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

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

3.2.3.1. 40-100GbE IP Core RX Filtering

The 40-100GbE IP core can operate in cut-through mode or in store and forward mode. In cut‑through mode, the IP core does not buffer incoming Ethernet packets for filtering. It can filter out incoming runt packets, but cannot filter on any other criteria. The value in bit 0 of the RX_FILTER_CTRL register at offset 0x103 determines the mode, and the value in bit 3 determines whether the IP core filters runt packets.

When the IP core is in cut‑through mode, it does not filter incoming Ethernet packets based on destination address. Therefore, when in cut-through mode, the IP core is in promiscuous receive mode. The Ethernet standard definition of promiscuous receive mode requires that the IP core accept all valid frames, regardless of destination address. The 40-100GbE IP core accepts or rejects invalid frames based on the filtering criteria that are turned on.

In store and forward mode, you can enable oversized-frame handling. When the maximum frame size is set to 9600 bytes, the IP core passes some of the frames between 9601-9644 bytes in size, and drops frames of 9645 bytes or more. For the 100GbE IP core, if the frame size is within 44 bytes over the specified maximum frame size, it may or may not be dropped, but oversized frames of over 44 bytes will always be dropped. For the 40GbE IP core, if the frame size is within 20 bytes over the specified maximum frame size, it may or may not be dropped, but oversized frames of over 20 bytes will always be dropped.

The 40-100GbE IP core supports the following filtering options:

  • Destination address mismatch—refer to the descriptions of the RX_FILTER_CTRL register and the MADDR_CTRL register and the link below to the Address Checking topic.
  • Runt frame—refer to the description of the dout_runt_last_data signal.
  • Oversized frame—refer to the preceding description.
  • Pause packet
  • Control packet
  • FCS error