Altera Reed-Solomon II MegaCore Function Manual de usuario descargar pdf (Pagina 18)

Figure 3-2: Encoder Timing—One Channel

Shows the timing diagram of the RS II encoder with one channel.

clk_clk

reset_reset_n

in_valid

in_startofpacket

in_endofpacket

in_data[7:0]

in_ready

out_valid

out_startofpacket

out_endofpacket

out_data[7:0]

out_ready

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 236 237 238 239 1 2 3 4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 234235 236 237 238

239

1 114 61 30 244

1 2

The in_startofpacket signal starts a codeword; the in_endofpacket signals its termination. An

asserted in_valid signal indicates valid data. The in_startofpacket signal is only valid when you assert

the in_valid signal. For a 1-channel codeword, assert the in_startofpacket and in_endofpacket

signals for one clock cycle. The encoder uses backpressure by deasserting the in_ready signal when it

receives the in_endofpacket signal. During this time, the encoder signals that it cannot accept more

incoming symbols and generates the check symbols for the current codeword. The IP core does not verify

if the number of symbols (N) exceeds the maximum symbols per codeword. You must ensure that the

codeword sent to the core has a valid N. The reset_reset_n signal is active low and you can assert this

signal asynchronously. However, you have to deassert the reset_reset_n signal synchronously with the

clk_clk signal.

Shortened Codewords

The RS II IP core supports shortened codewords. A shortened codeword contains fewer symbols than the

maximum value of N, which is 2M –1, where N is the total number of symbols per codeword and M is the

number of bits per symbol. A shortened codeword is mathematically equivalent to a maximum-length

code with the extra data symbols at the start of the codeword set to 0. For example, (204,188) is a

shortened codeword of (255,239). Both of these codewords use the same number of check symbols, 16. To

use shortened codewords with the decoder, use the parameter editor to set the codeword length to the

correct value; for the encoder assert endofpacket once it generates enough symbols.

Decoder

When the decoder receives the encoded codeword, it uses the check symbols to detect errors and correct

them.

3-2

Decoder

UG-01090

2015.05.01

Altera Corporation

Reed-Solomon II IP Core Functional Description

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Altera Reed-Solomon II MegaCore Function Manual de usuario Pagina 18

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