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The scrambler randomizes data to create transitions to DC-balance the signal and help CDR circuits. The scrambler uses a x58 + x39 +1 polynomial and supports both synchronous scrambling used for Interlaken and asynchronous (also called self-synchronized) scrambling used for the 10GBASE-R protocol.
The asynchronous (self-synchronizing) mode does not require an initialization seed. Except for the two sync header bits in each 66-bit data block, the entire 64-bit payload is scrambled by feeding it into a linear feedback shift register (LFSR) continuously to generate scrambled data while the sync-header bits bypass the scrambler. The initial seed is set to all 1s. You can change the seed for the 10GBASE-R protocol using the Native PHY IP Parameter Editor.
In synchronous mode, the scrambler is initially reset to different programmable seeds on each lane. The scrambler then runs by itself. Its current state is XOR’d with the data to generate scrambled data. A data checker in the scrambler monitors the data to determine if it should be scrambled or not. If a synchronization word is found, it is transmitted without scrambling. If a Scrambler State Word is detected, the current scramble state is written into the 58-bit scramble state field in the Scrambler State Word and sent over the link. The receiver uses this scramble state to synchronize the descrambler. The seed is automatically set for Interlaken protocol.
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