SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The contents of a frame are scrambled before being passed to the link 8b/10b encoder. Scrambling is performed on Dword quantities by XORing the data to be transmitted with the output of a linear feedback shift register (LFSR). All data words between the SOFp and EOFp are scrambled, including the CRC. Figure 24-155 shows the basic flow.
The SATA controller (as defined by the SATA standard) performs scrambling/descrambling processing for EMI reduction purposes. Two scramblers are instantiated within the SATA controller: The first, the data payload scrambler, scrambles FIS data payload contents (including the calculated CRC Dword); the second, the repeated primitive suppression scrambler, scrambles only the repeated primitive stream contents.
The scrambling runs as follows: A certain data payload Dword located between SOFp and EOFp is XORed with the data payload scrambler output. The resulting scrambled Dword is submitted to the 8b/10b encoder for transmission.
On reception, the Dword is decoded using a 10b/8b decoder, the scrambler output is XORed with the resulting Dword, and the resulting Dword is presented to the link layer. It is then used for CRC computation. The CRC Dword is scrambled in the same way as data payload characters.
For details on the scrambling/descrambling feature, see the SATA Standard Specification (rev.2.6).