Erased sector detection mechanisms

• US 20060133141A1
• Filed: 12/22/2004
• Published: 06/22/2006
• Est. Priority Date: 12/22/2004
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Gorobets, Sergey Anatolievich
• Granted Patent: US 7,437,653 B2
• Time in Patent Office: Days
• US Class Current: 365/185.110
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• CPC Class Codes: G11C 16/16 for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: G11C 16/344 Arrangements for verifying correct erasure or for detecting overerased cells

Abstract

The present invention presents a non-volatile memory and method for its operation that allows instant and accurate detection of erased sectors when the sectors contain a low number of zero bits, due to malfunctioning cells or other problems, and the sector can still be used as the number of corrupted bits is under the ECC correction limit. This method allows the storage system to become tolerant to erased sectors corruption, as such sectors can be used for further data storage if the system can correct this error later in the written data by ECC correction means.

Claims

1. A method of determining whether a unit of data of a memory is erased, comprising:

inverting the data content of the unit of data;

generating a error correction code syndrome for the inverted data content;

performing a data correction on the inverted data content using said syndrome; and

based on the corrected, inverted data content, determining whether the data content of the unit of data was erased.

2. The method of claim 1, wherein said unit of data is a sector of data.

3. The method of claim 1, wherein said inverting the data content includes inverting the associated ECC field.

4. The method of claim 1, wherein the error correction code uses a Reed-Solomon algorithm.

5. The method of claim 1, wherein the error correction code uses a BCH algorithm.

6. The method of claim 1, wherein said method is executed by firmware.

7. The method of claim 1, further comprising:

prior to inverting the data content, performing an initial determination of whether the data content corresponds to an erased state.

8. The method of claim 7, wherein the initial determination is performed in hardware by checking incoming data on a memory bus.

9. The method of claim 1, further comprising:

prior to inverting the data content, determining whether the data unit contains valid, non-erased data.

10. The method of claim 9, wherein said determining whether the data unit contains valid, non-erased data includes:

performing a data correction operation on the content of the data unit.

11. A method of treating a unit of data of a memory, comprising:

quantifying the level of corruption of the content of the unit of data based upon its associated error correction code;

determining whether the level of corruption is acceptable;

in response to determining that the level of corruption is acceptable, correcting the data content; and

based on the corrected data content, determining whether the data content of the unit of data was erased.

12. The method of claim 11, further comprising:

prior to quantifying the level of corruption, generating a error correction code syndrome for the data content, wherein said correcting the data content is performed on the data content and using said syndrome, and wherein the determining whether the data content of the unit of data was erased is based on the corrected data content.

13. The method of claim 12, further comprising:

prior to generating the error correction code syndrome for the data content, inverting the data content of the unit of data, wherein the error correction code syndrome is generated using the data content in inverted form, said correcting the data content is performed on the data content inverted form and using said syndrome, and wherein the determining whether the data content of the unit of data was erased is based on the corrected data content in inverted form.

14. The method of claim 13, wherein said inverting the data content includes inverting the associated ECC field.

15. The method of claim 12, further comprising:

prior to generating the error correction code syndrome for the data content, performing an initial determination of whether the data content corresponds to an erased state.

16. The method of claim 15, wherein the initial determination is performed in hardware by checking incoming data on a memory bus.

17. The method of claim 12, further comprising:

prior to generating the error correction code syndrome for the data content, determining whether the data unit contains valid, non-erased data.

18. The method of claim 17, wherein said determining whether the data unit contains valid, non-erased data includes:

performing a data correction operation on the content of the data unit.

19. The method of claim 11, wherein said unit of data is a sector of data.

20. The method of claim 11, wherein the error correction code uses a Reed-Solomon algorithm.

21. The method of claim 11, wherein the error correction code uses a BCH algorithm.

22. The method of claim 11, wherein said method is executed by firmware.

23. A method of treating a unit of data of a memory, comprising:

determining and quantifying the level of corruption of the content of the unit of data relative to an erased state based upon its associated error correction code; and

determining whether the level of corruption is acceptable.

24. The method of claim 23, further comprising:

in response to determining that the level of corruption is acceptable, correcting the data content.

25. The method of claim 23, further comprising:

prior to determining and quantifying the level of corruption, performing an initial determination of whether the data content corresponds to an erased state.

26. The method of claim 25, wherein the initial determination is performed in hardware by checking incoming data on a memory bus.

27. The method of claim 23, further comprising:

prior to determining and quantifying the level of corruption, determining whether the data unit contains valid, non-erased data.

28. The method of claim 27, wherein said determining whether the data unit contains valid, non-erased data includes:

performing a data correction operation on the content of the data unit.

29. The method of claim 23, wherein said unit of data is a sector of data.

30. The method of claim 23, wherein the error correction code uses a Reed-Solomon algorithm.

31. The method of claim 23, wherein the error correction code uses a BCH algorithm.

32. The method of claim 23, wherein said method is executed by firmware.