Method and system for determining soft information offsets

• US 9,647,697 B2
• Filed: 12/10/2015
• Issued: 05/09/2017
• Est. Priority Date: 03/16/2015
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Inventors: Chen, Xiaoheng, Kang, Jingyu, Zhu, Jiangli, Tai, Ying Yu
• Primary Examiner(s): Tu, Christine
• Application Number:
  US14/965,578
• Publication Number:
  US 20160274969A1
• Time in Patent Office: 516 Days
• CPC Class Codes: G06F 11/1012 using codes or arrangements adapted for a specific type of error G06F11/1048 takes precedence
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 2029/0411 Online error correction
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: G11C 29/52 Protection of memory contents; Detection of errors in memory contents
• CPC Class Codes: H03M 13/1111 Soft-decision decoding, e.g. by means of message passing or belief propagation algorithms
• CPC Class Codes: H03M 13/1515 Reed-Solomon codes
• CPC Class Codes: H03M 13/152 Bose-Chaudhuri-Hocquenghem [BCH] codes
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3723 using means or methods for the initialisation of the decoder
• CPC Class Codes: H03M 13/3746 with iterative decoding
• CPC Class Codes: H03M 13/45 Soft decoding, i.e. using symbol reliability information H03M13/41 takes precedence
• CPC Class Codes: H03M 13/6325 Error control coding in combination with demodulation

Abstract

Systems, methods, and/or devices are used to improve decoding of data read from a storage device with one or more memory devices. In one aspect, the method includes obtaining, in response to a read request, a codeword with two or more codeword portions from distinct memory portions of the storage device. When a decoding iteration on the codeword fails to satisfy predetermined decoding criteria, the method includes, for the two or more codeword portions of the codeword: determining a bit-flip count between raw read data for a respective codeword portion and a decoding result for the respective codeword portion after the decoding iteration; determining a soft information offset for the respective codeword portion based on the bit-flip count for the respective codeword portion relative to bit-flips counts for other codeword portions; and adjusting soft information for the respective codeword portion based on the soft information offset.

Claims

1. A method of improving decoding of data read from a storage device with one or more memory devices, the method comprising:

at a storage controller with one or more processors and memory;

in response to a read request, obtaining a codeword with two or more codeword portions from the storage device, wherein the two or more codeword portions at least include a first codeword portion with first raw read data from a first memory portion of the storage device and a second codeword portion with second raw read data from a second memory portion of the storage device distinct from the first memory portion;

performing a first decoding iteration on the codeword; and

in accordance with a determination that the first decoding iteration fails to satisfy one or more predetermined decoding criteria;

for the two or more codeword portions of the codeword;

determining a count of bit-flips between the raw read data for a respective codeword portion of the two or more codeword portions and a decoding result for the respective codeword portion after the first decoding iteration;

determining a soft information offset for the respective codeword portion based on the determined count of bit-flips for the respective codeword portion relative to bit-flips counts for other codeword portions of the codeword; and

adjusting soft information for the respective codeword portion based on the determined soft information offset.

2. The method of claim 1, wherein performing the first decoding iteration on the codeword includes:

obtaining soft information for the two or more codeword portions so as to generate a soft information codeword; and

performing the first decoding iteration on the soft information codeword.

3. The method of claim 2, wherein the soft information for the two or more codeword portions is generated based on a look-up table that associates log-likelihood ratio (LLR) values with memory portions of the storage device.

4. The method of claim 3, further comprising:

storing the soft information offset determined after the first decoding iteration, wherein the soft information offset is associated with an entry in the look-up table for a memory portion in the storage device that corresponds to the respective codeword portion.

5. The method of claim 1, wherein the first decoding iteration is a first iteration of a low-density parity check (LDPC) decoding process.

6. The method of claim 1, wherein the first memory portion is located in a first die in the storage device, and

wherein the second memory portion is located in a second die in the storage device distinct from the first die.

7. The method of claim 1, wherein the soft information offset for the respective codeword portion decreases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is greater than the bit-flips counts for the other codeword portions of the codeword, and

wherein the soft information offset for the respective codeword portion increases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is less than the bit-flips counts for the other codeword portions of the codeword.

8. The method of claim 1, wherein the soft information offset for the respective codeword portion increases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is greater than the bit-flips counts for the other codeword portions of the codeword, and

wherein the soft information offset for the respective codeword portion decreases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is less than the bit-flips counts for the other codeword portions of the codeword.

9. The method of claim 1, further comprising:

after adjusting the soft information for the two or more codeword portions of the codeword, performing a second decoding iteration on the soft information codeword; and

in accordance with a determination that the second decoding iteration fails to satisfy the one or more predetermined decoding criteria;

for the two or more codeword portions of the codeword;

determining a second count of bit-flips between the raw read data for a respective codeword portion of the two or more codeword portions and a second decoding result for the respective codeword portion after the second decoding iteration;

determining a second soft information offset based on the determined second count of bit-flips for the respective codeword portion relative to bit-flips counts for the other codeword portions of the codeword; and

adjusting the soft information for the respective codeword portion based on the determined second soft information offset.

