Other Important Design Notes; Receive Data Path 32-Bit Alignment; Figure 3-19: Rxdata Aligned Correctly; Table 3-19: 32-Bit Rxdata, Aligned Versus Misaligned - Xilinx RocketIO User Manual

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 the ALIGN_COMMA_MSB to TRUE/FALSE determines
where the comma characters appear on the RXDATA bus. A setting of
ALIGN_COMMA_MSB = FALSE allows the comma to appear in any byte lane of the
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.
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.
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

Table 3-19: 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
UG024 (v1.5) October 16, 2002
RocketIO™ Transceiver User Guide
Table 3-13, page 61, and
Table 3-19. 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 3-19: RXDATA Aligned Correctly

www.xilinx.com
1-800-255-7778
Table 3-14, page 69, the IDLE delimiter can be translated
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 3-19.
nnnnnnnn nnnnnnnn
nnnnnnnn nnnnnnnn
nnnnnnnn
45674893
ug024_33_091602
R
75