Xilinx 7 Series User Manual

7 Series FPGAs GTP Transceivers User Guide www.xilinx.com 205
UG482 (v1.9) December 19, 2016
RX Channel Bonding
Setting the Maximum Skew
When the master receives a channel bonding sequence, it does not trigger channel bonding
immediately. Several more bytes must arrive if the slaves have more latency. This wait time
effectively becomes the maximum skew that the RX elastic buffer can handle. If the skew is greater
than this wait time, the slaves might not receive the sequence by the time the master triggers channel
bonding.
Figure 4-52 shows two FIFOs, one for the master and one for the slave. If the slave is behind the
master, the master must wait several cycles before triggering channel bonding, otherwise the slow
slave does not have the channel bonding sequence in its buffer.
CHAN_BOND_MAX_SKEW is used to set the maximum skew allowed for channel bonding
sequences 1 and 2. The maximum skew range is 1 to 14. This range must always be less than
X-Ref Target - Figure 4-51
Figure 4-51: Channel Bonding Sequence Mapping
CHAN_BOND_SEQ_x_4 CHAN_BOND_SEQ_x_3 CHAN_BOND_SEQ_x_2
CHAN_BOND_SEQ_x_1
CHAN_BOND_SEQ_x_ENABLE
4321
UG482_c4_33_111011
X-Ref Target - Figure 4-52
Figure 4-52: Channel Bonding Example (CHAN_BOND_MAX_SKEW = 2 and
Master RXCHANBONDLEVEL[2:0] = 1)
D1D2D3D4D5D6D7SEQ1
D1D2D3D4D5D6D7 D0
D4D5D6D7SEQ1D8D9D10
D4D5D6D7SEQ1D8D9 D3
D5D6D7SEQ1D8D9D10D11
D5D6D7SEQ1D8D9D10 D4
Slave
Elastic
Buffer
Master
Elastic
Buffer
Slave’s New Elastic
Buffer Read Pointer
Master receives CB Sequence
The master waits CHAN_BOND_MAX_SKEW
cycles before triggering channel bonding, giving
the slave time to receive the sequence. The
message to perform channel bonding is sent
using the RXCHBONDO port.
The RXCHANBONDLEVEL setting of the master
determines how many cycles later the bonding
operation is executed. At this time, the slave’s
elastic buffer pointers are moved so that the
output is deskewed.
Slave
Elastic
Buffer
Master
Elastic
Buffer
Slave
Elastic
Buffer
Master
Elastic
Buffer
UG482_c4_34_111011
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Xilinx 7 Series Specifications

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Brand	Xilinx
Model	7 Series
Category	Computer Hardware
Language	English