JP4952740B2 - MEMORY CONTROLLER, FLASH MEMORY SYSTEM HAVING MEMORY CONTROLLER, AND FLASH MEMORY CONTROL METHOD - Google Patents

Description

  The present invention relates to a memory controller, a flash memory system including the memory controller, and a flash memory control method.

  For example, as disclosed in Patent Document 1, in a memory system using a flash memory, wear leveling control is performed so that rewriting does not concentrate on a specific physical block. There are roughly two types of wear leveling control.

  One is wear leveling control (dynamic wear leveling) that controls the physical blocks in which data that is not rewritten is stored and the number of rewrites of other physical blocks is averaged. (Dynamic-wear-leveling) control method or control method called passive wear-leveling control method, hereinafter referred to as dynamic wear leveling). The other is wear leveling control (static wear leveling (Static Wear Leveling)) that controls the number of rewrites of all physical blocks, including physical blocks that store data that will not be rewritten. -wear-leveling) control method or active wear-leveling control method (hereinafter referred to as static wear leveling).

  Here, when there are few physical blocks in which data that is not rewritten is stored, the dynamic wear leveling control method is suitable. However, when there are many physical blocks in which data that is not rewritten is stored, the static wear leveling control method is suitable. Therefore, Patent Document 1 discloses dynamic wear according to the frequency of rewriting data stored in the memory system (that is, depending on whether there are many or few physical blocks storing data that is not rewritten). It is described that the wear leveling control is performed among the leveling control method, the static wear leveling control method, or the wear leveling control method combining these.

JP 2007-133683 A

  However, it is not always easy to select an appropriate wear leveling control method according to the frequency of rewriting data stored in the memory system.

  In Patent Document 1 described above, the user selects a wear leveling control method and sets conditions. At that time, the user needs to select an appropriate wear leveling control method and set the condition. These are burdens on the user. And if the wear leveling control method is not selected properly, for example, it is unnecessary if the static wear leveling control method is selected when there are few physical blocks that store data that will not be rewritten. Data transfer is often performed.

  Therefore, the present invention provides a memory controller, a flash, and the like that perform wear leveling control including a physical block only when there is a physical block in which data that is hardly rewritten (data with low rewrite frequency) is stored. An object of the present invention is to provide a memory system and a flash memory control method.

A memory controller according to a first aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Data writing means for writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
Count means for updating a count value every time the logical block is newly assigned to the physical block;
Count information writing means for writing the count information determined based on the count value to the physical block to which the logical block is newly assigned,
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Whether the data stored in the physical block is transferred to the free block detected by the free block search means for the physical block to which the predetermined logical block is assigned is counted as Determination means for determining based on the count information written in the physical block;
Information holding means for holding information for specifying the predetermined logical block;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means With.

A memory controller according to a second aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Data writing means for writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
Count means for updating a count value every time the logical block is newly assigned to the physical block;
Count information writing means for writing the count information determined based on the count value to the physical block to which the logical block is newly assigned,
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Processing target block specifying means for specifying a processing target block that is the physical block to which the predetermined logical block is allocated;
Information holding means for holding information for specifying the predetermined logical block;
Whether to transfer the data stored in the processing target block to the free block detected by the free block searching means is based on the count value and the count information written in the processing target block. A judging means for judging;
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means Means.

A memory controller according to a third aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When a new table storage block is assigned by the table storage block management means, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. Count information writing means for updating and writing the latest count value that is the updated count value to the physical block newly assigned as the table storage block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Whether to transfer the data stored in the physical block to the free block detected by the free block search means for the physical block to which the predetermined logical block is assigned is determined as the physical block. Determining means for determining based on the version number information written in
Information holding means for holding information for specifying the predetermined logical block;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means With.

A memory controller according to a fourth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When a new table storage block is assigned by the table storage block management means, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. Count information writing means for updating and writing the latest count value that is the updated count value to the physical block newly assigned as the table storage block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Processing target block specifying means for specifying a processing target block that is the physical block to which the predetermined logical block is allocated;
Information holding means for holding information for specifying the predetermined logical block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means Means.

A memory controller according to a fifth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information Management information storage means to be stored in the block;
Management information block management means for newly allocating another physical block as the management information block when there is no free space for storing the management information in the management information block;
When a new management information block is allocated by the management information block management means, the count value immediately before the count value that matches the count value stored in the management information block in which a free area has disappeared is obtained. Count information writing means for updating and writing the latest count value, which is the updated count value, to the physical block newly assigned as the management information block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Whether to transfer the data stored in the physical block to the free block detected by the free block search means for the physical block to which the predetermined logical block is assigned is determined as the physical block. Determining means for determining based on the version number information written in
Information holding means for holding information for specifying the predetermined logical block;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means With.

A memory controller according to a sixth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information Management information storage means to be stored in the block;
Management information block management means for newly allocating another physical block as the management information block when there is no free space for storing the management information in the management information block;
When a new management information block is allocated by the management information block management means, the count value immediately before the count value that matches the count value stored in the management information block in which a free area has disappeared is obtained. Count information writing means for updating and writing the latest count value, which is the updated count value, to the physical block newly assigned as the management information block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Processing target block specifying means for specifying a processing target block that is the physical block to which the predetermined logical block is allocated;
Information holding means for holding information for specifying the predetermined logical block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means Means.

A memory controller according to a seventh aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Count means for updating the count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version information management means for updating
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Whether to transfer the data stored in the physical block to the free block detected by the free block search means for the physical block to which the predetermined logical block is assigned is determined as the physical block. Determining means for determining based on the version number information written in
Information holding means for holding information for specifying the predetermined logical block;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means With.

A memory controller according to an eighth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Count means for updating the count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version information management means for updating
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Processing target block specifying means for specifying a processing target block that is the physical block to which the predetermined logical block is allocated;
Information holding means for holding information for specifying the predetermined logical block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means Means.

A memory controller according to a ninth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Means for searching for the physical block in the erased state in the flash memory, the free block searching means for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
Logical block allocation means for allocating the logical block to the physical block in the erased state detected by the free block search means;
Version number information management means for updating the version number information to be written in the physical block to which the logical block is assigned each time the search in the predetermined order in the empty block search means circulates a predetermined number of times,
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Whether to transfer the data stored in the physical block to the free block detected by the free block search means for the physical block to which the predetermined logical block is assigned is determined as the physical block. Determining means for determining based on the version number information written in
Information holding means for holding information for specifying the predetermined logical block;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means With.

A memory controller according to a tenth aspect of the present invention is a memory controller that controls access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Means for searching for the physical block in the erased state in the flash memory, the free block searching means for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
Logical block allocation means for allocating the logical block to the physical block in the erased state detected by the free block search means;
Version number information management means for updating the version number information to be written in the physical block to which the logical block is assigned each time the search in the predetermined order in the empty block search means circulates a predetermined number of times,
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Processing target block specifying means for specifying a processing target block that is the physical block to which the predetermined logical block is allocated;
Information holding means for holding information for specifying the predetermined logical block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means Means.

  In the memory controller according to the eleventh aspect of the present invention, in any one of the first to tenth aspects, information for specifying the predetermined logical block is set based on information given from a host system. The

  A flash memory system according to a twelfth aspect of the present invention includes a memory controller according to any one of the first to eleventh aspects, and a flash memory controlled by the memory controller.

A method according to a thirteenth aspect of the present invention is a flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system.
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A data writing step of writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
A count step of updating a count value every time the logical block is newly assigned to the physical block;
Count information writing step for writing count information determined based on the count value to the physical block to which a new logical block is allocated;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
A processing target block specifying step for specifying a processing target block that is the physical block to which the predetermined logical block is assigned;
Whether to transfer the data stored in the processing target block to the free block detected by the free block search step is determined based on the count value and the count information written in the processing target block. A judgment step to judge;
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step Steps.

A method according to a fourteenth aspect of the present invention is a flash memory control method for controlling access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A logical block allocation step for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
An address translation table management step for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation step;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management step And an address conversion table storing step for storing the address conversion table;
A table storage block management step for newly allocating another physical block as the table storage block when there is no more free space in the table storage block for storing the address conversion table;
When a new table storage block is assigned by the table storage block management step, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. A count information writing step of updating and writing the latest count value, which is the updated count value, into the physical block newly assigned as the table storage block;
A version number information determining step for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
A version number information writing step of writing the version number information determined in the version number information determination step into the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
A processing target block specifying step for specifying a processing target block that is the physical block to which the predetermined logical block is assigned;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step Steps.

A method according to a fifteenth aspect of the present invention is a flash memory control method for controlling access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A logical block allocation step for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
An address translation table management step for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation step;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management step And an address conversion table storing step for storing the address conversion table;
A table storage block management step for newly allocating another physical block as the table storage block when there is no more free space in the table storage block for storing the address conversion table;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information A management information storage step to be stored in the block;
A management information block management step for newly assigning another physical block as the management information block when there is no more free space in the management information block for storing the management information;
When a new management information block is allocated by the management information block management step, the count value immediately before that is the count value that matches the count value stored in the management information block that has no free space is updated. A count information writing step of writing the latest count value, which is the updated count value, into the physical block newly assigned as the management information block;
A version number information determining step for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
A version number information writing step of writing the version number information determined in the version number information determination step into the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
A processing target block specifying step for specifying a processing target block that is the physical block to which the predetermined logical block is assigned;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step Steps.

A method according to a sixteenth aspect of the present invention is a flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A count step of updating a count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version number information management step to update,
A version number information writing step for writing the version number information to the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
A processing target block specifying step for specifying a processing target block that is the physical block to which the predetermined logical block is assigned;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step Steps.

A method according to a seventeenth aspect of the present invention is a flash memory control method for controlling access to a flash memory to be erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A search for the physical block in the erased state in the flash memory, and a free block search step for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
A logical block allocation step of allocating the logical block to the physical block in the erased state detected in the empty block search step;
A version number information management step for updating version number information to be written in the physical block to which the logical block is allocated each time the search in the predetermined order in the empty block search step circulates a predetermined number of times,
A version number information writing step for writing the version number information to the physical block to which the logical block is newly assigned;
A processing target block specifying step for specifying a processing target block that is the physical block to which the predetermined logical block is assigned;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step Steps.

  In the method according to the eighteenth aspect of the present invention, in any of the thirteenth to seventeenth aspects, the predetermined logical block is set based on information given from a host system.

