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

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

3.2.1.6. Inter‑Packet Gap Generation and Insertion

The TX MAC maintains the minimum inter‑packet gap (IPG) between transmitted frames required by the IEEE 802.3 Ethernet standard. The standard requires an average minimum IPG of 96 bit times (or 12 byte times). The deficit idle counter maintains the average IPG of 12 bytes.

The MAC adjusts the IPG to compensate for Alignment Marker insertion by the PHY. You can program this adjustment using the IPG_DEL_PERIOD and IPG_DEL_ENABLE registers at offsets 0x126 and 0x127, respectively. By default, the adjustment removes one Idle byte for every 16384 bytes. This removal rate corresponds to the bandwidth used by the Alignment Marker that the PHY inserts in the outgoing Ethernet communication. You can modify the value in the IPG_DEL_PERIOD register to specify more or less frequent removal of Idle bytes from the sequence.