1.6 Transport layer

If any additional XFER_RDY frames are required, the REQUESTED OFFSET field must be set to the value of the REQUESTED OFFSET in the previous XFER_RDY frame plus the value of the WRITE DATA LENGTH field in the previous XFER_RDY frame.

The WRITE DATA LENGTH field contains the number of bytes of write data the SSP INIT port will send to the logical unit from the application client buffer starting at the requested offset. The SSP TARG port sets the WRITE DATA LENGTH field to a value greater than or equal to 00000001h.

If an SSP TARG port sends a XFER_RDY frame containing a WRITE DATA LENGTH field that is not divisible by four, the SSP TARG port must not send any subsequent XFER_RDY frames for that command (i.e., only the last XFER_RDY for a command may request a non-dword multiple write data length).

When the drive sends a XFER_RDY 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

Always set to zero.

TAG field

The tag value of the COMMAND frame is set.

TARGET PORT TRANSFER TAG field The drive sets a value between 0 and 7.

DATA OFFSET field

Always set to zero.

REQUESTED OFFSET field

The first XFER_RDY frame for a command is always set to zero. If multiple XFER_RDY frames are to be sent for a single command, the value set in the field of the second XFER_RDY is increased by the value in the WRITE DATA LENGTH field of the first XFER_RDY frame. However, when transferring multiple XFER_RDY frames for a single command, the drive does not send the additional XFER_RDY frame until it receives the data requested with the first XFER_RDY frame. The value of the REQUESTED OFFSET field is divisible by four.

Table 1.39 An example of requested offset

XFER_RDY frame

REQUESTED OFFSET

WRITE DATA

C141-C013

87

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Fujitsu MBC2073RC, MBC2036RC, MBA3300RC, MBA3147RC, MBA3073RC An example of requested offset, Requested Offset Write Data