By default, spread-spectrum clocking (SSC) is generated by the PS-GTR transmitter for USB 3.0, SATA Gen1, SATA Gen2, SATA Gen 3, and DisplayPort. SSC settings are done by the PCW. For PCIe, SSC generation in the transmitter is turned off because the protocol specification requires SSC to be supported by the reference clock (PS_MGTREFCLK).