  According to the present invention, it is possible to appropriately set whether or not a physical block in which data corresponding to each logical block is stored is subject to wear leveling control in units of logical blocks. Therefore, if the data given by the host system includes data that you want to be subject to wear leveling control and data that you do not want to be subject to wear leveling control, only the data that you want to be subject to wear leveling control. It can be set as a target of wear leveling control.

1 is a block diagram showing a schematic configuration of a flash memory system according to an embodiment of the present invention. It is a figure which shows the correspondence of a logical block and a physical block. It is explanatory drawing of the process performed when a logical block is newly allocated with respect to the physical block. It is explanatory drawing of the wear leveling control performed when the physical block in which the data with low rewriting frequency is memorize | stored is detected. It is a flowchart which shows the flow of the process performed by one Embodiment of this invention. Table management information and address conversion tables and how to store them are shown. FIG. 7A shows a rewrite mark change rule. FIG. 7B is an explanatory diagram of processing performed when a logical block is newly assigned to a physical block. It is explanatory drawing of the data transfer process performed when the physical block in which the data with low rewriting frequency are memorize | stored is detected. It is a flowchart which shows the flow of the process performed by one Embodiment of this invention. FIG. 10A shows a flash memory in which a physical block storing a rewrite mark and a physical block storing a change count value are mixed. FIG. 10B shows the flow of processing relating to the first example in which the rewrite mark is updated. FIG. 11A shows a flash memory in which a physical block storing a rewrite mark and a physical block storing a switching count value are mixed. FIG. 11B shows the flow of processing relating to the second example in which the rewrite mark is updated. FIG. 12A shows the flow of processing relating to the third example in which the rewrite mark is updated. FIG. 12B shows the flow of processing relating to the fourth example in which the rewrite mark is updated.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram schematically showing a flash memory system 1 according to the first embodiment of the present invention.

  As shown in FIG. 1, the flash memory system 1 includes a flash memory 2 and a memory controller 3 that controls the flash memory 2.

  The flash memory system 1 is connected to the host system 4 via the external bus 13. The host system 4 is composed of a CPU (Central Processing Unit) for controlling the entire operation of the host system 4, a companion chip for transferring information to and from the flash memory system 1, and the like. The host system 4 may be various information processing apparatuses such as a personal computer and a digital still camera that process various types of information such as characters, sounds, and image information.

  As shown in FIG. 1, the memory controller 3 includes a microprocessor 6, a host interface block 7, a work area 8, a buffer 9, a flash memory interface block 10, an ECC (Error Correcting Code) block 11, and a ROM. (Read Only Memory) 12. The memory controller 3 is connected to the flash memory 2 via the internal bus 14. The memory controller 3 constituted by these functional blocks is integrated on one semiconductor chip. Hereinafter, each functional block will be described.

  The host interface block 7 exchanges data, address information, status information, external commands and the like with the host system 4. The external command is a command for the host system 4 to instruct the flash memory system 1 to execute processing. Data or the like supplied from the host system 4 to the flash memory system 1 is taken into the flash memory system 1 (for example, the buffer 9) using the host interface block 7 as an entrance. Data supplied from the flash memory system 1 to the host system 4 is supplied to the host system 4 through the host interface block 7 as an exit.

  The host interface block 7 includes a command register R1, a sector number register R2, and an LBA register R3. Information given from the host system 4 is written in the command register R1, the sector number register R2, and the LBA register R3. External commands such as a write command and a read command are written in the command register R1. The number of sectors in the access target area is written in the sector number register R2. LBA (Logical Block Address) (described later) of the access target area is written in the LBA register R3.

  The work area 8 is a work area for temporarily storing data necessary for controlling the flash memory 2, and is composed of a plurality of SRAM (Static Random Access Memory) cells. The work area 8 stores, for example, an address conversion table (described later) indicating the correspondence between logical blocks and physical blocks.

  The buffer 9 holds the data read from the flash memory 2 until the host system 4 can receive the data. The buffer 9 holds data to be written to the flash memory 2 until the flash memory 2 is in a writable state.

  The flash memory interface block 10 exchanges data, address information, status information, internal commands, and the like with the flash memory 2 via the internal bus 14. Here, the internal command is a command for the memory controller 3 to instruct the flash memory 2 to execute processing, and the flash memory 2 operates in accordance with the internal command given from the memory controller 3.

  The ECC block 11 generates an error correcting code (ECC) added to data to be written to the flash memory 2 and is included in the read data based on the error correcting code added to the read data. Detect and correct errors.

  The ROM 12 is a non-volatile storage element that stores a program that defines a processing procedure performed by the microprocessor 6. For example, a program that defines a processing procedure such as creation of an address conversion table is stored.

  The microprocessor 6 controls the overall operation of the memory controller 3 in accordance with a program stored in the ROM 12. For example, the microprocessor 6 causes the flash memory interface block 10 to execute processes based on a command set that defines various processes read from the ROM 12.

  The flash memory 2 is a NAND flash memory. The NAND flash memory includes a register and a memory cell array in which a plurality of memory cells are two-dimensionally arranged. The memory cell array includes a plurality of memory cell groups and word lines. Here, the memory cell group is a group in which a plurality of memory cells are connected in series. Each word line is for selecting a specific memory cell in the memory cell group. Data is written from the register to the selected memory cell or data is read from the selected memory cell to the register between the selected memory cell and the register via the word line.

  In the NAND flash memory, a data read operation and a data write operation are performed in units of pages, and a data erase operation is performed in units of blocks (physical blocks). A physical block is composed of a plurality of pages (physical pages). For example, one physical page includes a user area of a predetermined size (for example, 2048 bytes) and a redundant area of a predetermined size (for example, 64 bytes), and one physical block has a predetermined number (for example, 64). It consists of physical pages. The user area is an area for storing data provided from the host system 4, and is configured by a predetermined number (for example, four) of physical sector areas (for example, a storage area of 512 bytes). The redundant area is an area for storing additional data such as error correcting code (ECC), logical address information, block status (flag), and count information (described later).

  The logical address information is information for determining the correspondence between physical blocks and logical blocks. Therefore, for a physical block having no corresponding logical block, such as a physical block from which stored data has been erased, no logical address information is stored in the redundant area of the physical block. In the following description, the “redundant area of the physical block” refers to a storage area configured by a redundant area (for example, a redundant area of the first physical page) included in one or more physical pages in the physical block.

  The block status (flag) is a flag indicating pass / fail of the physical block. For the initial defective physical block, a block status (flag) indicating a defective block (physical block in which data cannot be normally written) is written by the manufacturer. Some manufacturers also write a block status (flag) indicating the initial defective physical block in the user area.

  In the writing process of the present embodiment, the host system 4 writes a command code indicating a write command in the command register R1, writes the number of sectors of data to be written in the sector number register R2, and stores in the LBA register R3 The LBA corresponding to the top data to start writing is written. Based on the information written in the sector number register R2 and the LBA register R3, a logical access area that is an access target area is determined and given to the physical block corresponding to the logical block including the logical access area from the host system 4. Data is written.

  When the logical access area determined based on the information written in the sector number register R2 and the LBA register R3 extends over a plurality of logical blocks, the data write destination is a plurality of physical blocks. Therefore, when the logical access area extends over a plurality of logical blocks, the area is divided for each logical block to which the logical access area belongs, and data write processing is performed. For example, when the logical access area extends over two logical blocks (the first logical block and the second logical block), the write processing for the physical block corresponding to the first logical block and the second logical block Write processing is performed on the physical block corresponding to the block. Data instructed to be written to the logical access area belonging to the first logical block is written to the physical corresponding to the first logical block. Data instructed to be written to the logical access area belonging to the second logical block is written into the physical block corresponding to the second logical block.

  The address space on the host system 4 side is managed by an LBA (Logical Block Address) which is a serial number assigned to an area (hereinafter referred to as a logical sector area) divided in units of sectors (512 bytes). Also, a logical block composed of a plurality of logical sector areas is formed, and one or a plurality of physical blocks are assigned to the logical block.

  The correspondence between logical blocks and physical blocks is often managed on a zone basis. Specifically, one logical zone is composed of a plurality of logical blocks, one physical zone is composed of a plurality of physical blocks, and the logical zone is managed in association with the physical zone. Many.

  However, in this case, when access is concentrated in a specific logical zone, the number of rewrites of physical blocks included in the physical zone corresponding to the logical zone where access is concentrated is greater than the number of rewrites of physical blocks included in other physical zones. Is also undesirable.

  As a method for solving this problem, there is a method in which logical blocks having consecutive logical block numbers (LBNs), which are serial numbers assigned to the logical blocks, are allocated to each logical zone.

  However, when access concentrates on a specific logical block (when the access concentration range does not extend over a plurality of logical blocks), the physical included in the physical zone corresponding to the logical zone including the logical block The number of block rewrites is larger than the number of rewrites of physical blocks included in other physical zones. In such a case, it is preferable not to limit the physical blocks that can be associated with the logical blocks included in each logical zone. In other words, it is preferable that a logical block included in each logical zone can correspond to any physical block without forming a physical zone.

  The correspondence between logical blocks and physical blocks is usually managed by an address conversion table that is a table describing the correspondence between logical blocks and physical blocks. When the correspondence between the logical block and the physical block changes, the address conversion table is updated in the work area (SRAM) 8. The address conversion table is generally created based on logical address information stored in the redundant area of each physical block at the time of startup or access, but is stored in the flash memory 2 and read from the flash memory 2. You can also. As a result, the address conversion table can be obtained in a shorter time than reading the logical address information from the redundant area of each physical block and creating the address conversion table. In particular, the address translation table is stored in the flash memory 2 when the logical blocks included in each logical zone can be associated with any physical block without configuring the physical zone as described above. It is better to keep it.

  When the address conversion table is stored in the flash memory 2, it is preferable that the latest address conversion table is always stored in the flash memory 2 in order to cope with a sudden power interruption. That is, each time the correspondence between the logical block and the physical block changes (that is, every time the address conversion table is updated on the work area 8), the latest address conversion table is stored in the flash memory 2. Is preferred. Considering the time taken to store the address conversion table in the flash memory 2, it is preferable to store (manage) the address conversion table in units of logical zones and reduce the number of logical blocks included in each logical zone. .

  Therefore, in this embodiment, as shown in FIG. 2, a logical zone is formed, but a physical zone is not formed. Regardless of which logical zone, the entire range of physical blocks is assigned to each logical zone. Accordingly, any logical block may be assigned to any physical block.

  With reference to FIG. 2, the correspondence between the logical block and the physical block will be described.

