Xilinx RocketIO User Manual

RocketIO™ Transceiver User Guide www.xilinx.com 93
UG024 (v3.0) February 22, 2007
Other Important Design Notes
R
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 “ALIGN_COMMA_MSB,” page 67.)
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 Table B-1, page 135, and Table B-2, page 143, the IDLE delimiter can be translated
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 Table 2-24. In the table, “pp” indicates a byte from a previous word of data.
Figure 2-28: Serial and Parallel Loopback Logic
TXDATA
RXDATA
TXP/TXN
RXP/RXN
TX PCS TX SERIALIZER
RX DESERIALIZER
RX PCS MUX
MUX
PARALLEL
LOOPBACK = 01
SERIAL
LOOPBACK = 10
UG024_25_110503
Product Not Recommended for New Designs

Xilinx RocketIO Specifications

General

Brand	Xilinx
Model	RocketIO
Category	Transceiver
Language	English