Other Important Design Notes; Receive Data Path 32-Bit Alignment - Xilinx RocketIO User Manual

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Other Important Design Notes

Other Important Design Notes

Receive Data Path 32-bit Alignment

The RocketIO transceiver uses the attribute ALIGN_COMMA_MSB to align protocol
delimiters with the use of comma characters (special K-characters K28.5, K28.1, and K28.7
for most protocols). Setting ALIGN_COMMA_MSB to TRUE/FALSE determines where
the comma characters appear on the RXDATA bus. When ALIGN_COMMA_MSB is set to
FALSE, the comma can appear in any byte lane of RXDATA in the 2- and 4-byte primitives.
When 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
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
into a 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
RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
TXDATA TX PCS
RXDATA RX PCS
Figure 2-28: Serial and Parallel Loopback Logic
"ALIGN_COMMA_MSB," page
Table B-1, page 135, and
Table 2-24. In the table, "pp" indicates a byte from a previous word of data.
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TX SERIALIZER
PARALLEL
LOOPBACK = 01
MUX
RX DESERIALIZER
67.)
Table B-2, page 143, the IDLE delimiter can be translated
R
TXP/TXN
SERIAL
LOOPBACK = 10
MUX
RXP/RXN
UG024_25_110503
93