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CDU-541 CD-ROM DRIVE SCSI INTERFACE MANUAL
4 .
2.
7. Flag and
Link
Bi
ts
The link bit set to one indicates that the initiator requests a link to the
next command upon successful completion of the current command.
If the link
bit is one, the controller will return INTERMEDIATE status upon successful
termination of the command.
The message sent depends on the flag bit.
The link bit set to zero indicates that the initiator does not want the
commands linked.
If the link bit is set to zero, the flag bit shall be set to
zero .
If the link bit is set to one and the flag bit is set to zero, the
controller will send LINKED COMMAND COMPLETE message if the current command
completes successfully.
If the link bit is set to one and the flag bit is set to one, the controller
will send LINKED COMMAND COMPLETE(WITH
FLAG)
message if the current command
completes successfully.
4.3. Command Processing
Upon normal command completion (successful or unsuccessful), the controller
returns a status byte to the initiator.
Since most error and exception
conditions cannot be adequately described with a single status byte, one
status code, CHECK CONDITION,
~dicates
that additional information is
available.
The initiator may issue a REQUEST SENSE command to retrieve this
additional information.
An
initiator should never send a second command to a logical unit until the
command in progress is terminated.
The command is normally terminated with a
COMMAND COMPLETE message, but termination may result because of other events·
such as the RESET condition.
If the controller receives a selection from an initiator that has a command
in progress (i.e. the controller has disconnected) the controller will abort
the first command and not perform the second command.
A CHECK CONDITION
status is returned.
The sense key is set to ABORTED COMMAND, and the
additional sense code is set to OVERLAPPED COMMANDS ATTEMPTED.
The occurrence of an initiator sending
a
second command to a logical unit
with a command in progress by the same initiator is considered a catastrophic
failure from the controller's viewpoint.
4-5
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