SCSI Message Support
The
disk drive supports messages received from
the
Initiator
in
the
following manner:
• Multiple
byte
message
out
phases are allowed.
• Any message out may be prefixed with an optional Identify byte.
• An optional number
of
No-Op message bytes
may
be embedded in
the
message
out
received
by
the
disk drive prior
to
the
final message byte.
• Only one message type
(other
than
the
Identify prefix and
the
optional N o-Op bytes) will
be accepted per message
out
phase.
If
more
than
one type is received,
the
message will
be
treated
as an illegal message.
• A maximum of 16-message out bytes will be accepted by
the
disk drive.
if
the
ATN line is
still set after
16
bytes have been received, the disk drive will
treat
this as an illegal message
type, except
that
the
disk drive will always
terminate
in a Bus Free
state.
The
following message types are supported:
Message Parity
Error
Initiator Detected
Error
Abort
Reset
No-Op
Message Reject
DRAFT
1/18/93 09:58
If
either of these messages
is
received from the Initiator, the disk drive
will abort the command in process
and
set the sense key to Aborted
Command
with the sense code set to Initiator Detected Error.
If
a
valid
LUN
has been received in an Identify or CDB, and a
status
phase
has
not
yet begun, then the command will be terminated with a Check
Condition
status; otherwise the Target will go to the Bus Free state.
This message will cause the disk drive to
abort
the command in
process, clear the Initiator's status and go
to
the Bus Free state.
This message will cause the disk drive
to
abort the command in
process, reset to
Power On conditions for all Initiators, and go to the
Bus Free state.
This message will be treated
as
an illegal message type if
not
followed
by
some legal message byte, except when the No-Op message type
is
received immediately following a Re-select
attempt
by the Target. In
this case, the Target will
attempt
to
proceed with the interrupted
re-select phase.
If
a Message Reject message
is
received from
the
Initiator
it
will
normally be treated like an Illegal Message.
Only if the Target
is
in the
Message In phase and attempting
to
send one of the following messages
will
it
be treated differently.
Disconnect Message
In, Save
Data
Pointer
Message.ln~
The
Target
will not disconnect and will proceed with the command in process.
This
will
not
prevent the disk drive from
attempting
to
disconnect
from the Initiator
at
a later time.
Synchronous
Data
Transfer Message In.
The
Target will assume
that
an asynchronous transfer is expected. This will affect all later
data
transfer phases.
SCSI
Interface 4·7
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