Low Latency 40-Gbps Ethernet IP Core User Guide

ID 683745
Date 3/08/2021
Document Table of Contents LL 40GbE IP Core Preamble Processing

The preamble sequence is Start, six preamble bytes, and SFD. If this sequence is incorrect the frame is ignored. The Start byte must be on receive lane 0 (most significant byte). The IP core uses the SFD byte (0xD5) to identify the last byte of the preamble. The MAC RX looks for the Start, six preamble bytes and SFD.

By default, the MAC RX removes all Start, SFD, preamble, and IPG bytes from accepted frames. However, if you turn on Enable preamble passthrough in the LL 40GbE parameter editor, the MAC RX does not remove the eight-byte preamble sequence.

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