2–102
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Receiver Modules
Figure 2–77. Single-Width Mode Insertion of a Skip Character
The Stratix II GX rate matcher in single-width mode has FIFO buffer
overflow and underflow protection. In the event of a FIFO buffer
overflow the rate matcher deletes any data after the overflow condition to
prevent FIFO buffer pointer corruption until the rate matcher is not full.
In an underflow condition, the rate matcher inserts 9'h1FE (/K30.7) until
the FIFO buffer is not empty. These measures ensure that the FIFO buffer
gracefully exits the overflow and underflow condition without requiring
a FIFO buffer reset.
Double-Width General Rate Matching
In double-width mode, the rate matcher can support up to ±300 PPM
differences between the upstream transmitter and the receiver. The rate
matcher looks for the skip ordered set, which is usually a /K28.5/ comma
followed by programmable neutral disparity skip characters (for
example, /K28.0/). For general rate matching, you can customize the SOS
to support a variety of protocols, including custom protocols. The SOS
must contain a valid control code group (Kx.y), followed by any neutral
disparity skip code group (any Kx.y or Dx.y of neutral disparity, for
example, K28.0). The rate matcher deletes or inserts dual skip characters
when necessary to prevent the rate matching FIFO buffer from
overflowing or underflowing.
The rate matcher deletes skip characters by pairs when they appear on the
upper and lower bytes at the same time. There are no other restrictions for
the deletion of skip characters.
Figure 2–78
shows an example of deleting
two skip characters.
K28.5
K28.0
K28.0
K28.0
K28.0
K28.0
Dx.y
K28.5
datain
clock
K28.5
K28.0
K28.0
K28.0
K28.0
K28.0
Dx.y
K28.5
dataout
One Skip Inserted
K28.0
Dx.y
K28.0
K28.0
One Skip Inserted