Systems and methods for data processing with folded parity sector

1. An apparatus for processing data from a non-volatile storage device, comprising:

a decoder configured to iteratively decode codewords in a data block representing a plurality of user data sectors, the codewords comprising user data, folded parity sector data and error correction code parity bits, wherein the folded parity sector data comprises a plurality of parity checks, each comprising a plurality of user data bits from each of the data sectors with an offset between each of the plurality of user data bits from the data sectors determined at least in part by a number of folds in the data sectors; and

a scheduler configured to control decoding of the codewords based at least in part on the folded parity sector data.

2. The apparatus of claim 1 , wherein the data decoder comprises a low density parity check decoder.

3. The apparatus of claim 1 , wherein the scheduler is configured to schedule a plurality of decoding iterations in the decoder for each of the plurality of user data sectors and to schedule an update of the parity sector data based on results of the plurality of decoding iterations.

4. The apparatus of claim 1 , wherein the decoder is configured to decode the codewords according to a parity check matrix for the data block comprising a plurality of component codeword parity check matrices, one for each of the codewords, the parity check matrix for the data block further comprising single parity check bits that satisfy parity check equations in the folded parity sector data, error correction code parity bits for the codewords, and a parity check matrix for the folded parity sector data.

5. The apparatus of claim 4 , wherein the single parity check bits are protected by the error correction code parity bits.

6. The apparatus of claim 1 , wherein the decoder is configured to perform parity sector updates to perform parity checks of bits in the user data specified by the folded parity sector data to generate soft information.

7. The apparatus of claim 6 , wherein the decoder is configured to repeat decoding iterations for the codewords that fail to converge in earlier decoding iterations, wherein the repeated decoding iterations are performed in part based on the soft information.

8. The apparatus of claim 6 , wherein the decoder is configured to perform auxiliary parity sector updates after a subset of the codewords in the data block have been decoded.

9. The apparatus of claim 1 , wherein the decoder comprises memory configured to store carry-on decoding state information.

10. The apparatus of claim 1 , wherein the decoder comprises an irregular low density parity check decoder, and wherein the folded parity sector data parity checks specify different numbers of the user data bits based on column weights.

11. The apparatus of claim 10 , wherein the folded parity sector data parity checks specify the user data bits that bridge high and low column weight portions of combinations of the codewords.

12. The apparatus of claim 1 , wherein the decoder is configured to calculate values of parity bits that have been punctured.

13. The apparatus of claim 12 , wherein the punctured parity bits comprise high column weight parity bits in an irregular low density parity check decoder.

14. The apparatus of claim 1 , wherein the decoder comprises an irregular low density parity check decoder configured to calculate values of high column weight user data bits that have been shortened.

15. The apparatus of claim 1 , wherein the codewords have a plurality of code rates and wherein the scheduler is configured to schedule decoding of the codewords in order of ascending code rates.

16. The apparatus of claim 15 , wherein the folded parity sector data comprises a plurality of layers of parity checks that bridge neighboring codewords in order of ascending code rates.

17. The apparatus of claim 1 , wherein the decoder comprises an irregular low density parity check decoder configured to scale check node to variable node messages based at least in part on column weights.

18. The apparatus of claim 1 , wherein the decoder is configured to apply bit selective scaling to the folded parity sector data.

19. A method of processing data from a non-volatile storage device, comprising:

performing decoding iterations on a plurality of codewords in a data block each associated with a user data sector, wherein the plurality of codewords are protected by a folded parity sector, wherein the folded parity sector specifies parity checks based on multiple bits selected from each of the user data sectors at offsets based in part on a number of folds per user data sector;

performing a parity sector update to generate soft information for the codewords based at least in part on the parity checks specified by the folded parity sector and on the user data sectors; and

repeating the decoding iterations for any of the codewords that failed to converge, based at least in part on the soft information from the parity sector update.

20. A storage system comprising:

a storage medium;

means for decoding codewords in a data block stored on the storage medium, the data block representing a plurality of user data sectors, the codewords comprising user data, folded parity sector data and error correction code parity bits, wherein the folded parity sector data comprises a plurality of parity checks, each comprising a plurality of user data bits from each of the data sectors with an offset between each of the plurality of user data bits from the data sectors determined at least in part by a number of folds in the data sectors; and

means for scheduling decoding of the codewords based at least in part on the folded parity sector data.