10–4
Chapter 10: Optional Features
Lane Initialization and Reversal
Stratix V Hard IP for PCI Express
June 2012
Altera Corporation
Lane Initialization and Reversal
Connected components that include IP blocks for PCI Express need not support the
same number of lanes. The ×4 variations support initialization and operation with
components that have 1, 2, or 4 lanes. The ×8 variant supports initialization and
operation with components that have 1, 2, 4, or 8 lanes.
The Stratix V Hard IP for PCI Express supports lane reversal, which permits the
logical reversal of lane numbers for the ×1, ×2, ×4, and ×8 configurations. Lane
reversal allows more flexibility in board layout, reducing the number of signals that
must cross over each other when routing the PCB.
summarizes the lane assignments for normal configuration.
summarizes the lane assignments with lane reversal.
illustrates a PCI Express card with ×4 IP Root Port and a ×4 Endpoint on
the top side of the PCB. Connecting the lanes without lane reversal creates routing
problems. Using lane reversal, solves the problem.
Table 10–3. Lane Assignments without Lane Reversal
Lane Number
7
6
5
4
3
2
1
0
×8 IP core
7
6
5
4
3
2
1
0
×4 IP core
—
—
—
—
3
2
1
0
×1 IP core
—
—
—
—
—
—
—
0
Table 10–4. Lane Assignments with Lane Reversal
Core Config
8
4
1
Slot Size
8
4
2
1
8
4
2
1
8
4
2
1
Lane
assignments
7:0,6:1,5:2,4:3,3:4,
2:5,1:6,0:7
3:4,2:5,
1:6,0:7
1:6,
0:7
0:7
7:0,6:1,
5:2,4:3
3:0,2:1,
1:2,0:3
3:0,
2:1
3:0
7:0
3:0
1:0
0:0
Figure 10–2. Using Lane Reversal to Solve PCB Routing Problems
0
1
2
3
Root Port
3
2
1
0
Endpoint
0
1
2
3
Root Port
0
1
2
3
Endpoint
No Lane Reversal
Results in PCB Routing Challenge
With Lane Reversal
Signals Route Easily
lane
reversal
no lane
reversal