Low Latency 40-Gbps Ethernet IP Core User Guide

ID 683745
Date 3/08/2021
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3.2.16. Low Latency 40GBASE-KR4 IP Core Variations

The LL 40GBASE-KR4 IP core supports low-level control of analog transceiver properties for link training and auto-negotiation in the absence of a predetermined environment for the IP core. For example, an Ethernet IP core in a backplane may have to communicate with different link partners at different times. When it powers up, the environment parameters may be different than when it ran previously. The environment can also change dynamically, necessitating reset and renegotiation of the Ethernet link.

The LL 40GbE IP core 40GBASE-KR4 variations implement the IEEE Backplane Ethernet Standard 802.3ap-2007 . The LL 40GbE IP core provides this reconfiguration functionality in Arria 10 devices by configuring each physical Ethernet lane with an Intel Backplane Ethernet 10GBASE-KR PHY IP core if you turn on Enable KR4 in the LL 40GbE parameter editor. The parameter is available in variations parameterized with these values:

  • Device family: Arria 10
  • Protocol speed: 40GbE
  • Enable 1588 PTP : Off

The IP core includes the option to implement the following features:

  • KR auto-negotiation provides a process to explore coordination with a link partner on a variety of different common features. The 40GBASE-KR4 variations of the LL 40GbE IP core can auto-negotiate only to a 40GBASE-KR4 configuration. Turn on the Enable KR4 Reconfiguration and Enable Auto-Negotiation parameters to configure support for auto-negotiation.
  • Link training provides a process for the IP core to train the link to the data frequency of incoming data, while compensating for variations in process, voltage, and temperature. Turn on the Enable KR4 Reconfiguration and Enable Link Training parameters to configure support for link training.

  • After the link is up and running, forward error correction (FEC) provides an error detection and correction mechanism to enable noisy channels to achieve the Ethernet-mandated bit error rate (BER) of 10-12. Turn on the Include FEC sublayer parameter to configure support for FEC.

The LL 40GBASE-KR4 IP core variations include separate link training and FEC modules for each of the four Ethernet lanes, and a single auto-negotiation module. You specify the master lane for performing auto-negotiation in the parameter editor, and the IP core also provides register support to modify the selection dynamically.

Intel provides a testbench for LL 40GBASE-KR4 IP core variations with an Avalon-ST client interface that generate their own TX MAC clock (Use external TX MAC PLL is turned off). Intel provides a hardware design example for all LL 40GBASE-KR4 IP core variations that generate their own TX MAC clock, to assist you in integrating your LL 40GBASE-KR4 IP core into your complete design. You can examine the design example for an example of how to drive and connect the 40GBASE-KR4 IP core.

IP core FEC functionality relies on register settings in the LL 40GBASE-KR4 registers and on some specific register fields in the Arria 10 device registers.

To simulate correctly and to run correctly in hardware, you must drive the reconfig_clk and the clk_status inputs from the same source clock.