Channel aligner – Altera Stratix GX Transceiver User Manual
Page 121
Altera Corporation
5–9
January 2005
Stratix GX Transceiver User Guide
XAUI Mode
Channel Aligner
You use the channel aligner when implementing the XAUI protocol, to
ensure that the channels are aligned. The channel aligner uses a 16-word-
deep FIFO module.
Ordered sets can be misaligned with respect to one another because of
board skew or differences between the independent clock recoveries per
serial lane. Channel alignment re-aligns the ordered sets. This process is
commonly referred to as deskew or channel bonding. Channel alignment
is accomplished by using the alignment code-group, referred to as /A/.
The /A/ code-group is transmitted simultaneously on all four lanes,
constituting an ||A|| ordered set, during idles or inter packet gaps
(IPG). XAUI receivers use these code-groups to resolve any lane to lane
skew. Skew between the lanes can be up to 40 UI (12.8ns) as specified in
the standard, which relaxes the board design constraints.
shows lane skew at the receiver input, and how the deskew circuitry uses
the /A/ code-group to deskew the channels.
Figure 5–7. Example of Lane Skew at Receiver Input
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