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1.6.2.4
DATA information unit
Table 1.40 defines the data IU. The DATA frame is sent by an SSP INIT port to
deliver write data (i.e., a write DATA frame) and is sent by an SSP TARG port to
deliver read data (i.e., a read DATA frame). The maximum size of the data IU is
the maximum size of any IU in an SSP frame. The minimum size of the data IU
is one byte.
Bit
Byte
0
n-1
An SSP INIT port shall only transmit a write DATA frame:
a) in response to an XFER_RDY frame; or
b) after transmitting a COMMAND frame if the ENABLE FIRST BURST field
in the COMMAND frame was set to one and the FIRST BURST SIZE field
in the Disconnect-Reconnect mode page is not zero.
However, since drives do not support the FIRST BURST SIZE field, a drive can
receive data only when it requests data with XFER_RDY frames.
If the value in the MAXIMUM BURST SIZE field on the Disconnect-Reconnect
mode page is not zero, the maximum amount of data that is transferred at one
time by an SSP TARG port per I_T_L_Q nexus is limited by the value in the
MAXIMUM BURST SIZE field.
Drives do not support the MAXIMUM BURST SIZE field. However, the
maximum data amount a drive can request with a single XFER_RDY frame is
limited to 64 Kbytes.
An SSP TARG port shall set the NUMBER OF FILL BYTES field to zero in the
frame header in all read DATA frames for a command except the last read DATA
frame for that command. The SSP TARG port may set the NUMBER OF FILL
BYTES field to a non-zero value in the last read DATA frame for a command
(i.e., only the last read DATA frame for a command may contain data with a
length that is not a multiple of four).
An SSP INIT port may set the NUMBER OF FILL BYTES field to a non-zero
value contained in the last DATA frame that is sent as a response to an
XFER_RDY frame. In this case, the SSP INIT port must set zeros in the
NUMBER OF FILL BYTES fields in the frame headers of all the other data
frames to be sent.
C141-C009
Table 1.40 DATA information unit
7
6
5
DATA (1byte to 1024bytes)
4
3
2
1.6 Transport layer
1
0
1-69
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