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

ID 813652
Date 4/01/2024
Public
Document Table of Contents

4.6.1. Frame Type Checking

The MAC TX/RX checks the length/type field to determine the frame type:
  • Length/type ≤ 0x5DC(1500): The field represents the payload length of a basic Ethernet frame. The MAC TX/RX continues to check the frame and payload lengths.
  • 0x5DC(1500) < Length/type < 0x600(1536): The frames with payloads size in this range are not a standard basic Ethernet frame, nor they are legal control packets. The payload length is not checked for this kind of packets.
  • Length/type ≥ 0x600 (1536): The field represents the frame type instead of frame payload length
    • Length/type = 0x8100. VLAN or stacked VLAN tagged frames. The MAC TX/RX continues to check the frame and payload lengths.
    • Length/type = 0x8808. Control frames. The next two bytes are the Opcode field which indicates the type of control frame. For pause frames (Opcode = 0x0001) and PFC frames (Opcode = 0x0101), the MAC RX proceeds with pause frame processing.
    • For other field values, the MAC RX forwards the receive frame to the client. If the length/type is less than payload, the MAC RX considers the frame to have excessive padding and does not assert rx_error[4].