L- and H-Tile Transceiver PHY User Guide

ID 683621
Date 1/30/2024
Document Table of Contents Block Synchronizer

PMA parallelization occurs at arbitrary word boundaries. Consequently, the parallel data from the RX PMA CDR must be realigned to meaningful character boundaries. The PCI-Express 3.0 base specification outlines that the data is formed using 130-bit blocks, with the exception of SKP blocks.

The SKP Ordered Set can be 66, 98, 130, 162, or 194 bits long. The block synchronizer searches for the Electrical Idle Exit Sequence Ordered Set (or the last number of fast training sequences (NFTS) Ordered Set) or skip (SKP) Ordered Set to identify the correct boundary for the incoming stream and to achieve the block alignment. The block is realigned to the new block boundary following the receipt of a SKP Ordered Set, as it can be of variable length.