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SAS Interface
80 C141-C013
The TAG field contains a value that allows the SSP INIT port to establish a
context for commands and task management functions.
For COMMAND frames and TASK frames, the SSP INIT port shall set the TAG
field to a value that is unique for the I_T nexus established by the connection. An
SSP INIT port shall not reuse the same tag when transmitting COMMAND frames
or TASK frames to different LUNs in the same SSP TARG port. An SSP INIT port
may reuse a tag when transmitting frames to different SSP TARG ports. The TAG
field in a COMMAND frame contains the task tag defined in SAM-3. The TAG
field in a TASK frame does not correspond to a SAM-3 task tag, but corresponds to
an SAM-3 association. The tag space used in the TAG fields is shared across
COMMAND frames and TASK frames (e.g., if a tag is used for a COMMAND
frame, it is not also used for a concurrent TASK frame).
For DATA, XFER_RDY, and RESPONSE frames, the SSP TARG port shall set
the TAG field to the tag of the command or task management function to which
the frame pertains.
The TARGET PORT TRANSFER TAG field provides an optional method for an
SSP TARG port to establish the write data context when receiving a write DATA
frame (i.e., determine the command to which the write data corresponds).
SSP TARG ports may set the TARGET PORT TRANSFER TAG field to any
value when transmitting any SSP frame. SSP TARG ports that use this field
should set the TARGET PORT TRANSFER TAG field in every XFER_RDY
frame to a value that is unique for the L_Q portion of the I_T_L_Q nexus (i.e.,
that is unique for every XFER_RDY that is outstanding from the SSP TARG
port).
SSP INIT ports shall set the TARGET PORT TRANSFER TAG field as follows:
a) For each write DATA frame that is sent in response to an XFER_RDY frame,
the SSP INIT port shall set the TARGET PORT TRANSFER TAG field to
the value that was in the corresponding XFER_RDY frame;
b) For frames other than DATA frames, the SSP INIT port sets the TARGET
PORT TRANSFER TAG field to FFFFh. However, this setting is not
forcibly made.
Remarks: Drives do not support the FIRST BURST SIZE field of the
Disconnect-Reconnect mode page (page code 02h).
For DATA frames, the DATA OFFSET field is described later. For all other
frame types, the DATA OFFSET field shall be ignored.
The INFORMATION UNIT field contains the information unit, the format of
which is defined by the FRAME TYPE field. The maximum size of the
INFORMATION UNIT field is 1024 bytes, making the maximum size of the
frame 1052 bytes (1024 bytes of data + 24 bytes of header + 4 bytes of CRC).