F-Tile Ethernet Intel® FPGA Hard IP User Guide

ID 683023
Date 12/19/2022
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4.2.1.7. TX Packing Logic

Attention: To achieve the maximum throughput when using the TX MAC segmented interface, the input packets must be packed tightly, leaving no idle segments in between.

TX Packing Logic Features

The F-Tile Ethernet Intel® FPGA Hard IP TX packing for transmit direction can be implemented in MAC segmented mode. This feature is implemented in soft logic.

  • Figure 6. Enable TX Packing IP Parameter Editor
    Note: Enable TX packing feature is not available when PTP is turned on.
  • TX packing in MAC segmented mode is implemented for all rates ranging from 40G to 400G (MAC segmented interface width of 128b and above) when PTP is NOT enabled. As a result of this new logic, IP resource utilization will increase by:
    • 205 ALMs for 40GE/50GE
    • 791 ALMs for 100GE
    • 2583 ALMs for 200GE
    • 7281 ALMs for 400GE
  • The TX packing logic adds an additional ~30 cycles of i_clk_tx latency.
  • The TX Packing feature is disabled by default to ensure backward compatibility with the previous IP version. If you do not want to run the IP at full traffic throughput, use the disable option for lower IP utilization and latency. The maximum TX MAC throughput is reduced when sending unpacked data with idle segments in between packets while TX packing is disabled.
  • When unpacked data is generated on the TX MAC segmented interface, the TX packing enabled IP to meet close to 100% line rate of all traffic with no drops or corruptions.

TX MAC Segmented Client Interface with Disabled TX Packing

To achieve close to 100% line rate without using the TX packing logic, you must implement your own packing logic on the MAC segmented interface as shown below.

The figure below depicts an example of 100GE packet data on the MAC segmented interface.

  • The box on the left shows an example of loosely packed data with 2-3 idle segments in between two packets.
  • The box on the right shows that data is packed with no idle segments between two packets. Pack the IPs input as shown in the right figure.
Figure 7. TX MAC Segmented Client Interface with Disabled TX Packing