System and method for wear leveling utilizing a relative wear counter

• US 7,876,616 B2
• Filed: 11/12/2007
• Issued: 01/25/2011
• Est. Priority Date: 11/12/2007
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Bhardwaj, Amit, Pierce, Robert, Reid, Robert Alan, Krishnan, Narayanan Vinay
• Primary Examiner(s): Tran; Andrew Q
• Application Number:
  US11/938,725
• Publication Number:
  US 20090122949A1
• Time in Patent Office: 1,170 Days
• Field of Search: 365/185.02, 365/185.09, 365/236, 365/185.11, 365/185.33, 365/185.29
• US Class Current: 365/185.09
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/1044 Space efficiency improvement
• 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

Abstract

An invention is provided for wear leveling in a non-volatile memory system utilizing relative wear counters to indicate relative levels of wear for each memory block in a non-volatile memory system. Whenever a memory block is erased, the associated relative wear counter is incremented. Then, when any relative wear counter reaches a predetermined limit, the value of the lowest relative wear counter is subtracted from each relative wear counter. Thus, each relative wear counter indicates a relative wear level of the associated memory block relative to other memory blocks. In this manner, the relative wear levels are maintained while reducing the amount of memory needed to for each relative wear counter.

Claims

1. A method for providing wear leveling in a non-volatile memory system, the non-volatile memory system including a plurality of memory blocks and a plurality of relative wear counters associated with the memory blocks, comprising the operations of:

incrementing a relative wear counter associated with a memory block when the memory block is erased; and

subtracting a value of a lowest relative wear counter from each relative wear counter when any relative wear counter reaches a predetermined limit.

2. A method as recited in claim 1, wherein each relative wear counter indicates a relative wear level of the associated memory block relative to other memory blocks.

3. A method as recited in claim 1, wherein the predetermined limit is a value equal to the maximum value capable of being stored in a relative wear counter.

4. A method as recited in claim 1, further comprising the operations of:

receiving a request to write data to the non-volatile memory;

searching the plurality of relative wear counters for a relative wear counter storing a lowest value; and

storing the data in the memory block associated with the relative wear counter storing the lowest value.

5. A method as recited in claim 4, wherein the memory block having the lowest value is a free memory block.

6. A method as recited in claim 1, further comprising the operations of:

searching the plurality of relative wear counters for a relative wear counter storing a highest value;

searching the plurality of relative wear counters for a relative wear counter storing a lowest value; and

moving data stored in the memory block associated with the relative wear counter storing the lowest value to the memory block associated with the relative wear counter storing the highest value.

7. A method as recited in claim 6, wherein the relative wear counter having the highest value is associated with a free memory block.

8. A non-volatile memory system, comprising:

a plurality of memory blocks;

a plurality of relative wear counters, each relative wear counter being associated with a particular memory block;

logic that increments a relative wear counter associated with a memory block when the memory block is erased; and

logic that subtracts a value of a lowest relative wear counter from each relative wear counter when any relative wear counter reaches a predetermined limit.

9. A non-volatile memory system as recited in claim 8, wherein each relative wear counter of the plurality of relative wear counters indicates a relative wear level of the associated memory block relative to other memory blocks.

10. A non-volatile memory system as recited in claim 8, wherein the predetermined limit is a value equal to the maximum value capable of being stored in a relative wear counter.

11. A non-volatile memory system as recited in claim 8, further comprising:

logic that searches the plurality of relative wear counters for a relative wear counter storing a lowest value upon receiving a request to write data to the non-volatile memory; and

logic that stores the data in the memory block associated with the relative wear counter storing the lowest value.

12. A non-volatile memory system as recited in claim 11, the relative wear counter storing the lowest value is associated with a free memory block.

13. A non-volatile memory system as recited in claim 8, further comprising:

logic that searches the plurality of relative wear counters for a relative wear counter storing a highest value;

logic that searches the plurality of relative wear counters for a relative wear counter storing a lowest value; and

logic that moves data stored in the memory block associated with the relative wear counter storing the lowest value to the memory block associated with the relative wear counter storing the highest value.

14. A non-volatile memory system as recited in claim 13, further comprising the operation of receiving a request to perform static wear leveling.

15. A non-volatile memory system as recited in claim 13, wherein the relative wear counter storing the highest value is associated with a free memory block.

16. A non-volatile memory system as recited in claim 8, further comprising:

logic that searches the plurality of relative wear counters for a relative wear counter storing a relatively high value;

logic that searches the plurality of relative wear counters for a relative wear counter storing a relatively low value; and

logic that moves data stored in the memory block associated with the relative wear counter storing the relatively low value to the memory block associated with the relative wear counter storing the relatively high value.