2–166
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Native Modes
1
Unlike regular PIPE mode, the Quartus II software in
low-latency PIPE mode does not automatically clock the
transmitter and receiver phase compensation FIFO write and
read clock with the
tx_clkout
signal from channel 0. You must
use the
Shared Clock Grouping
or
0 PPM Clock Grouping
assignments to manually clock the phase compensation FIFOs.
Refer to
“PLD-Transceiver Interface Clocking” on page 2–119
for
more information on clock grouping.
PIPE Reverse Parallel Loopback
In normal PIPE mode, if the transceiver is in P1 power state, a high value
on the
tx_rxdetectloop
signal forces a reverse parallel loopback as
discussed in
“PCI Express PIPE Reverse Parallel Loopback” on
page 2–206
. Parallel data at the output of the receiver rate match FIFO
gets looped back to the input of the transmitter serializer.
In low-latency PIPE mode, since the rate match FIFO is bypassed, this
feature is not supported. A high value on the
tx_rxdetectloop
signal,
when the transceiver is in P1 power state, will not force it to perform
reverse parallel loopback.
Link Width Negotiation
In normal multi-lane (×4 and ×8) PIPE configuration, the receiver phase
compensation FIFO control signals (for example,
write/read enable
)
are shared among all lanes within the link. As a result, all lanes are truly
bonded and the lane-lane skew meets the PCI Express specification.
In low-latency PIPE configuration, the receiver phase compensation FIFO
of individual lanes do not share control signals. The write port of the
receiver phase compensation FIFO of each lane is clocked by its recovered
clock. As a result, the lanes within a link are not bonded. You should
perform external lane de-skewing to ensure proper link width
negotiation.
PIPESTATUS Signal
Since the rate match FIFO is bypassed in low-latency PIPE mode, status
signal combinations related to the rate match FIFO on
pipestatus[2:0]
port become irrelevant and must not be interpreted
(
Table 2–37
).
Table 2–37. Normal and Low-Latency PIPE Status (Part 1 of 2)
pipestatus[2:0]
Normal PIPE
Low-Latency PIPE
000
Received Data OK
Received Data OK
001
Not supported
Not supported