JP3646679B2 - Non-volatile memory data rewrite method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention shortens the life of a flash memory caused by data rewriting concentrated on the same physical block in a nonvolatile memory such as a NAND flash memory provided in an electronic device such as a memory card. The present invention relates to a data rewriting method for a nonvolatile memory to prevent, and particularly relates to a data rewriting method for a nonvolatile memory which can average the number of times of rewriting related to each physical block using a simple processing method.
[0002]
[Prior art]
In recent years, non-volatile memories such as low-cost NAND flash memory suitable for storing large amounts of data have been widely used in electronic devices such as home appliances, portable electronic devices, and memory cards. FIG. 3 is a diagram illustrating a relationship between a logical block and a physical block related to a storage area of the nonvolatile memory. The storage area of a rewritable flash memory represented by a NAND flash memory is managed in units of blocks, such as erasing data (usually writing binary data “1” to all bits), writing data, etc. Data processing is performed for each physical block.
[0003]
When accessing the flash memory, for example, by referring to an address conversion table stored in a RAM connected to the CPU, the logical block address of the logical block that is the data processing target as shown in FIG. Is converted into a physical block address, and a physical block on which data is erased, written, read, etc. is specified. By adopting a method of accessing by the logical block address in this way, when a defective physical block is generated, the processing operation for the defective physical block is changed to a writable physical block in another erased state for replacement ( Even if it is executed for the empty block (hereinafter referred to as “empty block”), the CPU executing the application program can access using the same logical block address regardless of the presence or absence of block substitution.
[0004]
FIG. 4 is a diagram showing a data structure related to management information stored in a physical block of a conventional flash memory. In FIG. 4, 11 is a data area in which normal data is stored, 12 is a redundant area in which data relating to management information about the physical block is stored, and physical blocks are divided from the data area 11 and the redundant area 12. Composed. Reference numeral 13 denotes a logical block address storage area for storing the address of the logical block corresponding to the physical block having the redundant area, and reference numeral 14 denotes the number of times data is written from the erased state to the physical block having the redundant area. This is a rewrite count storage area for storing (rewrite count). In the logical block address storage area 13, if there is no logical block associated with the physical block, a predetermined value that is not used as the logical block address is written and an empty block is written. It is possible to identify that
[0005]
FIG. 5 is a diagram illustrating an example of an address conversion table configured in a RAM connected to, for example, a CPU in a conventional electronic device including a flash memory. 5A shows an address conversion table before data rewriting when data is rewritten to a logical block having an address L, and FIG. 5B shows an address conversion table after data rewriting. The update of the address conversion table accompanying such data rewriting will be described later. As shown in FIG. 5A, for example, addresses A, B, C, and D of the corresponding physical blocks are stored in the logical blocks specified by the addresses L-1, L, L + 1, and L + 2, respectively. . By referring to the address conversion table as shown in FIG. 5A, the physical block initially associated with the logical block to be processed can be specified.
[0006]
Next, a data rewriting operation performed on a conventional flash memory will be described. First, a schematic procedure of a rewrite operation related to data stored in a predetermined logical block will be described. In order to simplify the description here, as shown in FIG. 3, the address of the logical block to be rewritten is L, which is initially associated with the logical block, and is to be erased along with data rewriting. The address of the physical block (in this way, the physical block associated with the logical block before data rewriting will be referred to as the previously used physical block in the following description) is assigned to B and the logical block. On the other hand, P is the address of a physical block that is newly associated with the data to be written along with data rewriting. In the following description, a logical block and a physical block accessed by an address n are appropriately referred to as a logical block n and a physical block n, respectively.
[0007]
FIG. 6 is a flowchart showing a rewriting method related to data stored in a predetermined logical block. First, the logical block L to be rewritten is specified (step S1). Next, as shown in FIG. 5A, the address B of the previous used physical block associated with the logical block L at that time is specified with reference to the address conversion table (step S2). Next, each physical block in the flash memory is searched to detect a free block and specify the address P of the free block (step S3). Note that a method for detecting an appropriate empty block from a plurality of physical blocks will be described later. As described above, when the physical block P to be written and the physical block B to be erased are specified, data is first written to the physical block P to be written (step S4). Next, the data of the previously used physical block B is erased (step S5). Then, as shown in FIG. 5B, the data rewrite operation is performed by changing the physical block associated with the logical block L from the physical block B to the physical block P in the address translation table (step S6). To complete.
