Rx_Buffer_Use; Clk_Cor_Seq_ - Xilinx RocketIO User Manual

Product Not Recommended for New Designs
R
Clock correction may be used with other encoding protocols, but they must have a 10-bit
alignment scheme. This is required so the comma detection logic can properly align the
data in the elastic buffer, allowing the clock correction logic to properly read out data to the
FPGA fabric.

RX_BUFFER_USE

The RX_BUFFER_USE attribute controls if the elastic buffer is bypassed or not. Most
applications use this buffer for clock correction and channel bonding. (See
Bonding (Channel Alignment)," page
set to TRUE, since this buffer allows a way to cross the clock domains of RXRECCLK and
the fabric RXUSRCLK/RXUSRCLK2.

CLK_COR_SEQ_ * _ *

To accommodate many different protocols, the MGT features programmability that allows
it to detect a 1-, 2-, or 4-byte clock correction sequence (CCS), such as may be used in
Gigabit Ethernet (2-byte) or Fibre Channel (4-byte). The attributes CLK_COR_SEQ_*_*
and CLK_COR_SEQ_LEN (below) define the CCS that the PCS recognizes. Both SEQ_1
and SEQ_2 can be used at the same time if multiple CCSs are required. As shown in
Table
used, the other for when 8B/10B encoding is bypassed. The most significant bit of the CCS
determines whether it is applicable to an 8-bit (encoded) or a 10-bit (unencoded) sequence.
These sequences require that the encoding scheme allows the comma detection and
alignment circuitry to properly align data in the elastic buffer. (See
"CLK_CORRECT_USE", above). The bit definitions are the same as shown earlier in the
Vitesse channel-bonding example. (See
Table 2-15: Clock Correction Sequence / Data Correlation for 16-Bit Data Port
CLK_COR_SEQ_1_1
CLK_COR_SEQ_1_2
CLK_COR_SEQ_1_3
CLK_COR_SEQ_1_4
74
2-15, the example CCS has two possible modes, one for when 8B/10B encoding is
Attribute Settings
CLK_COR_SEQ 8-Bit Data Mode
00110111100
00010010101
00010110101
00010110101
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Chapter 2: Digital Design Considerations
79.) It is recommended that this attribute always be
"Receiving Vitesse Channel Bonding
Character
10-Bit Data Mode
(8B/10B Bypass)
K28.5
10011111010
D21.4
11010100010
D21.5
11010101010
D21.5
11010101010
RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
"Channel
Sequence.")
TXDATA
CHARISK
(hex)
1 BC
95
0
Β5
0
Β5
0