RSDEC-DBLK-XM-U3 Lattice, RSDEC-DBLK-XM-U3 Datasheet - Page 13

• Manufacturer Part Number: RSDEC-DBLK-XM-U3
• Description: Encoders, Decoders, Multiplexers & Demultiplexers Dynamic Block Reed Solomon Decoder
• Manufacturer: Lattice

Specifications of RSDEC-DBLK-XM-U3

• Factory Pack Quantity: 1

Lattice Semiconductor
IPUG52_01.6, December 2010
where:
The following sections describe the function of each block of the RS Decoder.
Syndrome Transform
The Syndrome Transform (also called Syndrome Generation) block evaluates the received codeword of the gener-
ator polynomial. If the received data contains an error, the syndrome polynomial generated will be non-zero. If the
received data has no error, the syndrome polynomial is zero, and the data is passed out of the decoder without any
error correction.
Key Equation Solver
This is the heart of the RS Decoder. This block generates the Error Locator polynomial (x) (also known as the
“Key Equation” as it is the key to solve the decoding problem). After the Error Locator polynomial has been deter-
mined, it is used to compute the Error Evaluator polynomial ¾(x)
Error Locator
This block is implemented using the Chien-search method. Essentially, this method evaluates the Error Locator
polynomial at all the elements in the Galois Field. The Error Locator polynomial evaluates to zero at its roots. The
Chien-search takes up to m cycles, where m is the number of elements in the Galois Field, to determine all the
roots. If the roots are determined before m cycles are over, the search is terminated early.
Error Magnitude Corrector
Once the location of the error has been determined, the Error Magnitude Corrector evaluates the evaluator polyno-
mial at that root. It uses the result to calculate the value of the error at the given location. Once this has been deter-
mined, the value is added to the received word to recover the original data. The addition occurs only when the Error
Locator polynomial evaluates to zero.
Control Unit
The control unit handles the interface, pipelining and handshaking communication between the various blocks and
the I/O ports. The control circuit moves the data without processing it through the decoder when no error is
detected. Similarly, when the number of errors exceeds the maximum range of correction, the control circuit stops
all data processing activities. The control circuit interacts with the other blocks to generate the status signals like
obstart, obend, outvalid, rfib, errfnd, errcnt, erscnt and fail. Once the block has been processed,
the control circuit sends out the rfi signal to the output to start the processing of the next data block.
Basis Conversion Modules
When core configuration is selected as CCSDS, then two additional Basis Conversion modules are added to the
RS Decoder. These modules comply with the CCSDS specification. Dual-basis to normal polynomial-basis conver-
sion module is added after the din input port and normal polynomial-basis to dual-basis conversion module is
added before the dout output port.
Variable Block Size
In the constant Block size type option, the block size value and number of information symbols are provided
as constant values through the RS Decoder GUI before core generation. For variable Block size type option,
the block size value is provided dynamically through the input port blocksize. The number of the information
symbols is calculated from the block size value provided through the input port and the number of check symbols.
The number of check symbols can be either constant and defined in the GUI or variable and given through the
S(x)(x) = ¾(x) mod x
¾(x) is the Error Evaluator polynomial.
2t is the number of check symbols introduced in the encoder.
2t
13 Dynamic Block Reed-Solomon Decoder User’s Guide
Functional Description