Altera Corporation
2–99
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
The transceiver block can operate in multi-crystal environments, which
can tolerate frequency variations of ± 300 PPM between crystals.
Stratix II GX devices have embedded circuitry to perform clock rate
compensation. Clock rate compensation is achieved by inserting or
removing skip characters from the IPG or idle streams. This process is
called rate matching or clock rate compensation.
The rate matcher in the transceiver consists of a 20-word-deep FIFO
buffer and necessary logic to detect and perform the insertion and
deletion functions.
XAUI
The rate matcher in XAUI mode operates in a synchronized ×4 mode and
supports up to a ±100 PPM clock difference between the upstream
transmitter and receiver. In this mode, the rate matcher can insert or
delete a column of /R/ characters as denoted by the ||R|| designation,
depending on whether the FIFO buffer is approaching an empty or full
condition. The rate matcher does not operate until the XAUI
synchronization state machine achieves word alignment and channel
alignment. Until that point, the rate matcher is not active (read and write
pointers do not move).
If the ||R|| code words are not received on all channels, rate matching
does not occur and may lead to over/underflow conditions in the rate
matching FIFO buffer. If this situation occurs, the data output of the
receiver outputs a constant 9'h19C (8'h9C on the
rx_dataout
output
and 1'b1 on the
rx_ctrldetect
output) in lane 0 (rest of the lane are
data 8'h00). The receiver digital reset must be asserted and the lanes
resynchronized before data can be received.
GIGE
The rate matcher in GIGE mode operates in a channel-by-channel mode
and supports up to a ± 100 PPM clock difference between the upstream
transmitter and the receiver. The rate matcher either inserts or deletes the
/I2/ ordered set depending on whether the FIFO buffer is approaching
an empty or full condition. The /I2/ order set consists of a /K28.5+/ code
group and a /D16.2-/ code group (the sign after the code group signifies
the running disparity at the end of the code group). The rate matcher in
GIGE mode waits until the GIGE synchronization state machine achieves
synchronization. Once synchronization is achieved, the rate matcher is
active.
Содержание Stratix II GX
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