Dell PowerVault TL4000 SCSI Reference Guide - Page 102

Pointers, Restore, Disconnect, Initiator, Detected, Error, Abort, Message, Reject

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The Wide Data Transfer Request message is used to negotiate the width of the data path for the data transfers between the media changer and the initiator. The width applies to data phases only. The media changer does not support wide data transfers. When it receives a WDTR message from the initiator, it returns a WDTR message with a transfer width exponent of 0 (8-bit transfer width). The successful exchange of WDTR message implies an agreement to an 8-bit data transfer width. Bit 7 6 5 4 3 2 1 0 Byte 0 Extended Message (01h) 1 Extended Message Length (02h) 2 Extended Message Code (03h) 3 Transfer Width Exponent The Transfer Width field determines the width of the data path for data transfers. The media changer will return 00h for this field. This indicates that the media changer supports an 8-bit data transfer width only. Save Data Pointers 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 that did not transfer data. Restore Pointers The media changer sends the RESTORE POINTERS message to direct the initiator to copy the most recently saved command, data and status pointers of the I/0 process to the corresponding active pointers. The command and status pointers are restored to the value at the beginning of the data area. The media changer sends the Restore Pointers message after a detecting a parity error during the command phase or data out phase. After the media changer successfully sends the Restore Pointers message to the initiator, the media changer restarts the command, data in, data out, or status phase from the beginning. Disconnect 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. Initiator Detected Error The INITIATOR DETECTED ERROR message is sent from an initiator to inform a target that an error occurred. This allows the target to retry the operation. Abort The ABORT message terminates the current I/O process. The target goes directly to the BUS FREE phase after receipt of this message. Message Reject The MESSAGE REJECT message is sent from the initiator or target to indicate that the last message received was inappropriate or not implemented. 4-2 TL2000 and TL4000 SCSI Reference

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The
Wide
Data
Transfer
Request
message
is
used
to
negotiate
the
width
of
the
data
path
for
the
data
transfers
between
the
media
changer
and
the
initiator.
The
width
applies
to
data
phases
only.
The
media
changer
does
not
support
wide
data
transfers.
When
it
receives
a
WDTR
message
from
the
initiator,
it
returns
a
WDTR
message
with
a
transfer
width
exponent
of
0
(8-bit
transfer
width).
The
successful
exchange
of
WDTR
message
implies
an
agreement
to
an
8-bit
data
transfer
width.
Bit
7
6
5
4
3
2
1
0
Byte
0
Extended
Message
(01h)
1
Extended
Message
Length
(02h)
2
Extended
Message
Code
(03h)
3
Transfer
Width
Exponent
The
Transfer
Width
field
determines
the
width
of
the
data
path
for
data
transfers.
The
media
changer
will
return
00h
for
this
field.
This
indicates
that
the
media
changer
supports
an
8-bit
data
transfer
width
only.
Save
Data
Pointers
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
that
did
not
transfer
data.
Restore
Pointers
The
media
changer
sends
the
RESTORE
POINTERS
message
to
direct
the
initiator
to
copy
the
most
recently
saved
command,
data
and
status
pointers
of
the
I/0
process
to
the
corresponding
active
pointers.
The
command
and
status
pointers
are
restored
to
the
value
at
the
beginning
of
the
data
area.
The
media
changer
sends
the
Restore
Pointers
message
after
a
detecting
a
parity
error
during
the
command
phase
or
data
out
phase.
After
the
media
changer
successfully
sends
the
Restore
Pointers
message
to
the
initiator,
the
media
changer
restarts
the
command,
data
in,
data
out,
or
status
phase
from
the
beginning.
Disconnect
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.
Initiator
Detected
Error
The
INITIATOR
DETECTED
ERROR
message
is
sent
from
an
initiator
to
inform
a
target
that
an
error
occurred.
This
allows
the
target
to
retry
the
operation.
Abort
The
ABORT
message
terminates
the
current
I/O
process.
The
target
goes
directly
to
the
BUS
FREE
phase
after
receipt
of
this
message.
Message
Reject
The
MESSAGE
REJECT
message
is
sent
from
the
initiator
or
target
to
indicate
that
the
last
message
received
was
inappropriate
or
not
implemented.
4-2
TL2000
and
TL4000
SCSI
Reference