Cut Through Mode

During Cut Through mode, the Triple Speed Ethernet MAC core starts transmitting an Ethernet frame before the entire packet has been received on the AXI4-stream interface. This reduces latency compared to Store Forward mode.

Cut-Through Mode is available when the AXI data width matches the PHY data width and the transmit FIFO is disabled:
  • AXI4 Data Width = 8, PHY Interface = 8-bit GMII
  • AXI4 Data Width = 16, PHY Interface = 16-bit GMII (SGMII)

If an error occurs during transmission in this mode, the MAC terminates the frame as an error frame. See Terminating Bad TX Frames for details.

Figure 1. Cut Through Mode