BUS F R E E phase without affecting an operation on any logical
unit for this initiator or any other initiator. In either case, no status or ending message will be sent to the
initiator for this operation.
It is not an error to send the A BO RT message to a logical unit that is not
currently performing an operation for the initiator.
Note: It is permissible for an initiator to select the file/LUN after the file has disconnected from the initi-
ator, for the purpose of sending an I D E N T I F Y message followed by an AB O R T message. This will abort
the command on the specified logical unit.
9.1.9 MESSAGE REJECT (07)
This message is sent from either the initiator or the file to indicate that the last message received was inap-
propriate or has not been implemented.
If the initiator intends to send this message, the initiator must assert the A T N signal prior to its release of
ACK for the R E Q / A C K handshake of the message byte that is to be rejected. This provides an interlock so
the file can determine which message is rejected.
If the file intends to send this message, the file will change to the MESSAGE IN phase and send the
MESSAGE R E J E C T message to the initiator prior to transferring any additional message bytes (or any
other information phase bytes) from the initiator regardless of A T N signal. This provides an interlock so the
SCSI MESSAGE SYSTEM
171