Method and apparatus for managing an erase count block

• US 7,103,732 B1
• Filed: 10/28/2002
• Issued: 09/05/2006
• Est. Priority Date: 10/28/2002
• Status: Expired due to Term

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Qawami, Bahman, Sabet-Sharghi, Farshid, Chang, Robert C.
• Primary Examiner(s): NGUYEN, THAN VINH
• Application Number:
  US10/281,626
• Time in Patent Office: 1,408 Days
• Field of Search: 711/103, 711154-156, 711170-173, 365/185.33, 365/230.03
• US Class Current: 711/156
• 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

Abstract

Methods and apparatus for managing erase counts in a non-volatile memory system. According to one aspect of the present invention, a method for initializing an erase count block in a system memory of a non-volatile memory system, the non-volatile memory system which includes a non-volatile memory involves allocating a plurality of pages within the system memory that are divided into a plurality of entries. Each entry of the plurality of entries has an associated block in the non-volatile memory. The method also includes identifying usable blocks which are suitable for use in accepting user data, and storing values in each entry which is associated with a usable block. Storing the values in each entry which is associated with a usable block substantially identifies the usable block as being usable.

Claims

1. A method for initializing an erase count block in a system memory of a non-volatile memory system, the non-volatile memory system including a non-volatile memory arranged as a plurality of blocks, and also including the system memory, the method comprising:

allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

examining the plurality of blocks to identify-usable blocks that may be written to or read from, and to identify unusable blocks;

for each of the identified usable blocks, storing, in the associated entry of the plurality of entries for that block, a value indicating a number of times that the identified usable block has been erased;

for each of the identified unusable blocks, storing, in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

allocating a header within the system memory, the header being associated with the plurality of pages; and

storing a second value in the header, wherein the second value is arranged to indicate an average number of times each usable block of the plurality of blocks has been erased.

2. The method of claim 1 wherein the value indicating a number of times that the identified usable block has been erased is an erase count associated with the identified usable block.

3. The method of claim 1, wherein the indicator indicating that the identified unusable block is unusable corresponds to a maximum value erase count.

4. A method for initializing an erase count block in a system memory of a non-volatile memory system, the non-volatile memory system including a non-volatile memory arranged as a plurality of blocks, and also including the system memory, the method comprising:

allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

examining the plurality of blocks to identify-usable blocks that may be written to or read from, and to identify unusable blocks;

for each of the identified usable blocks, storing, in the associated entry of the plurality of entries for that block, an erase count associated with the identified usable block;

for each of the identified unusable blocks, storing, in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

determining an average value by substantially averaging the erase counts; and

storing the average value in a first page, the first page being associated with the plurality of pages.

5. The method of claim 4 wherein the non-volatile memory is a NAND flash memory.

6. A memory system comprising:

a system memory;

a non-volatile memory, arranged as a plurality of blocks;

code devices for allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

code devices for examining the plurality of blocks to identify-usable blocks that may be written to or read from, and to identify unusable blocks;

code devices for storing, for each of the identified usable blocks, in the associated entry of the plurality of entries for that block, a value indicating a number of times that the identified usable block has been erased, and for storing, for each of the identified unusable blocks and in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

code devices for allocating a header within the system memory, the header being associated with the plurality of pages;

code devices for storing a second value in the header, wherein the second value is arranged to indicate an average number of times each usable block of the plurality of blocks has been erased; and

a memory area for storing the code devices.

7. The memory system of claim 6 wherein the value indicating a number of times that the identified usable block has been erased is an erase count associated with the identified usable block.

8. The memory system of claim 6, wherein the indicator indicating that the identified unusable block is unusable corresponds to a maximum value erase count.

9. The memory system of claim 6 wherein the code devices are one of firmware code devices and software code devices.

10. The memory system of claim 6 wherein the non-volatile memory is a NAND flash memory.

11. A memory system comprising:

a system memory;

a non-volatile memory, arranged as a plurality of blocks;

code devices for allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

code devices for examining the plurality of blocks to identify-usable blocks that may be written to or read from, and to identify unusable blocks;

code devices for storing, for each of the identified usable blocks, in the associated entry of the plurality of entries for that block, a value indicating a number of times that the identified usable block has been erased, and for storing, for each of the identified unusable blocks and in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

code devices for determining an average value by substantially averaging the erase counts;

code devices storing the average value in a first page, the first page being associated with the plurality of pages; and

a memory area for storing the code devices.

