Quantum SDLC 2.7, Справочное руководство

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Scalar DLC Reference Guide 289
SCSI Message System
The SCSI message system (Message In/Message Out) allows communication between an initiator and a
target for the purpose of physical path management.
Transfer The library supports asynchronous data transfer phases with differential and single
ended communications. Odd parity is generated during all information transfer phases
from the library. Parity is checked during all information transfer phases to the library.
Parity checking can be disabled.
Information Transfer phases include:
• The Message In/Message Out phases manage the physical path between the host
initiator and target destination. Message In is a message to the host initiator, Message
Out is a message to the target destination.
• Command Out phase is a command from the host initiator to the target destination.
• Data In/Data Out phase is either data sent from the target to the host initiator (Data
In) or data sent from the host initiator to the target destination (Data Out).
• Status In is a target status byte response to a host-initiated command.
Message Code Description Direction
COMMAND
COMPLETE 00h The COMMAND COMPLETE message is
sent from a target to an initiator to indicate that
the execution of a command is complete and
valid status has been sent to the initiator. In
SAVE DATA
POINTERS 02h The SAVE DATA POINTERS message is
issued before every disconnect message
following a Data In or Data Out phase. The
message is not sent when disconnecting after
a Command Descriptor Block (CDB) that did
not transfer data. In
RESTORE
POINTERS 03h The RESTORE POINTERS message is sent
from a target to direct the initiator to continue
sending data. In
DISCONNECT 04h The DISCONNECT message is sent by a
target to inform an initiator that the present
data transfer will be suspended. The target
will reselect the initiator at a later time to
continue the current operation. In
INITIATOR
DETECTED ERROR 05h The INITIATOR DETECTED ERROR
message is sent from an initiator to inform a
target that an error has occurred. This allows
the target to retry the operation. Out
ABORT 06h The ABORT message is sent from the initiator
to the target to clear the current or pending
operation. The target goes directly to the BUS
FREE phase after successful receipt of this
message. Out
Phase Description