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1.6 Transport layer
C141-C013 91
• DATA OFFSET field
The DATA OFFSET field is used to check whether frames are being
transferred in the correct order. When the drive receives a frame with an
offset value that the drive does not expect, the drive sends the ACK primitive
and CREDIT_BLOCKED primitive, and discards the DATA frame. At this
time, after temporarily closing the connection, the drive re-opens a
connection and sends the SENSE DATA for DATA OFFSET ERROR.
• Received data length
When a data item with a data length exceeding the value specified in the
WRITE DATA LENGTH field of the XFER_RDY frame is received, the
drive sends the ACK primitive and CREDIT_BLOCKED primitive, and
discards the DATA frame. At this time, after temporarily closing the
connection, the drive re-opens a connection and sends the SENSE DATA for
TOO MUCH WRITE DATA.
Meanwhile, when a drive sends a read DATA frame, the following values are
set:
• HASHED DESTINATION SAS ADDRESS field
The hashed SAS address of the COMMAND frame is set.
• HASHED SOURCE SAS ADDRESS field
The hashed SAS address of the drive is set.
• NUMBER OF FILL BYTES field
If the transferred bytes in the last DATA frame for the command are not
aligned on a four byte boundary, the number of the extra bytes (4 - the
remainder of [the number of all transferred bytes/4] bytes) is set in this field.
• TAG field
The tag value of the COMMAND frame is set.
• TARGET PORT TRANSFER TAG field
Set to 0xFFFF by the drive.
• DATA OFFSET field
For the first DATA frame of the command, this field is set to zero. For the
second DATA frame, the DATA OFFSET field is increased by the number of
the transferred bytes of the first DATA frame.
• Number of transferred bytes
When the number of bytes to be transferred is greater than or equal to 1024
bytes, this field is set to 1024. When the number of bytes to be transferred is
less than 1024 bytes, this field is set to that number of bytes.