126.96.36.199. IP Core Preamble Processing
If you turn on Enable preamble passthrough in the parameter editor, the RX MAC forwards preamble bytes. The TX MAC requires the preamble bytes to be included in the frames at the Avalon® Streaming interface.
In preamble pass-through mode, l2_rx_preamble[63:0] provides the received preamble data to the client. When l2_rx_startofpacket is asserted, the l2_rx_preamble[63:0] drives the preamble data and l2_rx_data[127:0] drives the first 16 bytes of frame data, starting from destination address. The l2_rx_preamble[63:0] bus is only present in preamble pass-through mode.
If you turn off Enable preamble passthrough, the IP core removes the preamble bytes. l2_rx_startofpacket is aligned to the MSB of the destination address.
Note that a single parameter in the 50GbE parameter editor turns on both RX and TX preamble passthrough.