10. The method of claim 1, wherein the storage device comprises one or more flash memory devices.

11. A storage device, comprising:

non-volatile storage for storing information; and

a storage controller having one or more processors configured to execute instructions in one or more programs, wherein the storage controller is configured to perform operations comprising;

in response to a read request, obtaining a codeword with two or more codeword portions from the storage device, wherein the two or more codeword portions at least include a first codeword portion with first raw read data from a first memory portion of the storage device'"'"'s non-volatile storage and a second codeword portion with second raw read data from a second memory portion of the storage device'"'"'s non-volatile storage distinct from the first memory portion;

performing a first decoding iteration on the codeword; and

in accordance with a determination that the first decoding iteration fails to satisfy one or more predetermined decoding criteria;

for the two or more codeword portions of the codeword;

determining a count of bit-flips between the raw read data for a respective codeword portion of the two or more codeword portions and a decoding result for the respective codeword portion after the first decoding iteration;

determining a soft information offset for the respective codeword portion based on the determined count of bit-flips for the respective codeword portion relative to bit-flips counts for other codeword portions of the codeword; and

adjusting soft information for the respective codeword portion based on the determined soft information offset.

12. The storage device of claim 11, wherein the storage controller includes a decoding determination module for determining the decoding result.

13. The storage device of claim 11, wherein the storage controller includes an offset determining module for determining the soft information offset.

14. The storage device of claim 11, wherein the storage controller includes a soft information adjusting module for adjusting the soft information for the respective codeword portion.

15. The storage device of claim 11, wherein performing the first decoding iteration on the codeword includes:

obtaining soft information for the two or more codeword portions so as to generate a soft information codeword; and

performing the first decoding iteration on the soft information codeword.

16. The storage device of claim 15, wherein the soft information for the two or more codeword portions is generated based on a look-up table that associates log-likelihood ratio (LLR) values with memory portions of the storage device.

17. The storage device of claim 16, wherein the storage controller is further configured to perform operations comprising:

storing the soft information offset determined after the first decoding iteration, wherein the soft information offset is associated with an entry in the look-up table for a memory portion in the storage device that corresponds to the respective codeword portion.

18. The storage device of claim 11, wherein the first decoding iteration is a first iteration of a low-density parity check (LDPC) decoding process.

19. The storage device of claim 11, wherein the first memory portion is located in a first die in the storage device, and

wherein the second memory portion is located in a second die in the storage device distinct from the first die.

20. The storage device of claim 11, wherein the soft information offset for the respective codeword portion decreases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is greater than the bit-flips counts for the other codeword portions of the codeword, and

wherein the soft information offset for the respective codeword portion increases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is less than the bit-flips counts for the other codeword portions of the codeword.

21. The storage device of claim 11, the soft information offset for the respective codeword portion increases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is greater than the bit-flips counts for the other codeword portions of the codeword, and

wherein the soft information offset for the respective codeword portion decreases the magnitude of the soft information for the respective codeword portion in accordance with a determination that the count of bit-flips for the respective codeword portion is less than the bit-flips counts for the other codeword portions of the codeword.

22. The storage device of claim 11, wherein the storage controller is further configured to perform operations comprising:

after adjusting the soft information for the two or more codeword portions of the codeword, performing a second decoding iteration on the soft information codeword; and

in accordance with a determination that the second decoding iteration fails to satisfy the one or more predetermined decoding criteria;

for the two or more codeword portions of the codeword;

determining a second count of bit-flips between the raw read data for a respective codeword portion of the two or more codeword portions and a second decoding result for the respective codeword portion after the second decoding iteration;

determining a second soft information offset based on the determined second count of bit-flips for the respective codeword portion relative to bit-flips counts for the other codeword portions of the codeword; and

adjusting the soft information for the respective codeword portion based on the determined second soft information offset.

23. A non-transitory computer readable storage medium, storing one or more programs configured for execution by one or more processors of a storage device, the one or more programs including instructions for performing operations comprising:

in response to a read request, obtaining a codeword with two or more codeword portions from the storage device, wherein the two or more codeword portions at least include a first codeword portion with first raw read data from a first memory portion of the storage device and a second codeword portion with second raw read data from a second memory portion of the storage device distinct from the first memory portion;

performing a first decoding iteration on the codeword; and

in accordance with a determination that the first decoding iteration fails to satisfy one or more predetermined decoding criteria;

for the two or more codeword portions of the codeword;

determining a count of bit-flips between the raw read data for a respective codeword portion of the two or more codeword portions and a decoding result for the respective codeword portion after the first decoding iteration;

determining a soft information offset for the respective codeword portion based on the determined count of bit-flips for the respective codeword portion relative to bit-flips counts for other codeword portions of the codeword; and

adjusting soft information for the respective codeword portion based on the determined soft information offset.