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

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

3.2.11. 40-100GbE IP Core Modes of Operation

This section explains the cut-through, store and forward, and promiscuous modes of the 40-100GbE IP core.

In the normal mode of operation, the 40-100GbE IP core MAC transmits and receives data through a PHY to and from a remote link partner Ethernet MAC. You can program IP core registers to control the way in which the IP core RX MAC operates.

You can program the RX MAC to selectively filter incoming Ethernet packets based on various criteria. For example, the RX MAC performs address filtering, various header checking, and control frame termination according to the IEEE 802.3 standard. You must enable filtering to discard mismatched destination addresses.

If you choose to accept all incoming Ethernet packets, and not filter on any criterion, except possibly to filter out runt packets, the IP core is configured in cut‑through mode. If you filter based on any criterion other than runt packets, the IP core is configured in store and forward mode, in which it buffers the incoming packet for checking before processing in the MAC.

If the IP core is in cut‑through mode, it meets the criteria for promiscuous receive mode, as defined in the Ethernet standard. This definition specifies that the Ethernet implementation accept all valid frames, regardless of destination address. In cut-through mode, the IP core accepts all Ethernet frames that are sufficiently well-formed to be identified. Runt frames are invalid frames, according to the Ethernet standard, and therefore their acceptance or rejection is immaterial to the criteria for promiscuous receive mode.