  In this embodiment, as shown in FIG. 2, 2048000 logical sector areas composed of LBA # 0 to # 20479999 are allocated to a storage area on the flash memory 2 side composed of 8192 physical blocks.

  In FIG. 2, a group of 256 logical sector areas having consecutive addresses (LBA) is defined as a logical block, and the above-described LBN is attached to this logical block. For example, the 256 logical sector areas of LBA # 0- # 255 belong to the logical block of LBN # 0, and the 256 logical sector areas of LBA # 256- # 511 belong to the logical block of LBN # 1. Yes. As described above, the 2048,000 logical sector areas of LBA # 0 to # 20479999 belong to one of 8000 logical blocks of LBN # 0 to # 7999.

  In addition, a plurality of logical blocks are collected as a logical zone, and the above-described LZN is added to the logical zone. In FIG. 2, each logical block is sequentially allocated to the eight logical zones LZN # 0 to # 7 so that logical blocks with consecutive LBNs belong to different logical zones. For example, the logical block of LBN # 0 is in the logical zone of LZN # 0, the logical block of LBN # 1 is in the logical zone of LZN # 1, the logical block of LBN # 2 is in the logical zone of LZN # 2, The logical blocks are distributed to the logical zone of LZN # 7. Similarly, the logical block of LBN # 8 is allocated to the logical zone of LZN # 0, the logical block of LBN # 9 is allocated to the logical zone of LZN # 1, and the logical block of LBN # 10 is allocated to the logical zone of LZN # 2. It will be. By performing such distribution, it is possible to reduce the probability that logical blocks corresponding to logical access areas with high rewrite frequency are concentrated in a specific logical zone. Therefore, it is possible to suppress the change frequency of the table storage block corresponding to a specific logical zone from becoming significantly higher than the change frequency of the table storage block corresponding to another logical zone.

  The flash memory 2 is composed of, for example, 8192 physical blocks. A unique physical block address (PBA) is assigned to 8192 physical blocks. The flash memory 2 may have a congenital defective physical block that is defective from the time of shipment. Further, the flash memory 2 may include a physical block (acquired defective block) that deteriorates after the start of use even if it is a good physical block at the time of shipment.

  In the NAND flash memory, a data read operation and a data write operation are performed in units of pages, and a data erase operation is performed in units of physical blocks. In the data erasure operation, the data stored in the physical block corresponding to the logical block to which the logical access area belongs (hereinafter referred to as “write destination logical block”) or the latest data corresponding to the data is written in another physical block. This is performed when all the data stored in the physical block is replaced with data written in another physical block. That is, when the data stored in the physical block corresponding to the write destination logical block is all replaced with the data written in another physical block, the data stored in the physical block is erased, The correspondence relationship between the logical block and the physical block described in the address conversion table (the table describing the correspondence relationship between the logical block and the physical block) is updated. When searching for a free physical block to which a write destination logical block is newly assigned (a physical block to which no logical block is assigned) is searched, for example, a free space is sequentially provided from the first physical block to the last physical block in the flash memory 2. The physical block is searched. Then, a write destination logical block is allocated to the detected free physical block.

  As described above, when data stored in a physical block is rewritten, a logical block corresponding to the physical block is newly added to a physical block (empty physical block) different from the physical block. Will be assigned. Further, even when there is no physical block corresponding to the write destination logical block, a logical block is newly allocated to an empty physical block.

  In the present embodiment, the memory controller 3 is provided with a counter function that counts up the count value each time a new logical block is allocated to a physical block. Specifically, for example, the microprocessor 6 plays the role of a counter and counts up the count value every time a new logical block is assigned to a physical block. The count value is stored in a storage area in the memory controller 3, for example, a work area 6 (volatile memory such as SRAM), and the count value stored in the work area 6 is counted up. The count value stored in the work area 6 is copied (written) to the flash memory 2 in a timely manner (for example, every time the count value is updated a predetermined number of times). When the memory controller 3 is powered off, the count value stored in the work area 6 is erased. However, when the memory controller 3 is powered on, the count value stored in the flash memory 2 is It is read to the work area 6 and the read count value is counted up thereafter. Note that the count value is not limited to counting up, and may be updated according to other rules such as counting down. Further, in this embodiment, the timing at which the count value is updated is every time a new logical block is allocated to the physical block. However, the timing is not limited to this, but other timing, for example, the storage data of the physical block is updated. The timing at which erasure is performed may be used. Further, the memory controller 3 may have a storage area composed of a nonvolatile RAM such as a FeRAM (Ferroelectric Random Access Memory) or MRAM (Magnetic Random Access Memory), and the count value may be held in this storage area. When the count value is held in such a nonvolatile RAM, the count value can be updated on the nonvolatile RAM, and it is not necessary to copy the count value to the flash memory 2.

  When a new logical block is allocated to a physical block, the logical address information indicating the newly allocated logical block and the count before counting up are added to the redundant area of the physical block to which the new logical block is allocated. Count information based on a value (or a count value after counting up) may be written. Specifically, for example, as shown in FIG. 3, LBN indicating the assigned logical block is written as the logical address information in the redundant area 105 of the physical block to which the new logical block is assigned, and the count information is provided as the count information. The upper 3 bytes of the 4-byte count value before counting up are written.

  More specifically, according to the example shown in FIG. 3, as shown in (3A), when the count value (in hexadecimal notation) is “00 00 3F FAh”, it is detected as an empty physical block. When the logical block of LBN # 40 is newly assigned to the physical block of PBA # 7, the LBN “# 40” of the logical block newly assigned to the redundant area 105 of the physical block of PBA # 7, Count information “00 00 3Fh”, which is the upper 3 bytes of the count value before counting up, is written. Then, the count value (in hexadecimal notation) is counted up from “00 00 3F FAh” to “00 00 3F FBh”.

  Next, for example, as shown in (3B), when a logical block of LBN # 41 is newly assigned to a physical block of PBA # 12 detected as an empty physical block, the physical block of that PBA # 12 In the redundant area 105, LBN “# 41” of the newly allocated logical block and count information “00 00 3Fh” which is the upper 3 bytes of the count value before counting up are written. Then, the count value is counted up from “00 00 3F FBh” to “00 00 3F FCh”.

  Thereafter, similarly, every time a new logical block is assigned to a physical block, the LBN of the assigned logical block and the LBN of the assigned logical block are added to the redundant area 105 of the newly assigned physical block. The count information which is the upper 3 bytes of the count value is written, and the count value is counted up. For example, as shown in (3C), when a logical block of LBN # 42 is assigned to a physical block of PBA # 18, LBN “# 42” and count information “ “00 00 3Fh” is written, and the count value is counted up from “00 00 3F FCh” to “00 00 3F FDh”. Next, as shown in (3D), when the logical block of LBN # 43 is allocated to the physical block of PBA # 22, LBN “# 43” and the count are added to the redundant area 105 of the physical block of PBA # 22. Information “00 00 3Fh” is written, and the count value is counted up from “00 00 3F FDh” to “00 00 3F FEh”. Next, as shown in (3E), when the logical block of LBN # 44 is allocated to the physical block of PBA # 27, the LBN “# 44” and the count are added to the redundant area 105 of the physical block of PBA # 27. Information “00 00 3Fh” is written, and the count value is counted up from “00 00 3F FEh” to “00 00 3F FFh”. Next, as shown in (3F), when the logical block of LBN # 45 is allocated to the physical block of the physical block of PBA # 31, the LBN “# 45” is assigned to the redundant area 105 of the physical block of PBA # 31. "And count information" 00 00 3Fh "are written, and the count value is counted up from" 00 00 3F FFh "to" 00 00 40 00h ".

  A free block search for searching for a physical block to which a new logical block is newly assigned is performed for all physical blocks in the physical zone or used as a storage area of the host system. In the search for the physical block in the physical zone, the search for the empty block is sequentially performed from the first physical block in the physical zone to the last physical block. In a search for all physical blocks used as a storage area of the host system, empty blocks are sequentially searched from the first physical block to the last physical block for all the physical blocks. In this way, for the physical blocks included in the range to be searched, the search for empty blocks in the order from the first physical block to the last physical block is repeatedly performed, so that data that is hardly rewritten (rewrite frequency is If there is no physical block in which (low data) is stored, the number of rewrites of the physical block included in the search target range is expected to be substantially equal.

  According to the above description, in the process of rewriting (or writing) data, for example, when 8192 logical blocks are newly assigned to a physical block, the count value is 0 (hexadecimal number display: From 00 00 00 00h) to 8192 (hexadecimal display: 00 00 20 00h). When a new logical block is assigned to each physical block, the upper 3 bytes of the count value are written as count information in the redundant area 105 of each physical block. Therefore, any value from “00 00 00h” to “00 00 1Fh” is written as count information in the redundant area 105 of each physical block.

  After that, when 8192 logical blocks are newly allocated, the count value is counted up from 8192 (hexadecimal display: 00 00 20 00h) to 16384 (hexadecimal display: 00 00 40 00h). . During this period, any value from “00 00 20h” to “00 00 3Fh” is written as count information in the redundant area 105 of the physical block to which a new logical block is allocated.

  Here, for a physical block in which a value equal to or less than “00 00 1Fh” is written as count information, the count value is from 8192 (hexadecimal display: 00 00 20 00h) to 16384 (hexadecimal display: 00 00 40 00h). It can be seen that no new logical block is allocated during the period counted up to. This is because any value from “00 00 20” to “00 00 3F” is written as count information in the redundant area 105 of the physical block to which a new logical block is allocated during that period. This is because the count information having a value of “00 00 1Fh” or less is never written. Also, assuming that the total number of physical blocks is 1024 (in the example of FIG. 2, it is 8192, but here the total number of physical blocks is 1024 in order to make the following description easy to understand) There are physical blocks to which a new logical block has been allocated at least 8 times (8192 ÷ 1024) during this period.

