Method and managing bad memory blocks in a nonvolatile memory device, and nonvolatile-memory device implementing the management method
A method for managing bad memory blocks of a nonvolatile-memory device, in which the available memory blocks are divided into a first set, formed by addressable memory blocks that are to be used by a user, and a second set, formed by spare memory blocks that are to replace bad addressable memory blocks, and in which the bad addressable memory blocks are re-mapped into corresponding spare memory blocks. The re-mapping of the bad addressable memory blocks envisages: seeking bad spare memory blocks; storing the logic address of each bad spare memory block in a re-directing vector in a position corresponding to that of the bad spare memory block in the respective set; seeking bad addressable memory blocks; and storing the logic address of each bad addressable memory block in a free position in the re-directing vector.
1 . A method for managing bad memory blocks in a nonvolatile-memory device, said nonvolatile-memory device comprising a plurality of available memory blocks, each of which associated to a respective logic address, said management method comprising the steps of:
dividing the available memory blocks into a first set and a second set, the first set being formed by addressable memory blocks that are to be used by a user, and the second set being formed by spare memory blocks reserved to the replacement of bad addressable memory blocks; each memory block assuming, in the respective set, a respective position; and
re-mapping the bad addressable memory blocks in corresponding spare memory blocks;
said step of re-mapping comprising the step of:
constructing a data base containing, for each bad addressable memory block, information indicating the logic address of the corresponding spare memory block;
said step of creating a data base comprises the steps of:
seeking bad spare memory blocks;
storing the logic address of each bad spare memory block in a re-directing vector in a position corresponding to that of the bad spare memory block in the respective set;
seeking bad addressable memory blocks; and
storing the logic address of each bad addressable memory block in a free position in the re-directing vector.
2 . The management method according to claim 1 , further comprising the steps of:
detecting a request for access to an addressable memory block;
verifying whether the address of said addressable memory block is contained in the re-directing vector;
if the address of the addressable memory block is not contained in the re-directing vector, enabling access to said addressable memory block;
if the address of the addressable memory block is contained in the re-directing vector, reading the position of its address in the re-directing vector, and re-directing access to the spare memory block, which has, in the respective set, a position corresponding to that of the address of the addressable memory block in the re-directing vector.
3 . The management method according to claim 1 , wherein the step of storing the logic address of a bad spare memory block in the re-directing vector in a position corresponding to that of the bad spare memory block in the respective set comprises the steps of:
verifying whether in the re-directing vector said position is already occupied by the address of a bad addressable memory block;
if said position is free, storing the logic address of the bad spare memory block in said free position;
if said position is occupied by the address of a bad addressable memory block, shifting said address into a free position in the re-directing vector, and storing the logic address of the bad spare memory block in the position thus freed.
4 . The management method according claim 1 , for a nonvolatile-memory device wherein each memory block is divided into a plurality of pages, each page being formed by a plurality of bytes, wherein the step of seeking bad memory blocks comprises the step of:
verifying whether a specific byte of a specific page of a bad memory block assumes a value different from a given reference value.
5 . The management method according to claim 1 , in which the logic addresses of the bad addressable memory blocks are stored in the re-directing vector starting from the lowest positions.
6 . A nonvolatile-memory device comprising a plurality of memory blocks, and means for managing bad memory blocks, wherein said management means are configured in such a way as to implement a management method comprising the steps of:
dividing the available memory blocks into a first set and a second set, the first set being formed by addressable memory blocks that are to be used by a user, and the second set being formed by spare memory blocks reserved to the replacement of bad addressable memory blocks; each memory block assuming, in the respective set, a respective position; and
re-mapping the bad addressable memory blocks in corresponding spare memory blocks;
said step of re-mapping comprising the step of:
constructing a data base containing, for each bad addressable memory block, information indicating the logic address of the corresponding spare memory block;
said step of creating a data base comprises the steps of:
seeking bad spare memory blocks;
storing the logic address of each bad spare memory block in a re-directing vector in a position corresponding to that of the bad spare memory block in the respective set;
seeking bad addressable memory blocks; and
storing the logic address of each bad addressable memory block in a free position in the re-directing vector.