Low Latency 40G Ethernet IP User Guide: Agilex™ 5 FPGAs and SoCs

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ID 813652
Date 10/24/2025
Public
Document Table of Contents
Document Table of Contents x
1. About the Low Latency 40G Ethernet IP 2. Low Latency 40G Ethernet IP Parameters 3. Getting Started 4. Functional Description 5. Clocking and Reset Requirements 6. Interfaces and Signal Descriptions 7. Control, Status, and Statistics Register Descriptions 8. Comparison Between Various Low Latency 40G Ethernet IPs 9. Document Revision History for the Low Latency 40G Ethernet IP User Guide: Agilex™ 5 FPGAs and SoCs
1. About the Low Latency 40G Ethernet IP x
1.1. Low Latency 40G Ethernet IP Supported Features 1.2. Low Latency 40G Ethernet IP Device Family and Speed Grade Support 1.3. Resource Utilization 1.4. Release Information
1.2. Low Latency 40G Ethernet IP Device Family and Speed Grade Support x
1.2.1. Low Latency 40G Ethernet Device Family Support 1.2.2. Low Latency 40G Ethernet IP Device Speed Grade Support
3. Getting Started x
3.1. Introduction to Altera IP 3.2. Installing and Licensing IPs 3.3. Specifying the IP Parameters and Options 3.4. Simulating the IP 3.5. Generated File Structure 3.6. Integrating Your IP in Your Design 3.7. Testbench 3.8. Compiling the Full Design and Programming the FPGA
3.6. Integrating Your IP in Your Design x
3.6.1. Pin Assignments 3.6.2. Placement Settings
3.7. Testbench x
3.7.1. Understanding the Testbench Behavior
4. Functional Description x
4.1. Low Latency 40G Ethernet IP Functional Description 4.2. GTS Transceiver Configuration 4.3. Transmitter Datapath 4.4. Receiver Datapath 4.5. Flow Control 4.6. Link Fault Signaling Interface
4.3. Transmitter Datapath x
4.3.1. Transmitter MAC 4.3.2. Transmitter PCS 4.3.3. PMA
4.3.1. Transmitter MAC x
4.3.1.1. Preamble Insertion 4.3.1.2. Frame Padding 4.3.1.3. Inter-Packet Gap Generation and Insertion 4.3.1.4. Frame Check Sequence (CRC-32) Insertion 4.3.1.5. Transmitter Avalon® Streaming Filter
4.4. Receiver Datapath x
4.4.1. Receiver MAC 4.4.2. Receiver PCS
4.4.1. Receiver MAC x
4.4.1.1. IP Core Preamble Processing 4.4.1.2. IP Core CRC Checking and Dynamic Forwarding 4.4.1.3. IP Core Strict SFD Checking 4.4.1.4. Length/Type Field Processing
4.4.1.4. Length/Type Field Processing x
4.4.1.4.1. Frame Type Checking 4.4.1.4.2. Length Checking
4.5. Flow Control x
4.5.1. Transmitter Pause/PFC Flow Control Transmission 4.5.2. XON/XOFF Pause Frames
5. Clocking and Reset Requirements x
5.1. Clocks 5.2. Reset Requirements
6. Interfaces and Signal Descriptions x
6.1. Transmitter MAC Interface to User Logic 6.2. Receiver MAC Interface to User Logic 6.3. Transmitter PCS Interface to User Logic 6.4. Receiver PCS Interface to User Logic 6.5. GTS Transceivers Signals 6.6. GTS Transceiver Reconfiguration Signals 6.7. Avalon® Memory-Mapped Management Interface 6.8. Miscellaneous Status and Debug Signals 6.9. Reset Signals 6.10. Clocks 6.11. Flow Control Interface 6.12. GTS Reset Sequencer IP
7. Control, Status, and Statistics Register Descriptions x
7.1. PHY Registers 7.2. Transmitter MAC Registers 7.3. Receiver MAC Registers 7.4. Pause/PFC Flow Control 7.5. Statistics Counters 7.6. Shadow Register
1. About the Low Latency 40G Ethernet IP
2. Low Latency 40G Ethernet IP Parameters
3. Getting Started
4. Functional Description
5. Clocking and Reset Requirements
6. Interfaces and Signal Descriptions
7. Control, Status, and Statistics Register Descriptions
8. Comparison Between Various Low Latency 40G Ethernet IPs
9. Document Revision History for the Low Latency 40G Ethernet IP User Guide: Agilex™ 5 FPGAs and SoCs

4.4.1.4.2. Length Checking

The MAC Transmitter/Receiver function checks the frame and payload lengths of basic, VLAN tagged, and stacked VLAN tagged frames.

The frame length must be at least 64 (0x40) bytes and not exceed the MAX_TX_SIZE_CONFIG on MAC Transmitter or MAX_RX_SIZE_CONFIG on MAC Receiver. MAC Transmitter/Receiver does not drop frames or packet data even if an error has been detected. The MAC Transmitter/Receiver keeps track of the actual payload length as it monitoring a Transmitter/Receiver frame, and it checks the actual payload length against the length/type or client length/type field.

As the existence of padding when frame length is less than 64 bytes and over-padding when frame length is more than 64 bytes, the MAC Transmitter/Receiver does not try to match the actual payload length value with the frame length/type field value. The MAC Transmitter/Receiver marks "payload length error" only when the actual payload length is smaller than the frame length/type or client length/type field.

The MAC Transmitter/Receiver checks for the following types of length error:

  • Undersized frame error: If actual packet frame byte count is less than 64 bytes, the packet are marked as "undersized frame".
  • Oversized frame error: If actual packet frame byte count is more than MAX_TX/RX_SIZE_CONFIG, the packet is marked as "oversized frame". This applies to all packets including basic/VLAN/Stacked VLAN or other types of packets.
  • Payload length error:
    • Basic Ethernet packet:
      • If the length/type field is less than or equal to 1500 bytes, and the actual payload length is smaller than length/type field, the packet is marked as "payload length error".
      • If the length/type field is more than 1500 bytes, payload length are not checked. "Payload length error" are not marked to this kind of packets.
    • VLAN tagged frames: If the "Vlan detection" feature is disabled, "payload length error" does not apply to Vlan/Stacked Vlan packets. Otherwise, following rules applies to decide if packet has "payload length error".
      • If the length/type field is less than or equal to 1500 bytes, and the actual payload length is smaller than length/type field, the packet are marked as "payload length error".
      • If the length/type field is more than 1500 bytes, payload length are not checked. "Payload length error" are not marked to this kind of packets.
    • Control packet (0x8808): The "payload length error" does not apply to this type of packet.
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