Maintaining an average erase count in a non-volatile storage system

• US 20060149896A1
• Filed: 02/25/2006
• Published: 07/06/2006
• Est. Priority Date: 10/28/2002
• Status: Active Grant

• Current Assignee: Innovative Memory Systems, Inc. (Wi-LAN Inc.)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Qawami, Bahman, Sabet-Sharghi, Farshid, Chang, Robert C.
• Granted Patent: US 7,287,118 B2
• 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 2212/7211 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

Abstract

Methods and apparatus for maintaining an average erase count in a system memory of a non-volatile memory system are disclosed. According to one aspect of the present invention, a method for determining an average number of times each block of a number of blocks within a non-volatile memory of a memory system has been erased includes obtaining an erase count for each block that indicates a number of times each block has been erased. Once all the erase counts have been obtained, the erase counts are summed, and an average erase count that indicates the average number of times each block of the number of blocks has been erased is created by substantially dividing the sum by the number of blocks.

Claims

3-4. -4. (canceled)

5. A non-volatile memory system comprising:

a non-volatile memory, the non-volatile memory including a plurality of blocks, each block including a redundant area for storing overhead data comprising an erase count for that block;

a system memory, comprising a non-volatile memory location for storing a first indicator; and

means for storing, in the first indicator in the system memory, a value corresponding to an average number of times each block included in the plurality of blocks has been erased.

1. The system of claim 5, wherein the system memory further comprises:

a non-volatile memory location for storing a second indicator that indicates a total number of blocks included in the plurality of blocks.

2. The system of claim 1 wherein the system memory further comprises:

a header arranged to contain the first indicator and the second indicator.

8. The non-volatile memory system of claim 5 wherein the non-volatile memory is a NAND flash memory.

6. (canceled)

7. The non-volatile memory system of claim 6 wherein the system memory further comprises an erase count block, for storing an erase count indicator for each of the plurality of blocks.

9. A method of managing a non-volatile memory of a memory system according to an average number of times each block of a number of blocks within the non-volatile memory has been erased, the method comprising:

obtaining an erase count for each block of the number of blocks, the erase count for each block of the number of blocks being arranged to indicate a number of times each block of the number of blocks has been erased, wherein the number of blocks is a total number of usable blocks within the non-volatile memory;

creating a sum of the erase counts for the number of blocks;

creating the average erase count, the average erase count being arranged to indicate the average number of times each block of the number of blocks has been erased, wherein creating the average erase count includes substantially dividing the sum by the number of blocks; and

storing an indicator of the average erase count in a non-volatile portion of a system memory of the memory system.

10. The method of claim 9 wherein the erase count for a first block of the number of blocks is obtained from the first block.

11. The method of claim 10 wherein the erase count for the first block is obtained from a redundant area of the first block.

12. The method of claim 9 wherein the erase count for a first block of the number of blocks is obtained from an erase count block in the non-volatile portion of the system memory, the erase count block being arranged to contain the erase counts for each block of the number of blocks.

13. The method of claim 9 wherein each block of the number of blocks is a usable block.

14. The method of claim 9 wherein the non-volatile memory is a NAND flash memory.

15-21. -21. (canceled)

22. A non-volatile memory system comprising:

a non-volatile memory, the non-volatile memory including a number of blocks, each block including a redundant area for storing overhead data comprising an erase count for that block;

a system memory, associated with the non-volatile memory, and having a non-volatile portion,

means for obtaining an erase count for each block of the number of blocks from the redundant area of each block, the erase count for each block of the number of blocks being arranged to indicate a number of times each block of the number of blocks has been erased;

means for creating a sum of the erase counts for the number of blocks;

means for creating the average erase count, the average erase count being arranged to indicate the average number of times each block of the number of blocks has been erased, wherein the means for creating the average erase count include means for substantially dividing the sum by the number of blocks; and

means for storing a first indicator corresponding to the average erase count in the non-volatile portion of the system memory.

23. (canceled)

24. A non-volatile memory system comprising:

a non-volatile memory including a plurality of blocks, each of the plurality of blocks comprising an overhead portion;

a system memory, associated with the non-volatile memory, and having a non-volatile portion;

means for obtaining an erased block from the plurality of blocks;

means for obtaining, from the non-volatile portion of the system memory, an indicator that characterizes a number of times each block in the plurality of blocks has been erased; and

means for storing the indicator that characterizes a number of times each block in the plurality of blocks has been erased in overhead portion of the erased block as an indication of a number of times the erased block has been erased.

25. The non-volatile memory system of claim 24, wherein the indicator that characterizes a number of times each block in the plurality of blocks has been erased indicates an average, over the plurality of blocks, of the number of times each block of the plurality of blocks has been erased.

26. The memory system of claim 24, wherein the means for obtaining an indicator comprises:

code devices that obtain an erase count for each block of the plurality of blocks, the erase count for each block of the plurality of blocks being arranged to indicate a number of times each block of the plurality of blocks has been erased, wherein the plurality of blocks correspond to blocks within the non-volatile memory;

code devices that create a sum of the erase counts for the plurality of blocks;

code devices that create the average erase count, the average erase count being arranged to indicate the average number of times each memory element of the plurality of blocks has been erased, wherein the code devices that create the average erase count include code devices that substantially divide the sum by the number of blocks in the plurality of blocks; and

a memory area that stores the code devices.

28. The memory system of claim 26 wherein the erase count for a first block of the plurality of blocks is obtained from one of the first block and an erase count block arranged to contain the erase counts for each block of the plurality of blocks.

30. The memory system of claim 26 wherein the non-volatile memory is a NAND flash memory.

27. (canceled)

29. (canceled)

31-40. -40. (canceled)