[0008]
Next, a method for detecting an appropriate empty block from a plurality of physical blocks will be described. FIG. 7 is a flowchart showing a method for detecting an appropriate empty block. First, an initial value relating to the minimum number of rewrites is set (step S11). As this initial value, for example, it is conceivable to set the maximum numerical value that can be stored in the rewrite count storage area 14. Next, conceptually, as shown in FIG. 3, with respect to a storage area composed of a plurality of physical blocks arranged sequentially, for example, the physical blocks to be retrieved are retrieved one by one in ascending or descending order with respect to addresses. Specify (step S12). If the physical block to be searched is specified, the logical block address storage area 13 of the physical block is referred to and whether or not the physical block is already associated with the logical block, that is, the physical block is an empty block. It is determined whether or not there is (step S13). When the physical block to be searched is an empty block, it is determined by referring to the rewrite count storage area 14 of the physical block whether the rewrite count of the physical block is smaller than the minimum rewrite count value. (Step S14). If the physical block rewrite count is smaller than the rewrite count minimum value, the search target physical block is set as the write target physical block (step S15), and the rewrite count minimum value of the physical block is set. The number of rewrites is set (step S16).
[0009]
After the process of step S16 is completed, when the physical block that is the search target in step S13 is not an empty block, and when the number of rewrites of the physical block that is the search target in step S14 is greater than or equal to the minimum number of rewrites In step S17, it is determined whether or not the search has been completed for all physical blocks. If the search has not been completed for all physical blocks, the process returns to step S12 and the same processing is performed for the next physical block. When the search is completed for all physical blocks, the number of rewrites related to the physical block is incremented by one in the rewrite count storage area 14 for the physical block finally set as the physical block to be written. Write (step S18).
[0010]
For flash memory such as NAND flash memory, the elements deteriorate when concentration of writing to the same physical block is concentrated. By performing the above processing, the number of rewrites for each physical block is averaged. Thus, the lifetime of the flash memory itself can be extended.
[0011]
[Problems to be solved by the invention]
The conventional free block detection method for averaging the number of physical block rewrites is configured as described above. Therefore, it is necessary to provide a rewrite number storage area for each physical block, and the number of rewrites is large. In such a case, there is a problem that the memory control system becomes complicated because it becomes necessary to perform processing related to wraparound.
[0012]
The present invention has been made to solve the above-described problems, and the number of rewrites for each physical block constituting a nonvolatile memory such as a NAND flash memory can be averaged using a simple method. An object is to obtain a data rewriting method for a nonvolatile memory.
[0013]
[Means for Solving the Problems]
The nonvolatile memory data rewriting method according to the present invention includes a first step of confirming the number of empty blocks that are writable physical blocks in an erased state, and generating a random number to generate a random number of empty blocks. And a second step of selecting one empty block as a physical block to be written.
[0014]
A data rewriting method for a nonvolatile memory according to the present invention comprises a plurality of storage units sequentially arranged by the number of empty blocks, and each storage unit has an empty block registration table in which information for specifying an empty block is stored. A free block to be written is specified by selecting any storage unit in the free block registration table according to the generated random number.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the following description, in order to clarify the correspondence between each means and each step described in the embodiment of the present invention and each means and each step of the invention described in the claims. Each means and each process of the invention described in the claims corresponding to each means and each process described in the embodiment are indicated by parentheses as appropriate.
[0016]
Embodiment 1 FIG.
In the first embodiment of the present invention, the relationship between the logical block and the physical block related to the storage area of the flash memory (nonvolatile memory) has the relationship shown in FIG. 3 as in the prior art. When executing processing related to the data stored in the flash memory, the CPU side accesses by the logical block address. However, the first embodiment is different from the prior art in that it has an empty block registration table for sequentially registering empty block specifying information given as, for example, an address of an empty block. FIG. 1 is a diagram showing an empty block registration table and the like. In FIG. 1, 1 is a free block number counter for recording the number of free blocks, and 2 is a free block registration table composed of a plurality of storage units arranged in sequence. Both the empty block counter 1 and the empty block registration table 2 can be configured in a work area in a RAM connected to the CPU, for example. As shown in FIG. 1, when the number of empty blocks stored in the empty block counter 1 is N, each storage accessible from address 0 to address (N−1) in the empty block registration table 2 Each block stores the address of an empty block.
[0017]
Next, a memory control method according to the first embodiment will be described. A rewrite operation related to data stored in a predetermined logical block is basically the same as the rewrite operation according to the flowchart shown in FIG. The prior art and the present invention have a difference in a method for detecting an appropriate empty block. FIG. 2 is a flowchart showing an appropriate empty block detection method according to the first embodiment of the present invention. First, with reference to the free block number counter 1, the number of free blocks in which data can be written at that time is confirmed (step S21 (first step)). Assuming that the number of empty blocks is N, random numbers are generated in the range of 0 to (N−1) so that an appropriate empty block is selected from the N empty blocks. The address M to be determined is determined (step S22). Next, the address P of the physical block registered in the address M of the free block registration table is read, and this physical block P is specified as the physical block to be written (step S23 (second step)). If the physical block P to be written is specified, the address B of the physical block to be erased along with this write operation is stored in the storage unit of the address M in the free block registration table 2 as shown in FIG. Instead of writing (step S24). As shown in FIG. 6, the processing after the physical block P to be written is specified writes data to the physical block P to be written, erases the data of the previously used physical block B, and converts the address. Data rewriting is completed by updating the table.
