Altera Reed-Solomon Compiler - Manual (Page 23)

Chapter 3: Functional Description 3–5
RS Decoder
December 2014 Altera Corporation Reed-Solomon Compiler
User Guide
The RS decoder observes Avalon-ST interface standard for input and output data. One
clock cycle after the decoder asserts sink_ena, you can assert sink_val. The decoder
accepts the data at rsin as valid data. The codeword is started with sink_sop. The
numcheck
and numn signals are latched to sink_sop.
The codeword is finished when sink_eop is asserted. If sink_ena is de-asserted, from
one clock cycle onwards the decoder cannot process any more data until sink_ena is
asserted again.
At the output the operation is identical. If you assert source_ena, the decoder asserts
source_val
and provides valid data on rsout if available. Also, it indicates the start
and end of the codeword with source_sop and source_eop respectively.
Figure 3–4 shows the operation of the RS decoder.
The decoder has the following optional outputs, which you turn on in IP Toolbench:
■ Error symbol
■ Bit error count
Error Symbol Output
The error symbol output, rserr is the Galois field error correction value. The RS
decoder finds the error values and location and adds these values in the Galois field to
the input value. Galois field addition and subtraction is the same operation. An XOR
operation performs this operation between bits of the two values.
Figure 3–4. Decoder Timing
clk
sink_ena
sink_val
sink_sop
sink_eop
rsin[8:1]
source_ena
source_val
source_sop
source_eop
rsout[8:1]
numcheck[4:1]
numn[4:1]
01 02 03 04 05 06 07 08 P1 P2 P3 P4 P5 09 10 11 12 13
01 02 03 04 05 06 07 08 P1 P2 P3 P4 P5 12
05 05
13 13