MACsec Intel® FPGA IP User Guide

ID 736108
Date 4/03/2023

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4.6. Switching Port Muxes between Store and Forward and Cut-Through Modes

As part of the MACsec Authentication procedure, the Port Muxes on both the Common Port and the Controlled Port must be switched from “Store and Forward” mode to “Cut-Through” mode. Following Authentication, the Port Muxes must be switched back to “Store and Forward” mode.

In addition, if you intend to send packets that are integrity-protected only on a particular port, that Port Mux must be configured to “Store and Forward” mode as well.

To do this, you must access each Port Mux’s CSR space.

The table below provides an overview of the address space for each Port Mux.
Table 28.  Port Mux Address Map
Mux Port Number Mux Management Address Offset Register Name
The register definition for the P<n>_STORE_AND_FORWARD register is shown below. Note that N can range from 0 to 63, depending on how many ports are enabled in your design.
Table 29.  Port Mux STORE_AND_FORWARD Register
Register Description Address Bit Description SW Access Reset


Store and Forward Control Register 0x300 + 4*N[63:1] Reserved Reserved 63’h0
0x300 + 4*N[0]

Store and Forward Control Register

1’b0: Port is in Cut-Through Mode

1’b1: Port is in Store and Forward Mode
Read-Write 1’b1
The management interfaces that are used to access each port mux are shown below.
Table 30.  Port Mux Management Interfaces
Interface Name Port Mux
Decrypt Port Mux Management Interface Common Port
Encrypt Port Mux Management Interface Controlled Port
The procedure below illustrates how to change Port 2 of the Decrypt Port Mux to the “Cut Through” Mode:
  • Using the “rx_mux_app_pp_lite*” management bus, write 64’h0 to address offset 0x308.
The procedure below illustrates how to change Port 1 of the Encrypt Port Mux to the “Store and Forward” Mode:
  • Using the “tx_mux_app_pp_lite*” management bus, write 64’h1 to address offset 0x304.