  In this embodiment, for example, when the count value is counted up to 16384 (hexadecimal notation: 00 00 40 00h), the physical block storing data with low rewrite frequency is “00 00 1Fh” or less. Is searched for (for example, such physical blocks are sequentially searched from the first physical block to the last physical block). When such a physical block is detected, the data stored in the physical block is transferred (copied) to another physical block. Specifically, a physical block that is a transfer destination of data stored in the detected physical block (hereinafter referred to as “transfer source physical block”) (hereinafter referred to as “transfer destination physical block”) An empty block search is performed to search for. A logical block assigned to the transfer source physical block is newly assigned to the free block (transfer destination physical block) detected by this search, and the transfer source physical block is transferred to the transfer destination physical block. The data stored in is transferred (copied). Then, in the redundant area 105 of the physical block of the transfer destination, the LBN of the logical block newly allocated (LBN of the logical block allocated to the physical block of the transfer source) and the upper 3 of the count value before counting up Count information that is a byte is written. Thereafter, the data stored in the transfer source physical block and the additional data such as LBN and count information stored in the redundant area 105 of the physical block are erased. That is, the data stored in the user area of the transfer source physical block and the additional data stored in the redundant area are erased collectively. Further, since a logical block is newly assigned to the physical block, the count value is counted up. Hereinafter, a specific description will be given with reference to FIG.

  When the count value is counted up to 16384 (hexadecimal notation: 00 00 40 00h), a search is made for a physical block in which count information representing a value equal to or less than “00 00 1Fh” is stored. By this search, first, a physical block of PBA # 6 storing “00 00 1Ah” is detected. In this case, the data stored in the physical block of the PBA # 6 is copied to the physical block of the PBA # 34 detected as an empty physical block, and is also stored in the redundant area 105 of the physical block of the PBA # 34. The LBN “# 6” of the logical block allocated to the physical block of PBA # 6 and the count information “00 00 40h” that is the upper 3 bytes of the count value before counting up are written (see (4D)). ). After that, the data stored in the physical block of PBA # 6 and the additional data such as LBN “# 6” and count information “00 00 1Ah” stored in the redundant area 105 of the physical block of PBA # 6 Is deleted (see (4A)). Further, the count value is counted up from “00 00 40 00h” to “00 00 40 01h”.

  Next, the physical block of PBA # 15 storing “00 00 10h” is detected. In this case, the data stored in the physical block of the PBA # 15 is copied to the physical block of the PBA # 35 detected as an empty physical block, and the data is stored in the redundant area 105 of the physical block of the PBA # 35. The LBN “# 15” of the logical block assigned to the physical block of PBA # 15 and the count information “00 00 40h” that is the upper 3 bytes of the count value before counting up are written (see (4E)). ). After that, the data stored in the physical block of PBA # 15 and the additional data such as LBN “# 15” and count information “00 00 10h” stored in the redundant area 105 of the physical block of PBA # 15 Is deleted (see (4B)). The count value is counted up from “00 00 40 01h” to “00 00 40 02h”.

  Next, the physical block of PBA # 16 storing “00 00 0Fh” is detected. In this case, the data stored in the physical block of the PBA # 16 is copied to the physical block of the PBA # 36 detected as an empty physical block, and the data is stored in the redundant area 105 of the physical block of the PBA # 36. The LBN “# 16” of the logical block allocated to the physical block of PBA # 16 and the count information “00 00 40h” which is the upper 3 bytes of the count value before counting up are written (see (4F)). ). After that, the data stored in the physical block of PBA # 16 and additional data such as LBN “# 16” and count information “00 00 0Fh” stored in the redundant area 105 of the physical block of PBA # 16 Is deleted (see (4C)). Also, the count value is counted up from “00 00 40 02h” to “00 00 40 03h”.

  As described above, a physical block to which a new logical block is not allocated in a period from a count value of 8192 (hexadecimal display: 00 00 20 00h) to 16384 (hexadecimal display: 00 00 40 00h), that is, “00 00 A physical block in which a value of 1 Fh ″ or less is written as count information is regarded as a physical block with a low writing frequency, and wear leveling control including the physical block is performed. In other words, the count information (the count indicating a value less than “00 00 1Fh”) whose difference from “00 00 40” which is the upper 3 bytes (that is, the portion corresponding to the count information) in the current count value is a predetermined value or more. The physical block in which (information) is stored is regarded as a physical block with a low writing frequency. Note that the search value of the physical block with low write frequency and the data transfer process of copying the data stored in the physical block detected by this search process to another physical block do not necessarily have a count value of 16384 (hexadecimal number). It is not necessary to start immediately after reaching 00 00 40 00h), and idle time after the count value reaches 16384 (hexadecimal display: 00 00 40 00h) (for example, a period when there is no access from the host system 4) ). Further, when there is an access from the host system 4 during execution of these processes, the process may be temporarily stopped, and then the process may be resumed when the idle time occurs again.

  Thereafter, when the count value is further counted up from 16384 (hexadecimal display: 00 00 40 00h) to 24576 (hexadecimal display: 00 00 60 00h), a value equal to or less than “00 00 3Fh” is written as count information. A search is made for the physical block being stored. When such a physical block is detected, the data stored in the physical block is copied (transferred) to another physical block.

  As described above, the search for physical blocks that are not frequently rewritten is performed by multiplying the total number of physical blocks (for example, 1024) by a predetermined number (for example, 8) to obtain a new number (for example, 8192). It is preferably executed every time a logical block is assigned. That is, when the total number of physical blocks is n (n is an integer equal to or greater than 1) and the predetermined number k (k is an integer equal to or greater than 1), rewrite is frequently performed every time the count value increases by n × k. A search for missing physical blocks is performed. In this search, a search is made for a physical block to which a new physical block has not been assigned in a period in which the count value increases by n × k, and data with a low rewrite frequency is stored in the physical block detected by this search. Considered a physical block. Then, the data stored in the physical block is transferred (copied) to another physical block.

  A physical block that is regarded as a physical block in which data with low rewrite frequency is stored is erased after the data stored in the physical block is transferred (copied) to another physical block, It is considered as an empty physical block. There is a possibility that the physical block that has been made empty has a small number of rewrites up to that point. Conversely, the physical block that is the data copy destination may have a large number of rewrites up to that point, but the data with a low rewrite frequency may be copied, which may reduce the number of subsequent rewrites. Get higher. Based on such a principle, it can be expected that the number of rewrites of a plurality of physical blocks in the flash memory 2 is equalized.

  Note that the total number of physical blocks in the flash memory can be obtained based on ID information (information on the configuration of the flash memory 2) written in the flash memory 2. Specifically, for example, the ID information includes information indicating the storage capacity of the entire flash memory 2 and information indicating a block size (storage capacity of one physical block). The total number of physical blocks can be calculated from the storage capacity and block size of the entire memory 2. The count information may be all or a part of the count value, but the physical block that has not been rewritten for a predetermined period (the period until the count value increases by a predetermined value). The information must be distinguishable. When some bits of the count value are used as count information within this discriminable range, the count information bits take into account the storage capacity of the redundant area and the capacity of information other than the count information written to the redundant area. The number may be determined.

  Hereinafter, an outline of the flow of processing performed in the present embodiment will be described with reference to FIG.

  When performing wear leveling control according to the present embodiment, first, initial setting is performed (step 101). Specifically, for example, the memory controller 3 reads the ID information from the flash memory 2, and calculates the total number n of physical blocks based on the storage capacity and block size of the entire flash memory 2 ascertained from the ID information. To do. Further, it is determined that the search process and the data transfer process are executed every time the count value increases by n × k based on the calculated n and the predetermined number k. In addition, the count value of the counter is set to zero. The predetermined number k may be determined in advance, or may be determined based on the total number n of physical blocks. Further, the upper bytes of the count value to be used as the count information may be determined in advance or may be determined based on the total number n of physical blocks. Here, the upper 3 bytes of the count value are used as count information.

  After the initial setting, when the memory controller 3 receives a write command from the host system 4, it is necessary to newly set a physical block corresponding to the logical block to which the logical access area specified by the write command belongs. Is determined (step 102). If it is necessary (YES in step 102), the memory controller 3 searches for a free block and assigns a logical block to which the logical access area designated by the write command belongs to the detected free block (step). 103). Specifically, the LBN of the logical block to which the logical access area specified by the write command belongs to the redundant area 105 of the detected free block (physical block), and the count information that is the upper 3 bytes of the count value of the counter, Is written, and then the count value of the counter is counted up.

  It is determined whether or not the count value of the counter counted up in step 103 is a multiple of (n × k) (step 104). The multiple of (n × k) is 8192, 16384, 24576,... In the above example (n = 1024, k = 8).

  If it is determined that the count value after the count-up is a multiple of (n × k) (YES in step 104), a search process of a physical block storing data with low rewrite frequency is performed, and rewrite is performed. When a physical block in which infrequent data is stored is detected, data transfer processing for copying the data stored in the detected physical block to another physical block is performed (step 105). Specifically, when the count value of the counter reaches a multiple of (n × k), a physical block to which a logical block is not newly allocated is searched within a period in which the count value has increased (n × k). The That is, when the count value of the counter reaches a multiple of (n × k), physical information in which count information corresponding to a value smaller than the value obtained by subtracting the value of (n × k) from the count value is written. A block search is performed. When a physical block corresponding to this is detected, the data stored in the detected physical block is transferred to another physical block, and then the stored data in the detected physical block is erased. .

  In step 105, data transfer processing is not performed unless a physical block storing data with low rewrite frequency is detected, but data transfer is performed when a physical block storing data with low rewrite frequency is detected. Processing is performed. That is, only when there is a physical block storing data with low rewrite frequency, data transfer processing for copying data with low rewrite frequency stored in the physical block to another physical block is performed.

  The above is the description of the present embodiment.

  According to this embodiment, the memory controller 3 is provided with a counter function that counts up the count value each time a new logical block is assigned to a physical block. The count information based on the count value managed by the counter function is written in the redundant area 105 of the physical block to which the logical block is newly allocated. Then, after the count information is written in the redundant area 105 of the physical block, the count value is counted up.

  Furthermore, at a predetermined timing (in the above example, every time the count value increases by n × k), a physical block in which data with low rewrite frequency is stored is searched. In this search process, a physical block in which count information indicating a value that is greater than or equal to a predetermined value from a value of a portion indicating count information of the count value managed by the counter function (that is, the upper 3 bytes) is stored. The physical block in which data with a low rewrite frequency is stored is considered, and the corresponding physical block is searched. Only when such a physical block is detected, the data stored in the detected physical block is transferred (copied) to another physical block. That is, according to the present embodiment, wear leveling control including a physical block is performed only when there is a physical block storing data with low rewrite frequency.

  Further, according to the present embodiment, the setting of a condition for searching for a physical block in which data with low rewrite frequency is stored is set in the physical calculated based on the ID information read from the flash memory 2. Since it is automatically performed based on the total number n of blocks, it is not necessary to set conditions by the user.

