Wear leveling method and apparatus for nonvolatile memory

• US 20070208904A1
• Filed: 03/03/2006
• Published: 09/06/2007
• Est. Priority Date: 03/03/2006
• Status: Active Application

• Current Assignee: Sunplus Technology Co., Ltd
• Original Assignee: Sunplus Technology Co., Ltd
• Inventors: Chen, Yuan-Cheng, Hsieh, Wu-Han
• Application Number:
  US11/366,582
• Publication Number:
  US 20070208904A1
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/1036 Life time enhancement
• CPC Class Codes: G06F 2212/7211 Wear leveling
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically
• CPC Class Codes: G11C 29/76 using address translation or modifications

Abstract

A wear leveling apparatus uniformly distributes wear over a nonvolatile memory containing a plurality of memory blocks. The wear leveling apparatus includes a memory unit for storing a record of cold block candidates in the nonvolatile memory and a control unit configured to update the memory unit and release the cold block candidates under a threshold condition. The control unit selects a new memory block to replace one cold block candidate in the memory unit when the cold block candidate is matched with a written address in a write command for the nonvolatile memory. The cold block candidates remained in the memory unit are identified as cold blocks when the nonvolatile memory has been written more than a predetermined write count threshold. The memory blocks with infrequent erasure can be identified and released to uniformly distribute wear over the nonvolatile memory.

Claims

1. A wear leveling method for a nonvolatile memory containing a plurality of memory blocks, the method comprising:

maintaining a record of at least one cold block candidate for the nonvolatile memory; and

moving content in the at least one cold block candidate to at least one free block of the plurality of memory blocks when a threshold condition occurs.

2. The method of claim 1, wherein maintaining the record of at least one cold block candidate further comprises:

initializing the record by selecting at least one memory block of the plurality of memory blocks stored with data from the nonvolatile memory.

3. The method of claim 1, further comprising:

providing a write count for counting a write command number of the nonvolatile memory.

4. The method of claim 3, wherein the threshold condition occurs when the write Count exceeds a predetermined write count threshold.

5. The method of claim 1, wherein the threshold condition occurs when the nonvolatile memory is operated for a predetermined time period.

6. The method of claim 1, further comprising:

updating the record when a written address for the nonvolatile memory is matched with one cold block candidate in the record.

7. The method of claim 6, further comprising:

replacing the matched cold block candidate in the record with a new memory block stored with data in the nonvolatile memory.

8. The method of claim 7, wherein the new memory block is related to the cold block candidate in a predetermined order.

9. The method of claim 8, wherein the new memory block is next to the cold block candidate in a descending order.

10. The method of claim 8, wherein the new memory block is ahead of the cold block candidate in an ascending order.

11. The method of claim 1, further comprising:

reinitializing the record by selecting at least one new cold block candidate after moving the content in the cold block candidate.

12. The method of claim 3, further comprising:

resetting the write count after moving the content in the cold block candidate.

13. In a nonvolatile memory comprising a plurality of memory blocks and characterized with finite erase cycles, a method for identifying infrequently-erased block in the nonvolatile memory comprising:

selecting at least one memory block stored with data as a candidate of infrequently-erased block in the nonvolatile memory;

replacing the candidate with a new memory block when a written address in a write command for the nonvolatile memory is matched with the candidate; and

identifying the candidate as infrequently-erased block when a threshold condition occurs.

14. The method of claim 13, further comprising:

providing a probe index designated to a memory block stored with data and related to the candidate in a predetermined order.

15. The method of claim 14, wherein the new memory block is selected from a memory block designated by the probe index.

16. The method of claim 13, further comprising the step of providing a write count to account for a writing operation number to the nonvolatile memory and the write count is increased by one for each writing operation.

17. The method of claim 16, wherein the threshold condition occurs when the write count exceeds a predetermined write count threshold.

18. The method of claim 13, wherein the threshold condition occurs when the nonvolatile memory is operated for a predetermined time period.

19. A wear leveling apparatus for a nonvolatile memory containing a plurality of memory blocks, the wear leveling apparatus comprising:

a memory unit for storing cold block candidates in a flash memory; and

a control unit configured to select a new memory block to replace one of the cold block candidates with a writing command associated with the cold block candidate and configured to move the content of the cold block candidates to free blocks in the nonvolatile memory in a threshold condition.

20. The apparatus of claim 19, wherein the memory unit comprises a candidate storage to store a physical block addresses of the cold blocks candidates.

21. The apparatus of claim 19, wherein the memory unit comprises a write counter to account for a number of write operation to the nonvolatile memory.

22. The apparatus of claim 19, wherein the memory unit comprises a probe index to indicate a memory block stored with data and closest to the cold block candidates in a descending order.

23. The apparatus of claim 21, wherein the threshold condition is when the nonvolatile memory has been written more than a predetermined write count.

24. The apparatus of claim 23, wherein the control unit comprises a comparator to compare a count result of the write counter with the predetermined write count.

25. The apparatus of claim 19, wherein the control unit is configured to move the content of the candidates to the free blocks in background.