22.214.171.124. TX Gearbox, TX Bitslip and Polarity Inversion
The TX gearbox adapts the PCS data width to the smaller bus width of the PCS-PMA interface (Gearbox Reduction). It supports different ratios (FPGA fabric-PCS Interface Width: PCS-PMA Interface Width) such as 66:32, 66:40, 64:32, 40:40, 32:32, 64:64, 67:64, and 66:64. The gearbox mux selects a group of consecutive bits from the input data bus depending on the gearbox ratio and the data valid control signals.
The TX gearbox also has a bit slipping feature to adjust the data skew between channels. The TX parallel data is slipped on the rising edge of tx_enh_bitslip before it is passed to the PMA. The maximum number of the supported bitslips is PCS data width-1 and the slip direction is from MSB to LSB and from current to previous word.
You can use transmitter data polarity inversion to invert the polarity of every bit of the input data word to the serializer in the transmitter path. The inversion has the same effect as swapping the positive and negative signals of the differential TX buffer. This is useful if these signals are reversed on the board or backplane layout. Enable polarity inversion through the Native PHY IP core.