  Hereinafter, a second embodiment of the present invention will be described. In this case, differences from the first embodiment will be mainly described, and description of common points with the first embodiment will be omitted or simplified.

  In this embodiment, an address conversion table is prepared for each logical zone as shown in FIG. Each address conversion table manages which logical block corresponds to which physical block only for each logical block constituting the corresponding logical zone. In FIG. 6, reference numeral 103-0 is an address conversion table corresponding to a logical zone whose logical zone number (LZN), which is a serial number assigned to the logical zone, is # 0. It is an address conversion table corresponding to the logical zone # 1. Each address conversion table (103-0 and 103-1) includes the LBN of the logical block and the physical block address of the physical block to which the logical block is assigned (for each logical block constituting the corresponding logical zone). PBA) is recorded. For this reason, the size of each address conversion table (address conversion table for each logical zone) is smaller than when all logical blocks are managed by one address conversion table. The address conversion table for each logical zone is stored in different physical blocks. In other words, two or more address conversion tables corresponding to two or more logical zones are not simultaneously stored in the same physical block. For example, the address conversion table 103-0 corresponding to the logical zone of LZN # 0 is stored in the physical block of PBA # 5, and the address conversion table 103-1 corresponding to the logical zone of LZN # 1 is stored in PBA # 1076. Stored in physical block. Hereinafter, the physical block where the address translation table is stored is referred to as a “table storage block”. Each time the address conversion table is updated on the work area 8, as shown in FIG. 6, an area in a physical block (one or more free physical pages or a free area in a physical page) that is a table storage block is stored. Saved. For example, if the address conversion table for each logical zone is set to a size that can be stored in one physical page, and the address conversion table is stored in order from the first physical page every time the address conversion table is updated, The table storage block can store 64 address conversion tables. When 64 address conversion tables are stored in this table storage block and there is no free area in which the address conversion table can be stored, another physical block is allocated as a table storage block. As shown in FIG. 6, the address conversion table 103-1 is stored up to the last physical page # 63 of the physical block of PBA # 1076 which is the table storage block of the address conversion table corresponding to the logical zone of LZN # 1. If there is, there is no empty area for storing the address translation table in the physical block of PBA # 1076. Therefore, if the address translation table 103-1 is updated thereafter, another physical block (empty physical block) is assigned as the table storage block of the address translation table 103-1, and the other physical block is assigned to the other physical block. The updated address conversion table 103-1 is stored. Hereinafter, such a process in which another physical block is allocated as a table storage block is referred to as “a table storage block change”.

  In this embodiment, the memory controller 3 manages information (hereinafter referred to as “table management information”) indicating in which physical block the address translation table corresponding to which logical zone is stored. In the example shown in FIG. 6, the table management information 101 includes information that can determine the correspondence between the LZN of each logical zone and the PBA of the table storage block of the address conversion table corresponding to the logical zone of the LZN. Yes. By referring to this table management information 101, for example, the table storage block of the address translation table 103-0 corresponding to the logical zone of LZN # 0 is a physical block of PBA # 5, or the logical block of LZN # 1 It can be seen that the table storage block of the address conversion table 103-1 corresponding to the zone is a physical block of PBA # 1076. The table management information 101 is stored in any one of two or more preset physical blocks for table management information (hereinafter referred to as “management information block candidates”). In this example, PBA # 0 and PBA # 1 physical blocks (that is, two physical blocks) are set as management information block candidates. Therefore, the table management information is stored in either the physical block of PBA # 0 or PBA # 1. Hereinafter, the physical block of the storage destination of the table management information selected from the management information block candidates (physical blocks of PBA # 0 and PBA # 1) is referred to as “management information block”. The table management information 101 is updated on the work area 8 when the table storage block of the address conversion table corresponding to any logical zone is changed. Each time the table management information 101 is updated on the work area 8, a free area (one or more free physical pages or physical pages in a physical block which is a management information block (for example, a physical block of PBA # 0)) is stored. Saved in free space). If there is no free area that can store the table management information in the physical block, another physical block (for example, a physical block of PBA # 1) of the two management information block candidates is used as the management information block. Assigned. That is, two predetermined physical blocks are alternately used as management information blocks. Hereinafter, this process is referred to as “management information block switching”.

  In this embodiment, when a logical block is newly assigned to a physical block, a rewrite mark is written in the redundant area of the physical block in addition to the logical address information indicating the newly assigned logical block. It is. The “rewrite mark” referred to in the present embodiment is version number information that is updated when a result of processing related to a logical block being newly assigned to a physical block matches a predetermined condition. With respect to “processing related to the logical block being newly assigned to the physical block” and “predetermined condition”, some examples will be described in detail later.

  The rewrite marks are at least three types of information that circulate in a predetermined order. That is, the rewrite mark is updated (transitioned) in a predetermined order, and after the last rewrite mark is reached, it is updated (returned) to the first rewrite mark. For example, as shown in FIG. 7A, every time a predetermined condition is met, the memory controller 3 changes the rewrite mark to the first rewrite mark “55”, the second rewrite mark “5A”, the third rewrite mark, The rewrite mark “A5” and the fourth rewrite mark “AA” are updated in this order, and the next rewrite mark “AA” is updated to the first rewrite mark.

  Hereinafter, the process performed in the present embodiment will be described with reference to FIGS. 7B and 8, taking as an example that the rewrite mark is updated according to the rule described with reference to FIG. 7A. At this time, a period in which the rewrite mark is the first rewrite mark “55” is referred to as “first period”, and a period in which the rewrite mark is the second rewrite mark “5A” The second period ”, the period when the rewrite mark was the third rewrite mark“ A5 ”is referred to as the“ third period ”, and the rewrite mark is the fourth rewrite mark“ AA ”. This period is called “fourth period”. Since the rewrite mark circulates, the period also circulates.

  The physical block in which the first rewrite mark “55” is written is a physical block to which a logical block is newly allocated in the first period, and the second rewrite mark “5A” is written therein. The physical block is a physical block to which a logical block is newly assigned in the second period, and a physical block in which the third rewrite mark “A5” is written is newly added in the third period. The physical block to which the fourth rewrite mark “AA” is written is a physical block to which a logical block is newly allocated in the fourth period.

  Specifically, for example, in FIG. 7B, when a logical block of LBN # 41 is newly assigned to a physical block of PBA # 12 detected as an empty physical block, as shown in (4A), Since the time is within the first period, the LBN “# 41” of the newly allocated logical block and the first rewrite mark “55h” are stored in the redundant area 105 of the physical block of the PBA # 12. Written.

  Next, as shown in (4B), when a logical block of LBN # 42 is newly allocated to a physical block of PBA # 18 detected as an empty physical block, at that time also within the first period Therefore, the LBN “# 42” of the newly allocated logical block and the first rewrite mark “55h” are written in the redundant area 105 of the physical block of PBA # 18.

  After that, as shown in (4C) and (4D), a new logical block is allocated to the physical block. However, since both are within the first period, the physical block to which the new logical block is allocated In the redundant area 105, the LBN of the newly allocated logical block and the first rewrite mark “55h” are written.

  Here, in the case of (4D), that is, when a logical block of LBA # 44 is newly allocated to the PBA # 27 physical block, it is assumed that the result of processing related to the allocation matches a predetermined condition. In this case, the rewrite mark is updated from the first rewrite mark “55” to the second rewrite mark “5A”. At this point, the first period ends and the second period starts.

  Therefore, after that, for example, as shown in (4E), when a logical block of LBN # 45 is newly allocated to a physical block of PBA # 31 detected as an empty physical block, at that time, in the second period Therefore, the LBN “# 45” of the newly allocated logical block and the second rewrite mark “5Ah” are written in the redundant area 105 of the physical block of PBA # 31.

  As described above, the rewrite mark written in the redundant area of the physical block differs depending on in which period the logical block is newly allocated to the physical block.

  The free block search for searching for a physical block to which a new logical block is newly assigned is performed for all physical blocks used as a storage area of the host system 4. At that time, empty blocks are sequentially searched from the first physical block toward the last physical block for all the physical blocks. In this way, for the physical blocks included in the range to be searched, the search for empty blocks in the order from the first physical block to the last physical block is repeatedly performed, so that data that is hardly rewritten (rewrite frequency is If there is no physical block in which (low data) is stored, the number of rewrites of the physical block included in the search target range is expected to be substantially equal.

  Now, the memory controller 3 has not been rewritten at a predetermined timing (for example, when the rewrite mark is updated) for at least one period (writing after the stored data is once erased). A physical block, in other words, a physical block that has passed a period longer than at least one period from the allocation of the currently allocated logical block is searched.

  For example, a physical block that has not been rewritten for longer than one period is searched. In this case, a physical block in which a rewrite mark corresponding to a period two or more periods before the current period is stored is searched. As shown in FIG. 8, if the current rewrite mark is the second rewrite mark “5Ah”, the current period is the second period. Therefore, the physical block in which the fourth rewrite mark “AAh” or the third rewrite mark “A5” is stored is written in the first period, which is one period before the second period. It is a physical block that has not been replaced. Therefore, if the current rewrite mark is the second rewrite mark “5Ah”, the fourth rewrite mark “AAh” or the third rewrite mark that is in the order before the first rewrite mark “55”. The physical block in which the rewrite mark “A5” is stored is searched. That is, in the example of FIG. 8, physical blocks PBA # 6, # 15, and # 16 are detected as physical blocks that have not been rewritten for longer than one period.

  In the present embodiment, a physical block that has not been rewritten for a period longer than one period is regarded as a physical block in which data with a low rewrite frequency is stored. When such a physical block is detected, the memory controller 3 performs a free block search to detect another physical block (empty block), and a physical block that is considered to store data with a low rewrite frequency. Is transferred (copied) to another physical block. Furthermore, the memory controller 3 writes the current rewrite mark in the other physical block. Specifically, for example, as shown in (5A), (5B), and (5C) of FIG. 8, the data stored in the detected physical blocks of PBA # 6, # 15, and # 16 is empty. Transferred (copied) to the physical blocks PBA # 32, # 33 and # 34 detected by the block search. In addition, LBN # 6, # 15, and # 16 are written as logical address information in the redundant area 105, and the second rewrite mark “5Ah” that is the current rewrite mark is written as PBA # 32 as the rewrite mark. , # 33 and # 34 are written.