12. The memory system of claim 11 wherein the code devices are one of firmware code devices and software code devices.

13. The memory system of claim 11 wherein the non-volatile memory is a NAND flash memory.

14. The memory system of claim 11, wherein the indicator indicating that the identified unusable block is unusable corresponds to a maximum value erase count.

15. A method for processing an erased block associated with a non-volatile memory of a memory system, the non-volatile memory including a plurality of blocks, the method comprising:

obtaining the erased block;

identifying a first entry in an erase count block that corresponds to the erased block, wherein the erase count block is stored in a system memory of the non-volatile memory;

determining when the first entry is an indication of a number of times the erased block has been erased; and

substantially copying the first entry into the erased block when it is determined that the first entry is an indication of a number of times the erased block has been erased.

16. The method of claim 15 further including:

substantially copying a second entry into the erased block when it is determined that the first entry is not an indication of the number of times the erased block has been erased, the second entry being stored in the system memory, wherein the second entry is arranged to indicate an average number of times the plurality of block has been erased.

17. The method of claim 16 wherein the second entry is stored in the erase count block.

18. The method of claim 15 wherein substantially copying the first entry into the erased block includes copying the first entry into an overhead area of the erased block.

19. A memory system comprising:

a non-volatile memory, the non-volatile including a plurality of blocks, wherein the plurality of blocks includes an erased block;

a system memory;

code devices for obtaining the erased block;

code devices identifying a first entry in an erase count block that corresponds to the erased block, wherein the erase count block is stored in the system memory;

code devices for determining when the first entry is an indication of a number of times the erased block has been erased;

code devices for substantially copying the first entry into the erased block when it is determined that the first entry is an indication of a number of times the erased block has been erased; and

a memory area that stores the code devices.

20. The memory system of claim 19 further including:

code devices for substantially copying a second entry into the erased block when it is determined that the first entry is not an indication of the number of times the erased block has been erased, the second entry being stored in the erase count block, wherein the second entry is arranged to indicate an average number of times the plurality of blocks has been erased.

21. The memory system of claim 19 wherein the code devise substantially copying the first entry into the erased block include code devices for copying the first entry into an overhead area of the erased block.

22. The memory system of claim 19 wherein the code devices are one of firmware code devices and software code devices.

23. A method for updating a first entry within an erase count block of a system memory of a non-volatile memory, the erase count block including a plurality of pages, each page of the plurality of pages including a plurality of entries, wherein the first entry is included in the plurality of entries, the method comprising:

identifying a block, the block being stored in a non-volatile memory;

determining when the block is usable;

setting bits in the first entry to indicate that the block is not usable when it is determined that the block is unusable;

determining when the block is unerased when it is determined that the block is usable;

reading bits stored in the block when it is determined that the block is unerased, the bits being arranged to indicate a number of times the block has been erased; and

setting the bits in the first entry to correspond to the bits stored in the block when it is determined that the block is unerased.

24. The method of claim 23 further included:

reading the bits in the first entry; and

determining when the bits in the first entry do not substantially correspond to the bits stored in the block, wherein when it is determined that the bits in the first entry do not substantially correspond to the bits stored in the block, the bits in the first entry are set to correspond to the bits stored in the block.

25. The method of claim 23 wherein determining when the block is usable includes determining when the block has a growing defect, and wherein setting the bits in the first entry to indicate that the block is not usable includes setting the bits in the first entry to indicate that the block has a growing defect.

26. A memory system comprising:

a system memory, the system memory including an erase count block, the erase count block including a plurality of pages, each page of the plurality of pages including a plurality of entries, wherein the first entry is included in the plurality of entries;

a non-volatile memory;

code devices for identifying a block, the block being stored in the non-volatile memory;

code devices for determining when the block is usable;

code devices for setting bits in the first entry to indicate that the block is not usable when it is determined that the block is unusable;

code devices for determining when the block is unerased when it is determined that the block is usable;

code devices for reading bits stored in the block when it is determined that the block is unerased, the bits being arranged to indicate a number of times the block has been erased;

code devices for setting the bits in the first entry to correspond to the bits stored in the block when it is determined that the block is unerased; and

a memory area that stores the code devices.

27. The memory system of claim 26 further including:

code devices for reading the bits in the first entry; and

code devices for determining when the bits in the first entry do not substantially correspond to the bits stored in the block, wherein when it is determined that the bits in the first entry do not substantially correspond to the bits stored in the block, the bits in the first entry are set to correspond to the bits stored in the block.

