The integrated block supports limited lane reversal capabilities and therefore provides flexibility in the design of the board for the link partner. The link partner can choose to lay out the board with reversed lane numbers and the integrated block continues to link train successfully and operate normally. The configurations that have lane reversal support are x8 and x4 (excluding downshift modes). Downshift refers to the link width negotiation process that occurs when link partners have different lane width capabilities advertised. As a result of lane width negotiation, the link partners negotiate down to the smaller of the advertised lane widths. The following table describes the several possible combinations including downshift modes and availability of lane reversal support.
| Integrated Block Advertised Lane Width | Negotiated Lane Width | Lane Number Mapping (Endpoint c) | Lane Reversal SupportedLane 0... Lane 7 | |
|---|---|---|---|---|
| Endpoint | Link Partner | |||
| x8 | x8 | Lane 0... Lane 7 | Lane 7... Lane 0 | Yes |
| x8 | x4 | Lane 0... Lane 3 | Lane 7... Lane 4 | No 1 |
| x8 | x2 | Lane 0... Lane 3 | Lane 7... Lane 6 | No 1 |
| x4 | x4 | Lane 0... Lane 3 | Lane 3... Lane 0 | Yes |
| x4 | x2 | Lane 0... Lane 1 | Lane 3... Lane 2 | No 1 |
| x2 | x2 | Lane 0... Lane 1 | Lane 1... Lane 0 | Yes |
| x2 | x1 | Lane 0... Lane 1 | Lane 1 | No 1 |
|
||||