This tests the following mode combinations:
•PRBS-7 (On 8B/10B encoding, all possible internal data widths) > PRBSSEL (001)
•PRBS-15 (On 8B/10B encoding, all possible internal data widths) > PRBSSEL (010)
•PRBS-23 (none for 8B/10B encoding) > PRBSSEL (011)
•PRBS-31 (none for 8B/10B encoding) > PRBSSEL (100)
•PCIe compliance pattern (only 20-bit and 40-bit internal data widths) > PRBSSEL (101)
•Square wave of 2 UI > PRBSSEL (110)
•Square wave of n UI (Where “n” is internal data width) > PRBSSEL (111)