[0018]
As described above, according to the first embodiment, step S21 for confirming the number of empty blocks and a random number are generated, and one empty block is selected from a plurality of empty blocks according to the random number. The step S23 for specifying the selected empty block as a physical block to be written is included. Therefore, if the number of times data is rewritten to the flash memory increases, the number of times the physical block is rewritten is also statistically averaged. The number of times each physical block is rewritten by a simple configuration that does not require the rewrite count storage area 14 or the like and a simple method that does not require rewrite count processing, wraparound processing, or the like. As a result, it is possible to extend the life of the flash memory.
[0019]
Also, a free block registration table 2 that stores the addresses of the free blocks is provided in the storage units that are sequentially arranged by the number of free blocks, and any of the storage units in the free block registration table 2 according to the generated random number. Since one empty block to be written is specified by selecting the number of random blocks generated in a predetermined numerical range according to the number of free blocks By associating with the address of the stored storage unit, it is possible to easily construct a system that enables selection of each empty block with approximately the same probability.
[0020]
The data rewriting method for the nonvolatile memory according to the first embodiment is not intended to limit the present invention, but is disclosed for the purpose of illustration. The technical scope of the present invention is defined by the description of the scope of claims, and various design changes can be made within the technical scope described in the scope of claims. For example, it is not always necessary to provide an empty block registration table. Random numbers are generated in a numerical range corresponding to the address range of all physical blocks constituting the storage area of the flash memory, and an address obtained based on the random number is centered. It is also possible to search for physical blocks in the neighboring area and specify a free block closest to the obtained address as a physical block to be written.
[0021]
【The invention's effect】
As described above, according to the present invention, the first step of checking the number of empty blocks and the generation of a random number to select one empty block from a plurality of empty blocks and write the empty block Since the second step of specifying as a target physical block is included, if the number of data rewrites to the nonvolatile memory increases, the number of rewrites of each physical block may be statistically averaged. Non-volatile by averaging the number of rewrites of each physical block with a simple configuration that does not require a rewrite count storage area, etc., and a simple method that does not require rewrite count processing or wraparound processing. This has the effect of extending the life of the memory.
[0022]
According to the present invention, a random number generated by providing a free block registration table that includes a plurality of storage units sequentially arranged by the number of free blocks and in which each storage unit stores information specifying a free block. Depending on the number of free blocks, it is easy to manage the free blocks and to select the storage block in the free block registration table. By associating random numbers generated in a predetermined numerical range with the addresses of the storage units sequentially arranged, it is possible to easily construct a system that allows selection of each empty block with approximately the same probability. Play.
[Brief description of the drawings]
FIG. 1 is a diagram showing an empty block registration table and the like according to Embodiment 1 of the present invention.
FIG. 2 is a flowchart showing an appropriate empty block detection method according to Embodiment 1 of the present invention;
FIG. 3 is a diagram illustrating a relationship between a logical block and a physical block related to a storage area of a nonvolatile memory.
FIG. 4 is a diagram showing a data structure relating to management information stored in a physical block used in a conventional appropriate free block detection method;
FIG. 5 is a diagram illustrating a structure of an address conversion table.
FIG. 6 is a flowchart showing an outline of a data rewriting method used in a nonvolatile memory.
FIG. 7 is a flowchart illustrating a conventional method for detecting an appropriate empty block.
[Explanation of symbols]
1 free block counter, 2 free block registration table, 11 data area, 12 redundant area, 13 logical block address storage area, 14 rewrite count storage area

Claims (2)

A step of specifying a logical block to be rewritten, a step of specifying a physical block to be erased that is initially associated with the logical block in the address translation table, and a step of specifying a physical block to be written Writing data to a physical block to be written, erasing data of a physical block to be erased, and associating a physical block to be written to the logical block in the address conversion table In a data rewriting method of a nonvolatile memory having
A first step of confirming the number of empty blocks that are erasable and writable physical blocks;
A second step of generating a random number, selecting one empty block from a plurality of empty blocks, and specifying the empty block as a physical block to be written, Data rewriting method. A plurality of storage units sequentially arranged as many as the number of empty blocks is provided, and each storage unit is provided with an empty block registration table in which information for specifying an empty block is stored,
2. The data rewriting method for a non-volatile memory according to claim 1, wherein an empty block to be written is specified by selecting one of the storage units in the empty block registration table according to the generated random number. .

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