Quantum ATL PowerStor L200 Series, User Manual

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Chapter 4 SCSI Interface
General SCSI Bus Operation
54 ATL PowerStor L200 Series Library User’s Guide
Status Phase
4
The library enters the status phase just once per command, unless the
initiator requests a retry. The only exception is during error cases when
the device goes immediately to bus free, as defined in the SCSI-2
standard.
The library can return any of the following status bytes:
•
GOOD (00)
: This status indicates the library successfully
completed the command.
•
CHECK CONDITION (02)
: A contingent allegiance condition
occurred. The
REQUEST SENSE
command should be sent
following this status to determine the nature of the event.
•
BUSY (08)
: The target is busy. This status is returned whenever
the device is unable to accept a command from an otherwise
acceptable initiator. The initiator should reissue the command at a
later time.
•
INTERMEDIATE GOOD (10h)
: This status is returned instead of
GOOD
status for commands issued with the
LINK
bit set. Following
the return of this status, the library will proceed to the
COMMAND
phase for the transfer of the next linked command.
•
RESERVATION CONFLICT (18h)
: This status is returned by the
library whenever a SCSI device attempts to access the library when
it has been reserved for another initiator with a
RESERVE UNIT
command.
• COMMAND TERMINATED (22h)
: This is the status returned for a
command that was terminated by a
TERMINATE I/O PROCESS
message. This status also indicates that a contingent allegiance
condition has occurred.
The
Test Unit Ready
command is used to determine whether the
library would accept, for example, a
MOVE MEDIUM
or
POSITION
command without returning
CHECK CONDITION
status.
Bus Free
4
There are several situations when the device will go to
BUS FREE
unexpectedly, as defined in the SCSI-2 standard (see sections 4.1.1 and
4.3):
•
An internal hardware or firmware fault that makes it unsafe for the
device to continue operation without a full reset (similar to a
power-up reset).
•
ATN asserted or bus parity error detected during non-tape data
transfers.