VS1005g Datasheet
10 VS1005 PERIPHERALS AND REGISTERS
10.10.2 Reed-Solomon Codec
Vs1005 has a Reed-Solomon encoder and decoder for error correction e.g. from nand flash
data. Reed Solomon is a forward error correction code which adds redundancy at the end of
the message. The code word length n is defined as k + 2*t where k is the maximum number of
data symbols (pay load) and 2*t is the number of parity check symbols. The algorithm can fix
up to t symbols from code word and detect 2*t errors.
The Reed Solomon codec in vs1005 supports two different code lengths
• NF: n = 1023 symbols and t = 4. This makes 2*t = 8 10-bit parity check symbols. The
data symbols are interpreted as 8-bit symbols where the two msb bits are always zero.
• RF: n = 255 symbols and t = 16. This makes 2*t = 32 8-bit parity check symbols. Also the
data symbols are 8 bits wide.
vs1005 Reed Solomon Codecs
Codec Data Symbols (k) Symbol Width Check Symbols (2*t) Typical Code Width (n)
NF
RF
<= 1015
<= 223
8 / 10 bits
8 bits
8 (10 bits)
32 (8 bits)
518 + 8
223 + 32
The NF codec is used for multi level cell (MLC) flash error detection and correction. Therefore
the symbol width is limited to 8 bits for data symbols. The R-S encoder generates eight 10-bit
parity check symbols (80 bits) which are stored with 518-byte user data. These check symbols
are organized as 10 8-bit symbols which are stored to memory chip. The code word would
therefore be a total of 528 bytes long.
NF Reed Solomon encoder check symbols are outputed as five 16-bit words (80 bits total).
These check symbol words can be read from RS_DATA port when the RS encoder has finished
calculation. The check symbol organization is as listed in the table.
NF Reed Solomon Encoder Check Symbol Organization
Check Symbol
RS Encoder output word bits
0
1
2
3
4
5
6
7
word[0](1:0)
word[1](11:8) &
word[1](5:0)
word[2](15:8) &
&
word[0](15:8)
word[0](7:2)
word[1](15:12)
word[1](7:6)
word[2](7:0)
word[3](15:10)
word[3](7:4)
&
word[3](9:8)
word[3](3:0)
&
&
word[4](13:8) &
word[4](7:0)
&
word[4](15:14)
RF Reed Solomon encoder outputs the 8-bit check symbols as 16 16-bit words. Here the 32
8-bit symbols are organized in big endian format. This codec provides a means to detect 32
symbo errors and to fix 16 symbols.
The NF Reed Solomon decoder makes it possible to detect 8 symbol errors and to fix a maxi-
mum of 4 symbols. The decoder first reads the data symbols and then the parity check words.
Version: 0.2, 2012-03-16
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ETC [ ETC ]
