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1.6 Transport layer
C141-C013 81
If necessary, fill bytes are placed after the INFORMATION UNIT field so that the
CRC field is aligned on a four-byte boundary. The number of the fill bytes is
specified by the NUMBER OF FILL BYTES field. If the transferred bytes in the
last DATA frame are not aligned on a four byte boundary, this field is set to the
number of the extra bytes (4 - the remainder of (the number of transferred bytes/4)
bytes).
The CRC field contains a CRC value that is computed over the entire SSP frame
prior to the CRC field including the fill bytes (i.e., all data dwords between the
SOF and EOF).
Drives ignore the Reserved fields.
1.6.2 Information units
1.6.2.1 COMMAND information unit
Table 1.34 defines the command IU. The COMMAND frame is sent by an SSP
INIT port to request that a command be processed by the device server in a logical
unit.
Table 1.34 COMMAND information unit
Bit
Byte
7 6 5 4 3 2 1 0
0 (MSB)
7
LOGICAL UNIT NUMBER
(LSB)
8 Reserved
9
ENABLE
FIRST
BURST
Reserved TASK ATTRIBUTE
10 Reserved
11
ADDITIONAL CDB LENGTH
(n dwords)
Reserved
12 (MSB)
27
CDB
(LSB)
28
27+ n x 4
ADDITIONAL CDB BYTES
The LOGICAL UNIT NUMBER field contains the address of the logical unit.
An ENABLE FIRST BURST bit set to "1" specifies that the first burst data item
is transferred as defined by the FIRST BURST SIZE field in the Disconnect-
Reconnect mode page. However, drives do not support this bit. Therefore, a
drive ignores the FIRST BURST SIZE field of the Disconnect-Reconnect mode
page.
Table 1.35 contains the definitions of the TASK ATTRIBUTE field. However,
drives do not support ACA in Table 1.35. Moreover, when a reserved TASK