Zone boundary adjustment for defects in non-volatile memories
A non-volatile memory is divided into logical zones by the card controller in order reduce the size of the data structures it uses for address translation. Zone boundaries are adjusted to accommodate defects allowed by memory test to improve card yields and to adjust boundaries in the field to extend the usable lifetime of the card. Firmware scans for the presence of defective blocks on the card. Once the locations of these blocks are known, the firmware calculates the zone boundaries in such a way that good blocks are equally distributed among the zones. Since the number of good blocks meets the card test criteria by the memory test criteria, defects will reduce card yield fallout. The controller can perform dynamic boundary adjustments. When defects occur, the controller can perform the analysis again and, if needed, redistributes the zone boundaries, moving any user data.
1. In a non-volatile memory system comprising a memory having a plurality of physical blocks of non-volatile storage elements, wherein the storage elements within individual ones of the blocks are simultaneously erasable, and a memory controller circuit that controls programming of data into addressed blocks, reading data from addressed blocks and erasing data from one or more addressed blocks at a time, wherein for address translation the controller organizes the non-volatile storage elements into logical subdivisions of the physical memory each comprised of one or more blocks, a method comprising:
providing test criteria, including a minimum number of non-defective blocks for each of said logical subdivisions;
testing said memory blocks to determine defective ones of the memory blocks; and
assigning a correspondence of blocks to zones based on the results of said testing so that said test criteria are met.
2. The method of claim 1 , wherein said testing is performed in response to a signal external to said controller.
3. The method of claim 1 , further comprising assembling said correspondence into a table.
4. The method of claim 3 , wherein the controller has a volatile memory in which said first correspondence is maintained.
5. The method of claim 3 , wherein said table is stored in non-volatile storage elements of the memory.
6. The method of claim 5 , wherein said table is stored in non-volatile storage elements of the memory.
7. The method of claim 6 , wherein the table is stored in a reserved area of the memory.
8. The method of claim 1 , wherein said memory system further comprises error correction code (ECC) logic and said testing is performed in response to a error correction code result.
9. The method of claim 1 , further comprising adjusting said correspondence in response to a block formerly determined to be non-defective subsequently becoming defective.
10. The method of claim 9 , wherein said adjusting is. performed in response to a program verification result.
11. The method of claim 9 , wherein said adjusting is performed in response to an erase verification result.
12. The method of claim 1 , wherein said assigning comprises distributing blocks to zones based on minimizing the variation in the number of non-defective blocks in said zones.