Scsi-2 Message Definitions; Command Complete Message (00H); Disconnect Message (04H); Initiator Detected Error Message (05H) - Spectra Logic Spectra 10000 User Manual

10kdev_.book Page 34 Friday, March 12, 1999 9:44 AM

SCSI-2 Message Definitions

Command Complete Message (00h) The Command Complete message is sent from the
library to an initiator, indicating that the execution of an I/O process has been completed
and that a valid status has been sent to the initiator. After successfully sending this
message, the command process is finished and the library goes to the Bus Free phase.
Disconnect Message (04h) The Disconnect message is sent from the library to an initiator
indicating that a pause in present I/O connection is needed. The library disconnects from
the SCSI bus by releasing the BSY signal. The Disconnect implies that a later Reconnect
will be required in order to complete the interrupted I/O process. The Disconnect
message does not cause the initiator to save the data pointers. After successfully sending
the Disconnect message, the library goes to the Bus Free phase.
Initiator Detected Error Message (05h) The Initiator Detected Error message is sent from
an initiator to the library to signal that the initiator has detected an error during an I/O
process. This does not preclude the target from retrying the operation. The cause of the
Initiator Detected Error may either be related to previous activities on the SCSI bus, or
a failure internal to the initiator (potentially unrelated to any previous SCSI bus activity).
Although data pointer integrity is not assured, a Restore Pointers message or a Disconnect
followed by a Reconnect causes the pointers to be restored to their defined prior state.
Abort Message (06h) The Abort message is sent from an initiator to the library to clear the
present process. Upon receipt of the Abort message, the library goes to the Bus Free phase
and terminates command execution.
Message Reject (07h) Message Reject is sent from an initiator to the library to indicate
that the last message received was inappropriate, has not been implemented, or cannot be
honored at this time.
No Operation Message (08h) In response to the library's request for a message, the No
Operation message is returned from an initiator when there is no valid message to be sent.
Message Parity Error Message (09h) The Message Parity Error is sent from the initiator to
the library to indicate that one or more bytes in the last message received had a parity
error.
Bus Device Reset Message (0Ch) The Bus Device Reset message is sent from an initiator to
a target to clear all I/O processes on that SCSI device. This message forces a "soft" reset
condition to the library. The library releases the SCSI Bus and creates a Unit Attention
for all initiators. This "soft" reset causes the library to perform a reset of all SCSI
hardware. During this SCSI hardware reset, the library performs an Initialize Element
Status, therefore the library's inventory will be accurate once this command is completed.
Identify Message (80h-FFh) The Identify message is sent by either the initiator or the
library to establish the physical transfer parameters between the two SCSI devices.
Chapter 3