You may see the following Quartus® II software fitter error when using the transceiver PHY instance, and the “enable Byte Serializer/Deserializer with 16- and 20-Bit PMA-PCS Widths” option is selected on Cyclone® V GX/SX, -6 transceiver, and -8 device speed grade devices.
Error: Standard RX PCS Parameter 'hd_pcs8g_digi_rx_byte_deserializer' is set to an illegal value of 'en_bds_by_2'. This mode is not supported with device speed grade of '8_H6', PMA WIDTH of 'twenty_bit' on atom '<variation name>|av_hssi_8g_rx_pcs_rbc:inst_av_hssi_8g_rx_pcs|wys'.
Error: Standard TX PCS Parameter 'hd_pcs8g_digi_tx_byte_serializer' is set to an illegal value of 'en_bs_by_2'. This mode is not supported with device speed grade of '8_H6', PMA WIDTH of 'twenty_bit' on atom '<variation name>|av_hssi_8g_tx_pcs_rbc:inst_av_hssi_8g_tx_pcs|wys '.
This combination of -6 transceiver and -8 device speed grades is unsupported when the “enable Byte Serializer/Deserializer with 16- and 20-Bit PMA-PCS Widths” option is selected.
To work around this problem, you can reduce your transceiver PHY parallel width.