SerialLite II IP Core User Guide

ID 683179
Date 7/13/2021
Public
Document Table of Contents

2.8.8. Lane Polarity and Order Reversal

The SerialLite II protocol optionally allows the link to recover from some connection problems.

Lane polarity and lane order are reversed automatically.

Lane Polarity

Each lane consists of a differential pair of signals. It is possible for the positive and negative sides of this pair to be reversed because of a layout error or because it simplifies layout. The SerialLite II logic can compensate for such a reversed lane on the receive side. This reversal occurs during link initialization and remains in place for as long as the link is active.
  • For training sequence one, the TID field normally read as /T1/ (D10.2) is read as /!T1/ (D21.5) when the lane polarity is inverted.
  • For training sequence two, the TID field normally read as /T2/ (D5.2) is read as /!T2/ (D26.5) when the lane polarity is inverted.

In these training sequences, the /COM/ character is followed by seven valid data characters. The last character of the sequence is used to determine the parity. If any of the parity identifiers in any lane is either /!T1/ (D21.5) or /!T2/ (D26.5), the receiver for that lane inverts the polarity.

Lane Order

The order of lanes may be incorrect due to layout errors. It may also be reversed, with the most significant lane of one end of the link connected to the least significant lane of the other end, due to layout constraints. The SerialLite II logic always detects a lane order mismatch, and compensates for the reversed lane order on the receive side. This reversal occurs during link initialization and remains in place for as long as the link is active.

The SerialLite II logic only corrects reversed lane order. If the lane order is scrambled, the receiving end cannot unscramble it. The following example shows a possible four-lane system, where Serial Lite II can reverse the four-lane system:
Lane 0 -> Lane 3
Lane 1 -> Lane 2
Lane 2 -> Lane 1
Lane 3 -> Lane 0