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SAS Interface
58 C141-C013
1.4.7 Scrambling
Scrambling is used to reduce the probability of long strings of repeated patterns
appearing on the physical link.
All data dwords are scrambled. Table 1.17 lists the scrambling for different types
of data dwords.
Table 1.17 Scrambling for different data dword types
connection state Data dword type Description of scrambling
SAS idle dword When a connection is not open and there are no
other dwords to transmit, vendor-specific
scrambled data dwords shall be transmitted.
Outside connections
Address frame After an SOAF, all data dwords shall be
scrambled until the EOAF.
SSP frame After an SOF, all data dwords shall be
scrambled until the EOF.
Inside SSP
connection
SSP idle dword When there are no other dwords to transmit,
vendor-specific scrambled data dwords shall be
transmitted.
To generate scrambled values that are to be encoded and transferred on the
physical link layer, dwords to be sent are XOR-ed with the predefined pattern. If
there is no transmission error, the received data of the dwords is XOR-ed with the
same pattern after being decoded so that the dword values of the original data can
be obtained.
The pattern that is XOR-ed with the data dwords is defined by the output of a
linear feedback shift register implemented with the following polynomial:
G(x) = x
16
+ x
15
+ x
13
+ x
4
+ 1
The value of the linear feedback shift register shall be initialized at each SOF and
SOAF to FFFFh.