Low Latency 40-Gbps Ethernet IP Core User Guide

ID 683745
Date 3/08/2021
Document Table of Contents Frame Check Sequence (CRC-32) Insertion

The TX MAC computes and inserts a CRC32 checksum in the transmitted MAC frame. The frame check sequence (FCS) field contains a 32-bit CRC value. The MAC computes the CRC32 over the frame bytes that include the source address, destination address, length, data, and pad (if applicable). The CRC checksum computation excludes the preamble, SFD, and FCS. The encoding is defined by the following generating polynomial:

FCS(X) = X32 +X26 +X23 +X22 +X16 +X12 +X11 +X10 +X8 +X7 +X5 +X4 +X2 +X1 +1

CRC bits are transmitted with MSB (X32) first.

If you configure your LL 40GbE IP core with no flow control, you can configure your IP core TX MAC to implement TX CRC insertion or not, by turning Enable TX CRC insertion on or off in the LL 40GbE parameter editor. By default, the CRC insertion feature is enabled. In variations with flow control, CRC insertion is enabled.