ERROR CORRECTING DEVICE AND ERROR CORRECTING METHOD

• US 20090222708A1
• Filed: 02/27/2009
• Published: 09/03/2009
• Est. Priority Date: 03/01/2008
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: YAMAGA, Akira
• Granted Patent: US 8,312,348 B2
• Time in Patent Office: Days
• US Class Current: 714/773
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• CPC Class Codes: H03M 13/152 Bose-Chaudhuri-Hocquenghem [BCH] codes
• CPC Class Codes: H03M 13/1545 Determination of error locations, e.g. Chien search or other methods or arrangements for the determination of the roots of the error locator polynomial
• CPC Class Codes: H03M 13/19 Single error correction without using particular properties of the cyclic codes, e.g. Hamming codes, extended or generalised Hamming codes
• CPC Class Codes: H03M 13/2906 using block codes H03M13/2957 takes precedence
• CPC Class Codes: H03M 13/2927 Decoding strategies

Abstract

An error correcting device for correcting erroneous data included in data read out from a nonvolatile memory includes a determining unit that determines whether the data read out from the nonvolatile memory include an error beyond an error correcting capability of the error correcting device. When the determining unit has determined that an error beyond the error correcting capability exists, the error correcting device does not perform the correction of the error.

Claims

1. An error correcting device for correcting erroneous data included in data read out from a nonvolatile memory, the error correcting device comprising a determining unit that determines whether the data read out from the nonvolatile memory include an error beyond an error correcting capability of the error correcting device, wherein

when the determining unit has determined that an error beyond the error correcting capability exists, the error correcting device does not perform the correction of the error.

2. The error correcting device according to claim 1, wherein the determining unit comprises:

a first error number calculating unit that computes an error position polynomial to calculate the number of errors;

a second error number calculating unit that retrieves, in data comprising an error-free area and a correction object area, the data in the correction object area by a Chien search to calculate the number of errors; and

a comparing unit that, when the number of errors calculated by the first error number calculating unit is not equal to the number of errors calculated by the second error number calculating unit, determines that an error beyond the error correcting capability exists.

3. The error correcting device according to claim 1, wherein, upon the retrieval of data comprising an error-free area and a correction object area by a Chien search from the lead of the data, when an error is found in the error-free area,

the determining unit determines that an error beyond the error correcting capability exists.

4. The error correcting device according to claim 2, wherein the error-free area is at least one of a padding area and an area that has been determined to be free from an error.

5. The error correcting device according to claim 1, wherein, in the nonvolatile memory, for data as a writing object, a first error correcting code is generated in blocks, a second error correcting code is generated in a plurality of blocks including the first error correcting code, and the data, the first error correcting code, and the second error correcting code are stored.

6. The error correcting device according to claim 5, further comprising:

a first-error-correction decoding unit that performs first error correction of the data read out from the nonvolatile memory using the first error correcting code; and

a second-error-correction decoding unit that performs the second error correction of the data subjected to the first error correction, wherein

the second error correcting unit functions as the determining unit.

7. The error correcting device according to claim 5, wherein the first error correcting code is a hamming code.

8. The error correcting device according to claim 5, wherein the second error correcting code is a Bose-Chaudhuri-Hocquenghem code or a Reed-Solomon code.

9. The error correcting device according to claim 1, wherein the nonvolatile memory is a NAND-type flash memory.

10. An error correcting method for correcting erroneous data included in data read out from a nonvolatile memory, the error correcting method comprising determining whether the data read out from the nonvolatile memory includes an error beyond an error correcting capability, wherein

when it is determined that the data includes the error beyond the error correcting capability, the error is not corrected.

11. The error correcting method according to claim 10, wherein determining whether the data includes an error beyond an error correcting capability includes

computing a number of errors by calculating an error position polynomial;

computing a number of errors by retrieving a correction object area by a Chien search in data including an error-free area and the correction object area; and

determining that the data includes an error beyond the error correcting capability, when the number of errors calculated by the error position polynomial is not equal to the number of errors calculated by the Chien search.

12. The error correcting method according to claim 11, wherein determining whether the data includes an error beyond an error correcting capability includes

retrieving the data including the error-free area and the correction object area by a Chien search from a lead of the data;

and

determining that the data includes an error beyond the error correcting capability, when an error is found in the error-free area.

13. The error correcting method according to claim 11, wherein the error-free area is at least one of a padding area and an area that has been determined to be free from an error.

14. The error correcting method according to claim 10, wherein the nonvolatile memory is a NAND-type flash memory.