Patent ID: 6941502

Claim:
Apparatus for detecting and/or correcting data encoded into first and second codewords using a first error correction code and second error correction code, respectively, each of said first d second error correction codes having a predetermined error and/or erasure detecting an r correcting capability relayed to the numbers of errors, of unknown location, and erasures, of known location, that can corrected in a respective first or second codeword, each of the codewords comprising a respective predetermined number of symbols or elements, said apparatus comprising: a first error detecting and/or correcting stage arranged to receive a stream of first codewords and to apply error detection and/or correction to errors and/or erasures in said first codewords; a second error detecting and/or correcting stage for receiving second codewords derived from the output from said first error detecting and/or correcting stage and applying error detection and/or correction to errors and/or erasures in said second codewords, wherein, for each first codeword, said first error detecting and/or correcting stage outputs to said second error detecting and/or correcting stage data indicative of an error state depends on the error detecting and/or correcting capability of said first error correction code and the number of actual errors an erasures corrected in said first codeword, said error state being one of at least three possible states comprising a “bad” state indicating that the codeword is bad, at least one “intermediate” state indicating that the codeword is of intermediate quality, and a “good” state indicating that the codeword is good, and said second error detecting and/or correcting stage is operable to use the data indicative of said error state provided by said first error detecting and/or correcting stage to identify, as being of an intermediate state, selected symbols or elements in said second codewords which are derived from a first codeword indicated as having an intermediate state.