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WDTR Response:
1) Non-zero transfer width
2) Transfer width equal to zero
3) MESSAGE REJECT message
Tandberg Data
6.3.1.
Wide Data Transfer Request
The Wide Data Transfer Request (WDTR) message exchange
establishes an agreement between the Initiator and the
Drive on the width of the data path to be used for DATA
phase transfers between the two devices. The agreement
applies to DATA IN and DATA OUT phases only. All other
information phases will use an eight-bit data path.
A WDTR message exchange is initiated by the Initiator
whenever a previously arranged transfer width agreement
may have become invalid, or whenever it is appropriate
to
negotiate
a
negotiation at every selection is not recommended, since
a significant performance impact is likely.
The agreement becomes invalid after a reset condition.
The Initiator sets its transfer width to the maximum
data path width it elects to accommodate. If the Drive
can also accommodate this transfer width, it returns the
same value in its WDTR message. If it requires a smaller
transfer width, it substitutes the smaller value in its
WDTR message. The successful completion of an exchange
of WDTR messages implies an agreement as follows:
Implied agreement:
Each device transmits and receives data with the specified transfer width.
Eight-bit data transfer
Eight-bit data transfer
If
the
initiator
required, it asserts the ATN signal and sends a WDTR
message
to
begin
successfully completing the MESSAGE OUT phase, the Drive
responds with the proper WDTR message. If an abnormal
condition
prevents
appropriate response, both devices shall go to eight-bit
data transfer mode for data transfers between the two
devices.
Following
Drive
agreement for wide data transfers is considered to be
negated
if
the
message out is either MESSAGE PARITY ERROR or MESSAGE
REJECT. In this case, both devices shall go to eight-bit
data transfer mode for data transfers between the two
devices. For the MESSAGE PARITY ERROR case, the implied
agreement shall be reinstated if a re-transmittal of the
second
of
the
accomplished. After a specific number of retry attempts,
if the Drive receives a MESSAGE PARITY ERROR message, it
will
terminate
shall
go
to
eight-bit
transfers between the two devices. The number of retry
attempts is specified in the Bus Parity Error Retries
field
in
the
Miscellaneous
command.
Please
details.
The implied transfer width agreement shall remain in
effect until a TARGET RESET message is received, until a
hard
reset
condition
6-6
Tandberg SLR Product Line SCSI Functional Specifications
new
transfer
recognizes
the
negotiating
the
Drive
response
(1)
initiator
asserts
pair
of
messages
the
retry
activity,
data
transfer
Page
refer
to
section
occurs,
or
Message System
width
agreement.
that
negotiation
process.
from
returning
above,
the
implied
ATN
and
the
is
successfully
and
both
devices
mode
for
of
the
Mode
14.3.9
for
further
until
the
Initiator
Re-
is
After
an
first
data
Select
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