  After this transfer process is completed, the data stored in the transfer source physical block is erased. Specifically, an internal command instructing to erase data stored in the physical blocks of PBA # 6, # 15, and # 16 is sequentially given from the memory controller 3 to the flash memory 2, and the internal command In response, the flash memory 2 erases the data stored in the physical blocks of PBA # 6, # 15 and # 16.

  It should be noted that the criteria for considering data with low rewrite frequency as stored physical blocks, that is, for how long a physical block that has not been rewritten for longer than that is considered as a physical block with low rewrite frequency stored, It can be set as appropriate in consideration of the number of periods (and / or the length of one period) until the rewrite mark is completed.

  In addition, when the number of periods until the rewrite mark is completed is small, when the rewrite mark is updated, the physical block in which the same rewrite mark as the changed rewrite mark is written in the period before the rewrite mark Care must be taken that there is no remaining. Specifically, the memory controller 3 searches for a physical block that has not been rewritten for longer than one period, and transfers (copies) data stored in the detected physical block to another physical block. It is necessary to complete the processing by the next time the rewrite mark is updated. In order to ensure this management, the memory controller 3 stores the data stored in the physical block in which data with low rewrite frequency is stored until there is no physical block that has not been rewritten for longer than one period. The transfer process may be prioritized so that commands from the host system 4 are not accepted.

  The current rewrite mark is stored in, for example, a storage area in the memory controller 3, for example, a work area 8 (a volatile memory such as SRAM). The rewrite mark stored in the work area 8 is copied (written) to the flash memory 2 at an appropriate time. When the power is turned off, the rewrite mark stored in the work area 8 is erased, but when the power is turned on, the rewrite mark stored in the flash memory 2 is read into the work area 8. Thereafter, the rewrite mark is used as the current rewrite mark. The memory controller 3 may be provided with a storage area composed of a nonvolatile RAM such as a FeRAM (Ferroelectric Random Access Memory) or MRAM (Magnetic Random Access Memory), and a rewrite mark may be held in this storage area. When the rewrite mark is held in such a nonvolatile RAM, the rewrite mark can be managed on the nonvolatile RAM, and it is not necessary to copy the rewrite mark to the flash memory 2.

  In addition, a physical block regarded as a physical block in which data with low rewrite frequency is stored is erased after the data stored in the physical block is transferred (copied) to another physical block, It is considered as an empty physical block. There is a possibility that the physical block that has been made empty has a small number of rewrites up to that point. Conversely, the physical block that is the data copy destination may have a large number of rewrites up to that point, but the data with a low rewrite frequency may be copied, which may reduce the number of subsequent rewrites. Get higher. Based on such a principle, it can be expected that the number of rewrites of a plurality of physical blocks in the flash memory 2 is equalized.

  Hereinafter, an outline of the flow of processing performed in the present embodiment will be described with reference to FIG.

  First, initial setting is performed (step 1101). For example, the memory controller 3 sets the current rewrite mark.

  When a write command is received from the host system 4 after the initial setting, the memory controller 3 needs to newly set a physical block corresponding to the logical block to which the logical access area specified by the write command belongs. Is determined (step 1102). If this is necessary (YES in step 1102), a free block search is performed, and a logical block to which the logical access area designated by the write command belongs is allocated to the detected free block (step 1103). Specifically, the LBN of the logical block to which the logical access area designated by the write command and the current rewrite mark are written in the redundant area 105 of the detected empty block (physical block). The processing related to newly assigning a logical block to a physical block is also executed in this step 1103. If the result of the process matches a predetermined condition, the rewrite mark is updated, and if the result does not match the predetermined condition, the rewrite mark is not changed.

  The memory controller 3 determines whether or not the rewrite mark has been updated in step 1103 (step 1104), and if it has been updated (YES in step 1104), search processing of the physical block in which data with low rewrite frequency is stored. I do. When a physical block storing data with low rewrite frequency is detected, the memory controller 3 performs a data transfer process for copying the data stored in the detected physical block to another physical block ( Step 1105). Specifically, a physical block that has not been rewritten for a period longer than one period is searched, and when such a physical block is detected, the data stored in the detected physical block is another physical block. Forwarded to After this transfer is completed, the data stored in the detected physical block is erased.

  According to the above description, when a logical block is newly assigned to a physical block, a rewrite mark is written to the physical block. The rewrite mark is version number information that is updated when a result of processing related to a logical block newly assigned to a physical block matches a predetermined condition. A physical block in which a rewrite mark two or more orders before the rewritten mark after the update is stored is regarded as a physical block in which data with a low rewrite frequency is stored. The wear leveling control including the physical block is performed only when there is a physical block storing such data with low rewrite frequency.

  As described above, the rewrite mark is version number information that is updated when a result of processing related to a new allocation of a logical block to a physical block matches a predetermined condition. Any of the following first to fourth examples can be adopted as a process related to a new allocation of a logical block to a physical block and a predetermined condition. Hereinafter, each example will be described in detail.

  <First example>.

  In the first example, “a process related to a logical block being newly assigned to a physical block” means a count value (hereinafter, referred to as the number of changes of the physical block (table storage block) of the storage destination of the address translation table). (Referred to as “change count value”) is counted up (or counted down), and “predetermined condition” is that the change count value becomes a predetermined value.

  The change count value is counted up (or counted down) every time the table storage block is changed. The changed count value after counting up (or after counting down) is written to the table storage block. Thereby, it is possible to grasp how many times the table storage block has been changed from the change count value stored in the table storage block. As described above, since the change count value is written in the table storage block instead of the rewrite mark, the data given from the host system is stored in the flash memory 2 as shown in FIG. 10A. Existing physical blocks (hereinafter referred to as “data storage blocks”) and table storage blocks (physical blocks of PBA # 5 and PBA # 14) in which the address translation table is stored are mixed. If the rewrite mark and the change count value are set so as not to overlap, the physical block is a data storage block depending on whether the rewrite mark is written or the change count value is written. Or a table storage block. For the data storage block, information indicating that the data storage block is stored (information indicating which logical zone's address conversion table is stored) may be written instead of the logical address information.

  In this first example, it is determined in advance how many times the table storage block is changed to update the rewrite mark. That is, a predetermined value for the change count value is set in advance. When the table storage block is changed, the change count value is counted up (or counted down). When the changed count value after the count up (or count down) reaches a predetermined value, the rewrite mark is updated. The For example, when the predetermined value is 15 (0Fh), the rewrite mark is updated when 15 (0Fh) is written as the change count value in the newly allocated table storage block. In the case of the present embodiment, if the change count value is returned to 15 (0Fh) and then 0 (00h), the rewrite mark and the change count value will not overlap.

  Note that it is possible to appropriately set which logical zone's address conversion table is to be updated based on the change count value of the table storage block in which the address conversion table is stored. Further, the current rewrite mark may be stored in the table storage block.

  Hereinafter, the flow of processing relating to the first example will be described.

  For example, the memory controller 3 executes the process shown in FIG. 10B in S103 of FIG. In other words, when the address change table is updated by newly assigning a logical block to a physical block, the memory controller 3 can store the updated address conversion table in the physical block that is a table storage block. It is determined whether or not a physical page remains (S1111).

  If it is a determination result that it does not remain (S1111: YES), the memory controller 3 executes S1112. That is, the memory controller 3 searches for another physical block (empty block) by searching for a free block, and uses the detected other physical block as a new table storage block (that is, changes the table storage block). Further, the memory controller 3 reads the change count value stored in the physical block that was the table storage block before the change from the physical block, and counts up (or counts down) the change count value. Then, the memory controller 3 writes the changed count value after the count-up (or after the count-down) and the updated address conversion table in the other physical block (empty block) that is the table storage block after the change. Further, the memory controller 3 updates the PBA corresponding to the LZN of the logical zone corresponding to the address conversion table in the table management information 101 (see FIG. 6) to the PBA of the changed table storage block.

  Thereafter, the memory controller 3 determines whether or not the changed count value after counting up (or counting down) is a predetermined value (S1113). If the change count value is a predetermined value (S1113: YES), the memory controller 3 updates the rewrite mark (S1114).

  The above is the description of the first example. The current rewrite mark is preferably stored in the flash memory 2 or the nonvolatile RAM.

  <Second example>.

  In the second example, “processing related to a logical block being newly assigned to a physical block” is a count value (hereinafter, referred to as the number of times of switching of a physical block (management information block) as a storage destination of table management information. (Referred to as “switch count value”) is counted up (or counted down), and “predetermined condition” is that the switch count value becomes a predetermined value.

  The switching count value is counted up (or counted down) every time the management information block is changed. The switching count value is written in the management information block. Thereby, it is possible to grasp how many times the management information block is switched from the switching count value stored in the management information block.

  The management information block is selected from management information block candidates. In the example shown in FIG. 11A, physical blocks PBA # 0 and PBA # 1 are management information block candidates. Therefore, the physical block of PBA # 0 or PBA # 1 is used as the management information block. The current rewrite mark may be written in this management information block.

  In this example, the physical block of PBA # 0 or PBA # 1 is not assigned to the table storage block or the data storage block. Further, it is not necessary to write the change count value in the table storage block.

  In this second example, it is determined in advance how many times the management information block is switched to update the rewrite mark. That is, a predetermined value for the switching count value is set in advance. When the management information block is switched, the switching count value is counted up (or counted down). When the switching count value after counting up (or counting down) reaches a predetermined value, the rewrite mark is updated. The The predetermined value may be one or plural (for example, a multiple of a certain natural number).

  Hereinafter, the flow of processing relating to the second example will be described.

  For example, the memory controller 3 executes the process shown in FIG. 11B in S1103 of FIG. That is, when the memory controller 3 updates the table management information in accordance with the change of the table storage block, a free physical page that can store the updated table management information remains in the physical block that is the management information block. It is determined whether or not (S1121).

  If it is a determination result that it does not remain (S1121: YES), the memory controller 3 executes S1122. That is, the memory controller 3 sets the other physical block of the two management information block candidates described above as a new management information block (that is, switches the management information block). Further, the memory controller 3 reads the switching count value stored in the physical block that was the management information block before switching from the physical block, and counts up (or counts down) the switching count value. Then, the memory controller 3 writes the switching count value after counting up (or after counting down) and the updated table management information in the other physical block that is the management information block after switching.

  Thereafter, the memory controller 3 determines whether or not the switching count value after counting up (or counting down) is a predetermined value (S1123). If the switching count value is a predetermined value (S1123: YES), the memory controller 3 updates the rewrite mark (S1124).

  The above is the description of the second example. The current rewrite mark is preferably stored in the flash memory 2 or the nonvolatile RAM.

