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. IP Core TX Datapath

The TX MAC module receives the client payload data with the destination and source addresses and then adds, appends, or updates various header fields in accordance with the configuration specified. The MAC does not modify the destination address or the payload received from the client. However, the TX MAC module adds a preamble (if the IP core is not programmed to receive the preamble from user logic), pads the payload of frames greater than eight bytes to satisfy the minimum Ethernet frame payload of 46 bytes, and calculates the CRC over the entire MAC frame. (If padding is added, it is also included in the CRC calculation). The TX MAC module can also modify the source address, and always inserts IDLE bytes to maintain an average IPG.

Figure 10. Typical Client Frame at the Transmit InterfaceIllustrates the changes that the TX MAC makes to the client frame. This figure uses the following notational conventions:
  • <p> = payload size = 0–1500 bytes, or 9600 bytes for jumbo frames.
  • <s> = padding bytes = 0–46 bytes.
  • <g> = number of IPG bytes

The following sections describe the functions that the TX module performs: