Other Important Design Notes - Xilinx RocketIO User Manual

Other Important Design Notes

ALIGN_COMMA_MSB is set to TRUE, the comma appears in RXDATA[15:8] for the 2-byte
primitives, and in either RXDATA[15:8] or RXDATA[31:24] for the 4-byte primitives. (See
"ALIGN_COMMA_MSB," page
In the case of a 4-byte primitive, the transceiver sets comma alignment with respect to its 2-byte
internal data path, but it does not constrain the comma to appear only in RXDATA[31:24]. Logic
must be designed in the FPGA fabric to handle comma alignment for the 32-bit primitives when
implementing certain protocols. (Note that FPGA logic is not required for 1-byte and 2-byte
configurations.)
One such protocol is Fibre Channel. Delimiters such as IDLES, SOF, and EOF are four bytes long,
and are assumed by the protocol logic to be aligned on a 32-bit boundary. The Fibre Channel IDLE
delimiter is four bytes long and is composed of characters K28.5, D21.4, D21.5, and D21.5. The
comma, K28.5, is transmitted in TXDATA[31:24], which the protocol logic expects to be received
in RXDATA[31:24].
Using
hexadecimal value 0xBC95B5B5 that represents the 32-bit RXDATA word. On the 32-bit
RXDATA interface, the received word is either 32-bit aligned or misaligned, as shown in
Table
Table 2-24: 32-bit RXDATA, Aligned versus Misaligned
When RXDATA is 32-bit aligned, the logic should pass RXDATA though to the protocol logic
without modification. A properly aligned data flow is shown in
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
Table B-1, page 133, and
2-24. In the table, "pp" indicates a byte from a previous word of data.
RXDATA
32-bit aligned
CHARISCOMMA
32-bit misaligned
CHARISCOMMA
TXDATA
BC95B5B5
RXDATA
BC95B5B5
ALIGNED_DATA
pppppppp
Figure 2-29: RXDATA Aligned Correctly
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68.)
Table B-2, page 141, the IDLE delimiter can be translated into a
RXDATA
[31:24] [23:16]
BC 95
1 0
pp pp
0 0
FDB53737 45674893
FDB53737 45674893
BC95B5B5 FDB53737
RXDATA RXDATA
[15:8] [7:0]
B5 B5
0 0
BC 95
1 0
Figure 2-29.
nnnnnnnn nnnnnnnn
nnnnnnnn nnnnnnnn
45674893 nnnnnnnn
ug024_33_091602
R
93