  <Third example>.

  In the third example, “a process related to a logical block being newly assigned to a physical block” is a search for a free block performed in the order from the first physical block to the last physical block. The “condition” is that the search for empty blocks has been completed. A free block search is a complete search for a free block that starts from the first physical block and goes back to the last physical block.

  For example, the memory controller 3 executes the process shown in FIG. 12A in S1103 of FIG. That is, the memory controller 3 updates the rewrite mark (S1132) when the search for the empty block is completed (S1131: YES).

  The current rewrite mark is preferably stored in the flash memory 2 or the nonvolatile RAM. Further, it is preferable that the search start block (physical block for starting the next search) in the search for the empty block is also stored in the flash memory 2 or the nonvolatile RAM. In the third example, the predetermined condition is that the search for the empty block has been completed. However, the predetermined condition is that the circulation is not limited to a single cycle, and the predetermined number of cycles may be two or more. . In this case, on the work memory (SRAM) 8, the count value indicating the number of cycles for searching for an empty block is updated every time an empty block search is completed. This number of circulations is also preferably stored in the flash memory 2 or the nonvolatile RAM.

  <Fourth example>.

  In the fourth example, “processing related to a logical block being newly assigned to a physical block” means a count value indicating the number of times a logical block is newly assigned to a physical block (hereinafter referred to as “allocation count value”). ”) Is counted up (or counted down), and the“ predetermined condition ”is that the assigned count value becomes a predetermined value.

  The allocation count value is counted up (or counted down) every time a logical block is newly allocated to a physical block. Therefore, it is possible to grasp how many times a logical block is newly allocated to the physical block from the allocation count value.

  In the fourth example, it is determined in advance how many times a logical block is newly assigned to a physical block when the rewrite mark is updated. That is, a predetermined value for the allocation count value is set in advance. The predetermined value may be one or plural (for example, a multiple of a certain natural number).

  For example, the memory controller 3 executes the process shown in FIG. 12B in S1103 of FIG. That is, when a logical block is newly allocated to a physical block, the memory controller 3 counts up (or counts down) the allocation count value, for example, on the work memory (SRAM) 8 (S1141). Then, the memory controller 3 determines whether or not the assigned count value after counting up (or counting down) has reached a predetermined value (S1142). If the allocation count value is a predetermined value (S1142: YES), the memory controller 3 updates the rewrite mark (S1143).

  The above is the description of the fourth example. The current rewrite mark and the assigned count value are preferably stored in the flash memory 2 or the nonvolatile RAM. Further, the allocation count value may be written in a physical block to which a new logical block is allocated.

  As mentioned above, some embodiment of this invention mentioned above is the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to those embodiment. Those skilled in the art can implement the present invention in various other modes without departing from the gist of the present invention.

  For example, in the first embodiment, the timing for searching for a physical block in which data with low rewrite frequency is stored may not be every time the count value increases by n × k. For example, the timing for searching for a physical block May be provided, and based on the table, the timing for searching for a physical block storing data with low rewrite frequency may be determined. As an example of this table, there is a table describing the number of physical blocks and the search timing corresponding to the number (for example, when the number of physical blocks is 512, every time the count value increases by 4096).

  For example, in the second embodiment, the memory controller 3 may select any one of the first to fourth examples and update the rewrite mark based on the selected example. Specifically, for example, the memory controller 3 has a first mode in which the rewrite mark is updated under conditions based on the first example, and a second mode in which the rewrite mark is updated under conditions based on the second example. And a third mode in which the rewrite mark is updated under the condition based on the third example, and a fourth mode in which the rewrite mark is updated under the condition based on the fourth example. May be selected from the first to fourth modes in accordance with an instruction from or a result of an event that has occurred, and the rewrite mark may be updated in accordance with the selected mode.

  Note that the physical blocks that are the targets of the wear leveling control (hereinafter referred to as the present wear leveling control) performed in the above-described embodiment are stored, not all the physical blocks that constitute the flash memory 2. It may be limited by the LBA range of the data. That is, the physical block that is the target of the wear leveling control may be limited by the range of the logical block number (LBN) of the logical block assigned to each physical block.

  In addition, the range of LBA targeted for this wear leveling control (hereinafter referred to as “target LBA range”) or the range of LBA not targeted (hereinafter referred to as “non-target LBA range”) is determined by an instruction from the host system 4. It may be set.

  When such a setting is performed, it is preferable that information relating to the setting is stored in the flash memory 2 and read and held by the memory controller 3 at the time of activation. For example, the memory controller 3 stores information indicating the target LBA range or the non-target LBA range instructed from the host system 4 in a storage area (for example, a work memory 8 or a register in the microprocessor 6) included in the memory controller 3. Hold. Based on the information, the memory controller 3 specifies a logical block (hereinafter referred to as a target logical block) to be subjected to the wear leveling control, and only the physical block to which the target logical block is assigned is stored. A physical block to which a logical block that is not subject to the wear leveling control (hereinafter referred to as a non-target logical block) is assigned as a target of wear leveling control is not subject to the wear leveling control. That is, in the process of detecting a physical block in which data with a low rewrite frequency is stored based on the count information or the rewrite mark (version number information), only the physical block to which the target logical block is assigned is processed. Become a target. On the other hand, a physical block to which a non-target logical block is allocated is a physical block for which it is determined that data with low rewrite frequency is stored based on count information or rewrite mark (version number information). However, it is not detected as a physical block in which data with low rewrite frequency is stored.

  When the target LBA range is instructed from the host system 4, logical blocks included in the LBA range are subject to the wear leveling control, but logical blocks not included in the LBA range are subject to the wear leveling control. Not subject to When a non-target LBA range is instructed from the host system 4, logical blocks included in the LBA range are not subject to the wear leveling control, but logical blocks not included in the LBA range are not subject to the wear leveling. It becomes the object of control. It should be noted that whether or not a logical block whose part is included in the target LBA range and the other part is included in the non-target LBA range is the target of this wear leveling control can be appropriately set. In other words, whether or not the logical block corresponding to the LBA range including both the target LBA range and the non-target LBA range is the target of this wear leveling control can be appropriately set. For example, depending on which ratio of the target LBA range and the non-target LBA range among the LBA ranges corresponding to the logical block is larger, the memory controller 3 determines whether the logical block is the target of the wear leveling control. It may be determined automatically. Specifically, for example, a logical block having a target LBA range larger than the non-target LBA range is a target of the wear leveling control, and a logical block having a non-target LBA range larger than the target LBA range is Not subject to leveling control.

  In addition, the wear leveling control performed in the above-described embodiment is stored in a physical block when a physical block storing data with low rewrite frequency is detected based on count information or a rewrite mark. We explained the wear leveling control that transfers existing data to another physical block. In this wear leveling control, when a physical block storing data with low rewrite frequency is detected, the data stored in the physical block is changed to another physical block based on the number of times the physical block has been erased. It may be further determined whether or not to transfer to. That is, even if the memory controller 3 detects a physical block in which data with a low rewrite frequency is stored based on the count information or the rewrite mark, the memory controller 3 stores the physical block on the basis of the erase count of the physical block. The stored data may be finally determined not to be transferred to another physical block.

  The reason for adding such secondary determination (hereinafter referred to as “transfer source determination”) is that a physical block in which data with low rewrite frequency is stored is detected based on count information or a rewrite mark. This is because it may not be preferable to transfer data stored in the physical block to another physical block. For example, even if a physical block stores data with low rewrite frequency, it is preferable not to transfer the data stored in the physical block to another physical block if the physical block is erased a lot There is. In order to avoid such undesired data transfer, the physical block erase count is compared with the reference erase count, and if the physical block erase count is greater than or equal to the reference erase count, It is preferable to add a transfer source determination that determines that data stored in a physical block is not transferred to another physical block.

  When such a transfer source determination (that is, a determination based on the number of erases of the transfer source physical block) is added, the memory controller 3 creates an erase count table for managing the erase count of each physical block. It is necessary to create and store the erase count table in a flash memory or a non-volatile memory provided separately. Therefore, when a secondary determination based on the number of times of erasing the physical block is added, the microprocessor in the memory controller 3 performs the number of times of erasure as described above based on the program stored in the ROM 12. Control the creation and storage of tables.

  The reference erase count may be a constant value or a changing value. For example, a predetermined ratio of the number of erases guaranteed by the flash memory manufacturer, for example, 90% may be set as the reference number of erases. That is, if the number of erases guaranteed by the flash memory manufacturer is 5000 and the predetermined ratio is 90%, the reference number of erases is 4500. Also, the average erase count and the erase count of the physical block with the maximum erase count (hereinafter referred to as “maximum erase count”) are managed, and the reference erase count is set based on the average erase count or the maximum erase count. It may be set. For example, when the average erasure count is set as the reference erasure count, the memory controller 3 adds the physical block to the physical block only when the erasure count of the physical block storing data with low rewrite frequency is smaller than the average erasure count. The stored data can be controlled to be transferred to another physical block. Further, when a predetermined ratio of the maximum number of erase times, for example, 90% of erase times is set as the reference erase number, the memory controller 3 determines that the erase number of the physical block in which data with low rewrite frequency is stored is the maximum erase number. It is possible to control to transfer the data stored in the physical block to another physical block only when it is smaller than 90% of the erase count.

  By adding such a transfer source judgment based on the number of times of erasure of the transfer source physical block, more accurate wear leveling control can be performed.

  The transfer source determination is based on the number of erasures of a transfer source physical block (a physical block in which data with low rewrite frequency is stored), but instead of or in addition to the transfer source determination, transfer A secondary determination based on the number of erasures of the previous physical block (hereinafter referred to as “transfer destination determination”) may be added. That is, if the erase count of the transfer destination physical block is compared with the reference erase count, and the erase count of the physical block is less than or equal to the reference erase count, the data stored in the transfer source physical block in that physical block A transfer destination determination may be added such that it is determined not to transfer. The reference erase count in the transfer destination determination may be set from the same viewpoint as the reference erase count in the transfer source determination. Further, the reference erase count in the transfer destination judgment and the reference erase count in the transfer source judgment may be the same or different. If the erase count of the transfer destination physical block is equal to or less than the reference erase count, it is preferable to perform a free block search for detecting a physical block having an erase count equal to or greater than the reference erase count. However, if a free block search is continued until a physical block whose erase count is equal to or greater than the reference erase count is detected, the search time may be long. If it is not detected, it is preferable to cancel the empty block search and determine not to transfer the data. The predetermined condition for canceling the empty block search is that when a physical block whose erase count is equal to or greater than the reference erase count is not detected within a predetermined time, or a predetermined number of empty blocks are detected and the erase count is the reference. For example, when there are not more physical blocks than the number of erases.

