Dell PowerVault TL4000 SCSI Reference Guide - Page 65

Descriptor

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The following structure specifies the Variables Setting page. A WRITE BUFFER command to this page is used to update the setting variables in NV-RAM. Bit 7 6 Byte 0 1 2 3 4 (MSB) ... 45 5 4 3 2 Reserved Additional Page Length (2Ch) Reserved Reserved Current Setting Variables (42 bytes) 1 0 (LSB) Note: For a description of the possible Setting Variables, see the table at the WRITE BUFFER command. Descriptor Mode In this mode, the media changer returns the Buffer Capacity of the specified Buffer ID in Data Mode. If a not supported Buffer ID is specified the media changer will return zero as Buffer Capacity. Next table specifies the Buffer Descriptor which is returned on a READ BUFFER command in Descriptor Mode. Bit 7 6 Byte 0 1 (MSB) ... 3 5 4 3 2 Offset Boundard (0) Buffer Capacity 1 0 (LSB) Field descriptions: Offset Boundary: The Offset Boundary field defines the byte alignment for the buffer. The media changer only supports byte alignment, so this value will be zero. Buffer Capacity: The Buffer Capacity field returns the size of the specified Buffer ID buffer in bytes. Note that this is the maximum size including the length byte. The Read Buffer command in Data Mode supports Buffer ID zero. Buffer ID zero can store up to 256 bytes. The returned Buffer Capacity for Buffer ID zero is 000100h. The uffer Capacity for all other Buffer ID values is set to 000000h. Data Mode In this mode, the library returns the information stored in the specified Buffer ID. This mode is used to test SCSI bus data integrity in conjunction with the WRITE BUFFER command. The Data Mode returns up to 256 bytes from the specified Buffer ID to the host. The value in the Buffer Offset field may not exceed the length of the specified Buffer ID. Only Buffer ID 00h is supported. Potential Buffer overruns are detected and the command is rejected. By means of a READ BUFFER command in Data Mode the host can retrieve the information sent by a WRITE BUFFER command in Data Mode. The returned number of bytes is defined by the value stored in the Allocation Length field of the READ BUFFER CDB. Chapter 3. Supported SCSI Commands 3-51

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The
following
structure
specifies
the
Variables
Setting
page.
A
WRITE
BUFFER
command
to
this
page
is
used
to
update
the
setting
variables
in
NV-RAM.
Bit
7
6
5
4
3
2
1
0
Byte
0
Reserved
1
Additional
Page
Length
(2Ch)
2
Reserved
3
Reserved
4
(MSB)
...
Current
Setting
Variables
(42
bytes)
45
(LSB)
Note:
For
a
description
of
the
possible
Setting
Variables,
see
the
table
at
the
WRITE
BUFFER
command.
Descriptor
Mode
In
this
mode,
the
media
changer
returns
the
Buffer
Capacity
of
the
specified
Buffer
ID
in
Data
Mode.
If
a
not
supported
Buffer
ID
is
specified
the
media
changer
will
return
zero
as
Buffer
Capacity.
Next
table
specifies
the
Buffer
Descriptor
which
is
returned
on
a
READ
BUFFER
command
in
Descriptor
Mode.
Bit
7
6
5
4
3
2
1
0
Byte
0
Offset
Boundard
(0)
1
(MSB)
...
Buffer
Capacity
3
(LSB)
Field
descriptions:
Offset
Boundary:
The
Offset
Boundary
field
defines
the
byte
alignment
for
the
buffer.
The
media
changer
only
supports
byte
alignment,
so
this
value
will
be
zero.
Buffer
Capacity:
The
Buffer
Capacity
field
returns
the
size
of
the
specified
Buffer
ID
buffer
in
bytes.
Note
that
this
is
the
maximum
size
including
the
length
byte.
The
Read
Buffer
command
in
Data
Mode
supports
Buffer
ID
zero.
Buffer
ID
zero
can
store
up
to
256
bytes.
The
returned
Buffer
Capacity
for
Buffer
ID
zero
is
000100h.
The
uffer
Capacity
for
all
other
Buffer
ID
values
is
set
to
000000h.
Data
Mode
In
this
mode,
the
library
returns
the
information
stored
in
the
specified
Buffer
ID.
This
mode
is
used
to
test
SCSI
bus
data
integrity
in
conjunction
with
the
WRITE
BUFFER
command.
The
Data
Mode
returns
up
to
256
bytes
from
the
specified
Buffer
ID
to
the
host.
The
value
in
the
Buffer
Offset
field
may
not
exceed
the
length
of
the
specified
Buffer
ID.
Only
Buffer
ID
00h
is
supported.
Potential
Buffer
overruns
are
detected
and
the
command
is
rejected.
By
means
of
a
READ
BUFFER
command
in
Data
Mode
the
host
can
retrieve
the
information
sent
by
a
WRITE
BUFFER
command
in
Data
Mode.
The
returned
number
of
bytes
is
defined
by
the
value
stored
in
the
Allocation
Length
field
of
the
READ
BUFFER
CDB.
Chapter
3.
Supported
SCSI
Commands
3-51