188.8.131.52. TX Preamble, Start, and SFD Insertion
In the TX datapath the MAC appends an eight-byte preamble that begins with a Start byte (0xFB) to the client frame. If you turn on Link fault generation option, this MAC module also incorporates the functions of the reconciliation sublayer.
The source of the preamble depends on whether you enable the preamble pass-through feature by turning on Enable preamble passthrough in the F-Tile Ethernet Intel® FPGA Hard IP parameter editor.
If the preamble pass-through feature is turned on, the client must provide 8 preamble bytes (including an SFD byte) on the data bus. The MAC will automatically replace the Start Control byte.