  Next, processing when the number of times of erasing the transfer source physical block is larger than the number of times of erasing the transfer destination physical block will be described. For this processing, it is necessary to consider the specifications of the flash memory. Commonly used NAND flash memories include those composed of SLC (single level cell) type memory cells and those composed of MLC (multi level cell) type memory cells. is there. Since the data retention period of the flash memory composed of the MLC type memory cells is short, it is necessary to refresh the data stored for a long time. Therefore, when emphasizing data refresh, data transfer is performed even when the erase count of the transfer source physical block is larger than the erase count of the transfer destination physical block, and the life of the flash memory is emphasized. In this case, if the erase count of the transfer-source physical block is larger than the erase count of the transfer-destination physical block, data transfer should not be performed.

  In the case where a virtual block is formed by virtually combining a plurality of physical blocks and the correspondence relationship with the logical block is managed in units of virtual blocks, the virtual block is regarded as one physical block, It is preferable to manage the number of erasures and to search for empty blocks in virtual block units.

DESCRIPTION OF SYMBOLS 1 ... Flash memory system, 2 ... Flash memory, 3 ... Memory controller, 6 ... Microprocessor

Claims (16)

A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Data writing means for writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
Count means for updating a count value every time the logical block is newly assigned to the physical block;
Count information writing means for writing the count information determined based on the count value to the physical block to which the logical block is newly assigned,
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
A part of the plurality of logical blocks, the physical block to which the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range is assigned Whether to transfer the data stored in the physical block to the empty block detected by the empty block search means based on the count value and the count information written in the physical block. A judging means for judging;
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Data writing means for writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
Count means for updating a count value every time the logical block is newly assigned to the physical block;
Count information writing means for writing the count information determined based on the count value to the physical block to which the logical block is newly assigned,
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. Processing target block specifying means for specifying the processing target block;
Whether to transfer the data stored in the processing target block to the free block detected by the free block searching means is based on the count value and the count information written in the processing target block. A judging means for judging;
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When a new table storage block is assigned by the table storage block management means, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. Count information writing means for updating and writing the latest count value that is the updated count value to the physical block newly assigned as the table storage block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
A part of the plurality of logical blocks, the physical block to which the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range is assigned And determining whether to transfer the data stored in the physical block to the empty block detected by the empty block search means based on the version number information written in the physical block. Means,
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When a new table storage block is assigned by the table storage block management means, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. Count information writing means for updating and writing the latest count value that is the updated count value to the physical block newly assigned as the table storage block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. Processing target block specifying means for specifying the processing target block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information Management information storage means to be stored in the block;
Management information block management means for newly allocating another physical block as the management information block when there is no free space for storing the management information in the management information block;
When a new management information block is allocated by the management information block management means, the count value immediately before the count value that matches the count value stored in the management information block in which a free area has disappeared is obtained. Count information writing means for updating and writing the latest count value, which is the updated count value, to the physical block newly assigned as the management information block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
A part of the plurality of logical blocks, the physical block to which the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range is assigned And determining whether to transfer the data stored in the physical block to the empty block detected by the empty block search means based on the version number information written in the physical block. Means,
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Logical block allocating means for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
Address translation table management means for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation means;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management unit Address conversion table storage means for storing the address conversion table;
A table storage block management means for newly allocating another physical block as the table storage block when there is no more free space for storing the address conversion table in the table storage block;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information Management information storage means to be stored in the block;
Management information block management means for newly allocating another physical block as the management information block when there is no free space for storing the management information in the management information block;
When a new management information block is allocated by the management information block management means, the count value immediately before the count value that matches the count value stored in the management information block in which a free area has disappeared is obtained. Count information writing means for updating and writing the latest count value, which is the updated count value, to the physical block newly assigned as the management information block;
Version number information determining means for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
Version number information writing means for writing the version number information determined by the version number information determining means into the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. Processing target block specifying means for specifying the processing target block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Count means for updating the count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version information management means for updating
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
A part of the plurality of logical blocks, the physical block to which the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range is assigned And determining whether to transfer the data stored in the physical block to the empty block detected by the empty block search means based on the version number information written in the physical block. Means,
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Count means for updating the count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version information management means for updating
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Empty block search means for searching for an empty block which is the physical block in the erased state in the flash memory;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. Processing target block specifying means for specifying the processing target block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Means for searching for the physical block in the erased state in the flash memory, the free block searching means for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
Logical block allocation means for allocating the logical block to the physical block in the erased state detected by the free block search means;
Version number information management means for updating the version number information to be written in the physical block to which the logical block is assigned each time the search in the predetermined order in the empty block search means circulates a predetermined number of times,
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
A part of the plurality of logical blocks, the physical block to which the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range is assigned And determining whether to transfer the data stored in the physical block to the empty block detected by the empty block search means based on the version number information written in the physical block. Means,
Data transfer means for transferring data stored in the physical block that is the object of the positive determination to the free block detected by the free block search means when a positive determination is made by the determination means And a memory controller. A memory controller that controls access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
Erasure count management means for managing the erasure count of each of the physical blocks constituting the flash memory;
Block management means for managing a correspondence relationship between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
Means for searching for the physical block in the erased state in the flash memory, the free block searching means for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
Logical block allocation means for allocating the logical block to the physical block in the erased state detected by the free block search means;
Version number information management means for updating the version number information to be written in the physical block to which the logical block is assigned each time the search in the predetermined order in the empty block search means circulates a predetermined number of times,
Version number information writing means for writing the version number information to the physical block to which the logical block is newly assigned;
Information holding means for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. Processing target block specifying means for specifying the processing target block;
Judgment to determine whether or not to transfer the data stored in the processing target block to the free block detected by the free block search means based on the version number information written in the processing target block Means,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching means when a positive determination is made by the determination means And a memory controller. A memory controller according to any one of claims 1 to 10 ,
A flash memory controlled by the memory controller;
A flash memory system. A flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A data writing step of writing data given from the host system side to the physical block corresponding to the logical block to which the area designated by the access instruction belongs;
A count step of updating a count value every time the logical block is newly assigned to the physical block;
Count information writing step for writing count information determined based on the count value to the physical block to which a new logical block is allocated;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
An information holding step for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. A processing target block specifying step for specifying a processing target block;
Whether to transfer the data stored in the processing target block to the free block detected by the free block search step is determined based on the count value and the count information written in the processing target block. A judgment step to judge;
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step A method for controlling a flash memory. A flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A logical block allocation step for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
An address translation table management step for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation step;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management step And an address conversion table storing step for storing the address conversion table;
A table storage block management step for newly allocating another physical block as the table storage block when there is no more free space in the table storage block for storing the address conversion table;
When a new table storage block is assigned by the table storage block management step, the count value immediately before the count value that matches the count value stored in the table storage block that has no free space is obtained. A count information writing step of updating and writing the latest count value, which is the updated count value, into the physical block newly assigned as the table storage block;
A version number information determining step for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
A version number information writing step of writing the version number information determined in the version number information determination step into the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
An information holding step for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. A processing target block specifying step for specifying a processing target block;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step A method for controlling a flash memory. A flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A logical block allocation step for allocating a logical block composed of a plurality of sectors in the logical address space on the host system side to the physical block;
An address translation table management step for managing an address translation table indicating a correspondence relationship between the logical block and the physical block set by the logical block allocation step;
A table storage block that is the physical block that is the storage destination of the address conversion table when the correspondence relationship between at least some of the logical blocks of the address conversion table and the physical block is changed by the address conversion table management step And an address conversion table storing step for storing the address conversion table;
A table storage block management step for newly allocating another physical block as the table storage block when there is no more free space in the table storage block for storing the address conversion table;
When the physical block allocated as the table storage block changes, the management information indicating the physical block allocated as the table storage block is the management information that is the physical block of the storage destination of the management information A management information storage step to be stored in the block;
A management information block management step for newly assigning another physical block as the management information block when there is no more free space in the management information block for storing the management information;
When a new management information block is allocated by the management information block management step, the count value immediately before that is the count value that matches the count value stored in the management information block that has no free space is updated. A count information writing step of writing the latest count value, which is the updated count value, into the physical block newly assigned as the management information block;
A version number information determining step for determining version number information to be written in the physical block to which the logical block is newly allocated based on the latest count value;
A version number information writing step of writing the version number information determined in the version number information determination step into the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
An information holding step for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. A processing target block specifying step for specifying a processing target block;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step A method for controlling a flash memory. A flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A count step of updating a count value each time the logical block is newly assigned to the physical block, and version number information to be written to the physical block to which the logical block is assigned when the count value reaches a predetermined value Version number information management step to update,
A version number information writing step for writing the version number information to the physical block to which the logical block is newly assigned;
A free block search step of searching for a free block that is the physical block in the erased state in the flash memory;
An information holding step for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. A processing target block specifying step for specifying a processing target block;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step A method for controlling a flash memory. A flash memory control method for controlling access to a flash memory that is erased in units of physical blocks based on an access instruction given from a host system,
An erase count management step for managing the erase count of each of the physical blocks constituting the flash memory;
A block management step for managing the correspondence between a logical block composed of a plurality of sectors in the logical address space on the host system side and the physical block;
A search for the physical block in the erased state in the flash memory, and a free block search step for determining in a predetermined order whether or not the physical block in the flash memory is in an erased state;
A logical block allocation step of allocating the logical block to the physical block in the erased state detected in the empty block search step;
A version number information management step for updating version number information to be written in the physical block to which the logical block is allocated each time the search in the predetermined order in the empty block search step circulates a predetermined number of times,
A version number information writing step for writing the version number information to the physical block to which the logical block is newly assigned;
An information holding step for holding information representing a target logical address range or a non-target logical address range specified by the host system;
The physical block to which a part of the plurality of logical blocks and the logical block belonging to the target logical address range or the logical block not belonging to the non-target logical address range are allocated. A processing target block specifying step for specifying a processing target block;
Judgment for determining whether to transfer the data stored in the processing target block to the free block detected by the free block search step based on the version number information written in the processing target block Steps,
Data transfer for transferring data stored in the processing target block to be affirmatively determined to the free block detected by the free block searching step when a positive determination is made in the determination step A method for controlling a flash memory.

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