Achronix Speedster22i SerDes - Manual (Page 25)

Deskew FIFO
The deskew block provides support for standards which require multiple lane bonding and
de-skewing of received data across multiple lanes. Lane bonding is required when the users
want to transmit data faster than is possible by using one serial link (lane). In such case, the
data is received must be aligned across the lanes. Deskew module within the SerDes takes
care of this.
Figure 14: Operating principle of deskew technique
“Figure 14 - Operating principle of deskew technique” shows the operating principle of
deskew operation. In this figure, data is being sent using four lanes. On the receiver side,
before lane-bonding, we find that the data at time t+2on lane-1 is aligned with data at time
t+1 on lane-2 and so on. The deskew technique aims to align the data with respect to the clock
cycles. In other words, data at time t+2on lane-2 should be aligned with data at time t+2 on
the other lanes. The red lines for the clock at receiver end demonstrates this.
For lane bonding, all lanes should use the same reference clock and insert de-skew characters
at the same time on each lane. Skew between lanes is introduced by both active (CDR) and
passive (board) elements of the link. The deskew operation can result in some loss of data
when it aligns characters to the same clock cycle.
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