2–100
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Receiver Modules
In the event the rate matching FIFO buffer in the GIGE mode approaches
overflow or underflow, the transceiver outputs a sequence code group
(9'h19C)—8'h9C on
rx_dataout
and 1'b1 on
rx_ctrldetect
. The
rx_digitalreset
signal must be asserted to reset the rate matcher
FIFO buffer.
PIPE Mode
In PIPE mode, the rate matcher supports up to ±300 PPM (600 PPM total)
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 three /K28.0/ skip characters. The rate matcher deletes or
inserts skip characters when necessary to prevent the rate-matching FIFO
buffer from overflowing or underflowing.
The rate matcher can delete only one skip character in a consecutive
cluster of skip characters in PIPE mode only.
Figure 2–69
shows a PIPE
mode rate matcher deletion of two skip characters.
Figure 2–75. PIPE Mode With Two Deletions (One Per Cluster)
The rate matcher can perform skip character insertion one insertion per
skip cluster in PIPE mode. There is no limit on the consecutive number of
skip characters allowed per skip cluster.
The Stratix II GX rate matcher in PIPE 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
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.
K28.5
K28.0
K28.0
K28.0
Dx.y
K28.5
K28.0
K28.0
datain
Skip Cluster
Skip Cluster
Skip Cluster
Skip Cluster
K28.5
K28.0
K28.0
Dx.y
K28.5
K28.0
Dx.y
Dx.y
dataout
Two Skips Deleted