28. The memory system of claim 26 wherein the code devices for determining when the block is usable include code devices for determining when the block has a growing defect, and wherein the code devices for setting the bits in the first entry to indicate that the block is not usable include code devices for setting the bits in the first entry to indicate that the block has a growing defect.

29. A method for processing a first block associated with a non-volatile memory of a memory system, the non-volatile memory including a plurality of blocks, the method comprising:

determining when the first block is usable;

reading bits of the first block when it is determined that the first block is usable, the bits being arranged to indicate a number of times the first block has been erased;

identifying a first entry in an erase count block that corresponds to the first block, wherein the erase count block is stored in a system memory of the memory system;

determining when the bits of the first block have a value that is less than a value of the first entry; and

substantially copying the first entry into the bits of the first block when it is determined that bits of the first block have a value that is less than the value of the first entry.

30. The method of claim 29 further including:

updating the first entry to indicate that the first block is not usable when it is determined that the first block is not usable.

31. The method of claim 30 wherein updating the first entry to indicate that the first block is not usable includes updating the first entry to indicate that the first block has a growing defect.

32. The method of claim 29 wherein the bits of the first block are located in a redundant area of the first block.

33. The method of claim 32 wherein the bits of the first block are an erase count of the first block.

34. A memory system comprising:

a non-volatile memory including a plurality of blocks, the plurality of blocks including a first block;

a system memory, the system memory including an erase count block, the erase count block including a plurality of pages, the plurality of pages being substantially divided into a plurality of entries;

code devices for determining when the first block is usable;

code devices for reading bits of the first block when it is determined that the first block is usable, the bits being arranged to indicate a number of times the first block has been erased;

code devices for identifying a first entry in the erase count block that corresponds to the first block;

code devices for determining when the bits of the first block have a value that is less than a value of the first entry;

code devices for substantially copying the first entry into the bits of the first block when it is determined that bits of the first block have a value that is less than the value of the first entry; and

a memory area that stores the code devices.

35. The memory system of claim 34 further including:

code devices for updating the first entry to indicate that the first block is not usable when it is determined that the first block is not usable, wherein the code devices for updating the first entry to indicate that the first block is not usable include code devices for updating the first entry to indicate that the first block has a growing defect.

36. The memory system of claim 34 wherein the bits of the first block are located in a redundant area of the first block.

37. A memory system comprising:

a system memory;

a non-volatile memory, arranged as a plurality of blocks,

means for allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

means for examining the plurality of blocks to identify usable blocks that may be written to or read from, and to identify unusable blocks;

means for storing, for each of the identified usable blocks, in the associated entry of the plurality of entries for that block, a value indicating a number of times that the identified usable block has been erased, and for storing, for each of the identified unusable blocks, storing, in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

means for allocating a header within the system memory, the header being associated with the plurality of pages; and

means for storing a second value in the header, wherein the second value is arranged to indicate an average number of times each usable block of the plurality of blocks has been erased.

38. The memory system of claim 37 wherein the value indicating a number of times that the identified usable block has been erased is an erase count associated with the identified usable block.

39. The memory system of claim 37 wherein the non-volatile memory is a NAND flash memory.

40. The memory system of claim 37, wherein the indicator indicating that the identified unusable block is unusable corresponds to a maximum value erase count.

41. A memory system comprising:

a system memory;

a non-volatile memory, arranged as a plurality of blocks;

means for allocating a plurality of pages within the system memory, wherein each of the plurality of pages comprises a plurality of entries, each entry of the plurality of entries being associated with a corresponding block of the plurality of blocks in the non-volatile memory;

means for examining the plurality of blocks to identify usable blocks that may be written to or read from, and to identify unusable blocks; and

means for storing, for each of the identified usable blocks, in the associated entry of the plurality of entries for that block, an erase count associated with the identified usable block, and for storing, for each of the identified unusable blocks, storing, in the associated entry of the plurality of entries for that block, an indicator indicating that the identified unusable block is unusable;

means for determining an average value by substantially averaging the erase counts; and

means for storing the average value in a first page, the first page being associated with the plurality of pages.

42. The memory system of claim 41 wherein the non-volatile memory is a NAND flash memory.

43. The memory system of claim 41, wherein the indicator indicating that the identified unusable block is unusable corresponds to a maximum value erase count.