Dell PowerVault TL4000 SCSI Reference Guide - Page 66

Buffer, Descriptor

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Bit 7 6 5 4 3 2 1 0 Byte 0 - n (data defined by previous Data Mode WRITE BUFFER command) Echo Mode In this mode, the library returns the same number of bytes of data as received in the prior Echo Mode WRITE BUFFER command from the same host. If a prior Echo Mode WRITE BUFFER command did not complete successfully the Echo Mode READ BUFFER command shall return Check Condition status. The sense key shall be set to ILLEGAL REQUEST and the sense data shall be set to COMMAND SEQUENCE ERROR. If the data in the Echo Buffer has been overwritten by another host the library shall return Check Condition status. The sense key shall be set to ILLEGAL REQUEST and the sense data shall be set to ECHO BUFFER OVERWRITTEN. The maximum length of the Echo Mode buffer is 256 bytes. Bit 7 6 5 4 3 2 1 0 Byte 0 - n (data defined by previous Echo Mode WRITE BUFFER command) Echo Buffer Descriptor Mode In this mode, the media changer returns the descriptor information for the Echo Buffer. The Buffer Offset field is reserved in this mode. The Buffer ID field is ignored in this mode. Next table specifies the Buffer Descriptor which is returned on a READ BUFFER command in Echo Buffer Descriptor Mode. Bit 7 6 5 4 3 2 1 0 Byte 0 Reserved EBOS 1 Reserved 2 Reserved (MSB) 3 Buffer Capacity (LSB) Field descriptions: EBOS: The Echo Buffer Overwritten Support bit is set. The library shall return ECHO_BUFFER_OVERWRITEN sense data when the buffer is overwritten by another initiator. Buffer Capacity: The Buffer Capacity field returns the maximum size of the Echo Buffer in bytes. The Echo Buffer can store up to 256 bytes. 3-52 TL2000 and TL4000 SCSI Reference

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Bit
7
6
5
4
3
2
1
0
Byte
0
-
n
(data
defined
by
previous
Data
Mode
WRITE
BUFFER
command)
Echo
Mode
In
this
mode,
the
library
returns
the
same
number
of
bytes
of
data
as
received
in
the
prior
Echo
Mode
WRITE
BUFFER
command
from
the
same
host.
If
a
prior
Echo
Mode
WRITE
BUFFER
command
did
not
complete
successfully
the
Echo
Mode
READ
BUFFER
command
shall
return
Check
Condition
status.
The
sense
key
shall
be
set
to
ILLEGAL
REQUEST
and
the
sense
data
shall
be
set
to
COMMAND
SEQUENCE
ERROR.
If
the
data
in
the
Echo
Buffer
has
been
overwritten
by
another
host
the
library
shall
return
Check
Condition
status.
The
sense
key
shall
be
set
to
ILLEGAL
REQUEST
and
the
sense
data
shall
be
set
to
ECHO
BUFFER
OVERWRITTEN.
The
maximum
length
of
the
Echo
Mode
buffer
is
256
bytes.
Bit
7
6
5
4
3
2
1
0
Byte
0
-
n
(data
defined
by
previous
Echo
Mode
WRITE
BUFFER
command)
Echo
Buffer
Descriptor
Mode
In
this
mode,
the
media
changer
returns
the
descriptor
information
for
the
Echo
Buffer.
The
Buffer
Offset
field
is
reserved
in
this
mode.
The
Buffer
ID
field
is
ignored
in
this
mode.
Next
table
specifies
the
Buffer
Descriptor
which
is
returned
on
a
READ
BUFFER
command
in
Echo
Buffer
Descriptor
Mode.
Bit
7
6
5
4
3
2
1
0
Byte
0
Reserved
EBOS
1
Reserved
2
Reserved
(MSB)
3
Buffer
Capacity
(LSB)
Field
descriptions:
EBOS:
The
Echo
Buffer
Overwritten
Support
bit
is
set.
The
library
shall
return
ECHO_BUFFER_OVERWRITEN
sense
data
when
the
buffer
is
overwritten
by
another
initiator.
Buffer
Capacity:
The
Buffer
Capacity
field
returns
the
maximum
size
of
the
Echo
Buffer
in
bytes.
The
Echo
Buffer
can
store
up
to
256
bytes.
3-52
TL2000
and
TL4000
SCSI
Reference