HC4GX15 Datasheet, PDF (424/668 Pages) Altera Corporation – HardCopy IV Device Handbook

1–160
Chapter 1: HardCopy IV GX Transceiver Architecture
Functional Modes
Rate Match FIFO
In XAUI mode, the rate match FIFO is capable of compensating for up to ±100 PPM
(200 PPM total) difference between the upstream transmitter and the local receiver
reference clock. The XAUI protocol requires the transmitter to send /R/ (/K28.0/)
code groups simultaneously on all four lanes (denoted as ||R|| column) during
inter-packet gaps, adhering to rules listed in the IEEE P802.3ae specification. The rate
match FIFO operation in XAUI mode is compliant to the IEEE P802.3ae specification.
The rate match operation begins after:
■ The synchronization state machine in the word aligner of all four channels
indicates synchronization has been acquired by driving the rx_syncstatus
signal high
■ The deskew FIFO indicates alignment has been acquired by driving the
rx_channelaligned signal high
The rate match FIFO looks for the ||R|| column (simultaneous /R/ code group on
all four channels) and deletes or inserts ||R|| column to prevent the rate match FIFO
from overflowing or under-running. The rate match FIFO can insert or delete as many
||R|| columns as necessary to perform the rate match operation.
Two flags, rx_rmfifodatadeleted and rx_rmfifodatainserted, indicating
rate match FIFO deletion and insertion events, respectively, are forwarded to the core
fabric. If an ||R|| column is deleted, the rx_rmfifodeleted flag from each of the
four channels goes high for one clock cycle per deleted ||R|| column. If an ||R||
column is inserted, the rx_rmfifoinserted flag from each of the four channels
goes high for one clock cycle per inserted ||R|| column.
Figure 1–128 shows an example of rate match deletion in the case where three ||R||
columns are required to be deleted.
Figure 1–128. Rate Match Deletion in XAUI Mode
datain[3]
K28.5
K28.3
K28.5
First ||R||
Column
K28.0
K28.5
Second ||R|| Third ||R|| Fourth ||R||
Column
Column
Column
K28.0
K28.0
K28.0
K28.5
datain[2]
datain[1]
K28.5
K28.5
K28.3
K28.3
K28.5
K28.5
K28.0
K28.0
K28.5
K28.5
K28.0
K28.0
K28.0
K28.0
K28.0
K28.0
K28.5
K28.5
datain[0]
K28.5
K28.3
K28.5
K28.0
K28.5
K28.0
K28.0
K28.0
K28.5
dataout[3]
dataout[2]
dataout[1]
dataout[0]
K28.5
K28.5
K28.5
K28.5
rx_rmfifodatadeleted
K28.3
K28.3
K28.3
K28.3
K28.5
K28.5
K28.5
K28.5
K28.5
K28.5
K28.5
K28.5
K28.0
K28.0
K28.0
K28.0
K28.5
K28.5
K28.5
K28.5
HardCopy IV Device Handbook Volume 3
© June 2009 Altera Corporation