Altera Corporation
2–97
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
Channel Aligner (Deskew)
The channel aligner is automatically used when implementing the XAUI
protocol to ensure that the channels are aligned with respect to each other.
The channel aligner uses a 16-word-deep FIFO buffer.
1
The channel aligner is only available in the XAUI mode.
It is possible for ordered sets to be misaligned with respect to one another
because of board skew or differences between the independent clock
recoveries per serial lane. Channel alignment, also referred to as deskew
or channel bonding, realigns the ordered sets 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.
Figure 2–72
shows lane skew at the receiver input and
how the deskew circuitry uses the /A/ code group to deskew the
channels.
Figure 2–72. Lane Deskew With /A/ Code Group
Stratix II GX devices manage XAUI channel alignment with a dedicated
deskew macro that consists of a 16-word-deep FIFO buffer that is
controlled by a XAUI deskew state machine. The XAUI deskew state
machine first looks for the /A/ code group within each channel. When
the XAUI deskew state machine detects /A/ in each channel, the deskew
FIFO buffer is enabled. The deskew state machine now monitors the
reception of /A/ code groups. When four aligned /A/ code groups are
received, the
rx_channelaligned
signal is asserted. The deskew state
machine continues to monitor the reception of /A/ code groups and
de-asserts the
rx_channelaligned
signal if alignment conditions are
Lanes are
Deskewed by
Lining up
the "Align"/A/,
Code Groups
Lanes Skew at
Receiver Input
A
Lane 0
K
K
R
A
K
R
R
K
K
K
R
R
Lane 1
K
K
R
A
K
R
R
K
K
K
R
R
Lane 0
K
K
R
K
R
R
K
K
K
R
R
Lane 1
K
K
R
A
K
R
R
K
K
K
R
R
Lane 2
K
K
R
A
K
R
R
K
K
K
R
R
Lane 3
K
K
R
A
K
R
R
K
K
K
R
R
Lane 2
K
K
R
A
K
R
R
K
K
K
R
R
Lane 3
K
K
R
A
K
R
R
K
K
K
R
R
Содержание Stratix II GX
Страница 640: ...4 244 Altera Corporation Stratix II GX Device Handbook Volume 2 October 2007 Document Revision History ...
Страница 642: ...4 246 Altera Corporation Stratix II GX Device Handbook Volume 2 October 2007 Document Revision History ...
Страница 672: ...6 14 Altera Corporation Stratix II GX Device Handbook Volume 2 October 2007 Document Revision History ...