40- and 100-Gbps Ethernet MAC and PHY MegaCore Function User Guide

ID 683114
Date 6/15/2022
Public
Document Table of Contents

3.2.1.1. Preamble, Start, and SFD Insertion

In the TX datapath the MAC appends an eight-byte preamble that begins with a Start byte (0xFB) to the client frame. This MAC module also incorporates the functions of the reconciliation sublayer.

The source of the 6‑byte preamble and 1‑byte SFD depends on whether you turn on the TX preamble pass-through feature by setting bit 1 of the Preamble Pass-Through Configuration register at offset 0x125 .

If the TX preamble pass-through feature is turned on, the client provides the eight-byte preamble (including Start byte and final 1-byte SFD) on the data bus. However, the IP core overwrites the Start byte the client provides, and only passes on the intermediate six bytes and the SFD. The client is responsible for providing an appropriate SFD byte.