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

• US 7,035,967 B2
• Filed: 10/28/2002
• Issued: 04/25/2006
• Est. Priority Date: 10/28/2002
• Status: Expired due to Term

• 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.
• Primary Examiner(s): Vital, Pierre M.
• Application Number:
  US10/281,823
• Publication Number:
  US 20040177212A1
• Time in Patent Office: 1,275 Days
• Field of Search: 365/185.29, 365/185.33, 365/230.03, 711/103, 711/165, 711/154
• 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

1. A method for substantially preparing an erased block for use from a non-volatile memory of a non-volatile memory system, the non-volatile memory including a plurality of blocks, wherein the plurality of blocks includes the erased block, the method comprising:

obtaining the erased block;

obtaining an indicator that characterizes a number of times each block in the plurality of blocks has been erased;

storing the indicator that characterizes a number of times each block in the plurality of blocks has been erased in the erased block as an indication of a number of times the erased block has been erased;

determining when an indicator of a number of times the erased block has been erased is available, wherein obtaining the indicator that characterizes a number of times each block in the plurality of blocks has been erased includes obtaining the indicator that characterizes the number of times each block in the plurality of blocks has been erased when it is determined that the indicator of the number of times the erased block has been erased is not available, and storing the indicator that characterizes the number of times each block in the plurality of blocks has been erased includes storing the indicator that characterizes the number of times each block in the plurality of blocks has been erased when it is determined that the indicator of the number of times the erased block has been erased is not available; and

storing the indicator of the number of times the erased block has been erased in the erased block when it is determined that the indicator of the number of times the erased block has been erased is available, wherein when the indicator of the number of times the erased block has been erased is stared in the erased block, the indicator that characterizes the number of times each block in the plurality of blocks has been erased is not stored in the erased block.

2. The method of claim 1 wherein the indicator that characterizes the number of times each block in the plurality of blocks has been erased is an average erase count which substantially indicates an average number of times each block in the plurality of blocks has been erased.

3. The method of claim 1 wherein storing the indicator of the number of times the erased block has been erased includes storing the indicator of the number of times the erased block has been erased in an overhead area of the erased block.

4. The method of claim 1 wherein storing the that characterizes the number of times each block in the plurality of blocks has been erased in the erased block includes storing the indicator that characterizes the number of times each block in the plurality of blocks has been erased in an overhead area of the erased block.