JP3313576B2 - Memory access control method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile memory (for example,
More particularly, the present invention relates to a memory access control method and apparatus suitable for a flash memory, etc., and more particularly to a memory access control method and apparatus that contributes to an increase in the life of such a non-volatile memory while maintaining data reliability in the event of a power failure.

[0002]

2. Description of the Related Art It is known that a flash memory, which is a non-volatile memory, has a limited number of accesses due to the electrical properties of its storage elements. In particular, in the use of a page memory system in which a storage area of a flash memory is formatted and used as a data storage area composed of a plurality of physical blocks and a data management information storage area for managing the use status of the data storage area. Since the access frequency of the data management area is higher than that of the data storage area,
There is a problem that the memory life is short due to the consumption of storage elements constituting the data management area.

As a countermeasure against such a problem, prior to use of a flash memory, the contents of a data management information storage area of the flash memory are changed to a work memory (a semiconductor having a normal structure) having elements whose access count is not practically limited. It is usually composed of a volatile memory such as an SRAM or a DRAM), and when the memory is in use, the data management information on the work memory is accessed and updated successively. An intermittent rewriting method is conceivable in which the content of the data management information on the flash memory is rewritten with the content of the data management information on the work memory intermittently after the completion of use or at an appropriate time during use.

According to such an intermittent rewriting method of data management information, data writing, reading, erasing, and the like are performed by direct access to a data storage area on a flash memory. Frequent sequential updating is performed by indirect access through access to the management information storage area on the work memory. Therefore, the frequency of access to the data management information storage area on the flash memory is reduced, and the life of the flash memory is reduced. Increase.

[0005]

However, in the above-mentioned intermittent rewriting method, although the contents of data in the flash memory and the contents of data management information in the work memory are updated sequentially, the flash memory is not updated. The contents of the data management information on the memory are updated only intermittently.If the data management information on the work memory is lost due to a power outage or voltage drop of the system power supply during that time, the flash memory In the above, there is a problem that the content of the data and the content of the data management information are left in an inconsistent state, and the flash memory becomes unusable. In particular, this problem becomes remarkable when the flash memory is used as a memory for storing user data of a small portable electronic device such as a PDA. In other words, in this type of small portable electronic device, it is difficult to mount a large capacity battery due to size and weight restrictions, so there is a high possibility that the battery will run out during use. There is a high possibility that a power failure due to poor contact with the battery due to an impact when dropped or the like may occur. If the data and the data management information are inconsistent in the flash memory every time such a battery exhaustion or a power failure occurs and the reliability of the read data is lost, it cannot be put to practical use as a product.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a nonvolatile memory having a limited number of accesses due to the nature of a storage element under the prescribed number of accesses. Provided is a memory access method and device which can be used to the maximum extent and which can guarantee the reliability of data read from the nonvolatile memory thereafter even if a power supply voltage drops or a power failure occurs. It is in.

[0007]

According to a first aspect of the present invention, there is provided a method for controlling a memory access to a nonvolatile memory having a limited number of accesses due to the nature of a storage element, the method comprising: Prior to the start of use of the volatile memory, the data management information stored in the non-volatile memory is copied to a volatile memory having practically no limitation on the number of accesses to obtain data management information for displaying the latest state, Of the physical block status flags and block mapping information constituting the data management information, the physical block status flags are separately copied and stored on the volatile memory as a set, and the physical block status flags for initial status display are stored. And an action for determining that the given memory access request is either an erase request or a write request. A request for determining a physical block mapped to the logical block specified by the memory access request based on the stored block mapping information; and A block use state determination step of referring to a display physical block state flag group to determine that the searched access target physical block is in use; and a physical block state flag group for initial state display, Referring to the latest state display physical block state flag group, an empty physical block search step for searching for a physical block that is empty in the initial state and also empty in the latest state, and the request type determination step The memory access request is determined to be an erase request; and When the access target physical block retrieved by the access target physical block retrieval step is determined to be in use by the block use state determination step, the latest state display physical block state flag of the access target physical block is not used. An erase request executing step of changing the non-volatile memory to the erasure target physical block in the non-volatile memory, and separating the block mapping related to the access target physical block in the block mapping information; Is determined to be a write request, and the access target physical block retrieved in the access target physical block retrieval step is determined to be in use by the block use state determination step, The physical block status flag for displaying the latest status of the target physical block is changed to “not in use” to avoid the write process for the physical block to be accessed in the non-volatile memory. A write request execution step of writing in the free physical block searched in the free physical block search step in the non-volatile memory and separating the block mapping related to the physical block to be accessed in the block mapping information and rebuilding a new block mapping In response to the arrival of the predetermined data management information update request, the content of the data management information in the non-volatile memory is changed based on the content of the data management information for displaying the latest status stored in the volatile memory. A data management information update step to be updated; In the memory access control method characterized by Bei.

According to a second aspect of the present invention, there is provided an apparatus for controlling memory access to a non-volatile memory whose number of accesses is limited due to the nature of a storage element. Before starting,
Data management information stored in the nonvolatile memory,
The number of accesses is copied onto a volatile memory that has no practical limit, and is used as data management information for displaying the latest status. Further, among the physical block status flags and the block mapping information that constitute the data management information, Preprocessing means for separately storing a set of block status flags on the volatile memory to make a physical block status flag group for displaying an initial status; and providing a given memory access request either an erase request or a write request. Access request type determining means for determining that the physical block mapped to the logical block specified in the memory access request based on the stored block mapping information, With reference to the stored initial state display physical block status flag group, The block use state determining means for determining that the searched physical block to be accessed is in use, and the physical block state flags for initial state display and the physical block state flags for latest state display are referred to. An empty physical block searching means for searching for a physical block that is empty in the initial state and empty even in the latest state, and the request type determining means determines that the memory access request is an erasure request and When the access target physical block searched by the target physical block search unit is determined to be in use by the block use state determination unit, the latest state display physical block state flag of the access target physical block is changed to unused. For the physical block to be accessed in the nonvolatile memory. To avoid processed,
And an erasure request execution unit that separates the block mapping related to the access target physical block in the block mapping information, and the access type is determined to be a write request by the request type determination unit, and is searched by the access target physical block search unit. When the access target physical block is determined to be in use by the block use state determination unit, the latest status display physical block status flag of the access target physical block is changed to non-use, and the access in the nonvolatile memory is changed. Avoid write processing to the target physical block,
Instead, the data related to the write request is written to the free physical block searched by the free physical block search means in the nonvolatile memory, and the block mapping related to the access target physical block is separated in the block mapping information. In response to the arrival of a predetermined data management information update request,
A data management information updating unit that updates the content of the data management information in the nonvolatile memory with the content of the data management information for displaying the latest state stored in the volatile memory. Access control device.

Here, in the first or second aspect of the present invention, the “characteristics of the storage element” refers to physical or chemical properties that cause a reduction in the life of the element as the number of accesses increases. In particular, there may be those caused by various causes such as the form of charge accumulation based on the semiconductor structure and the resistance of the wiring material.

Various conditions such as power-on, arrival of a start command from an application or BIOS, and the like can be adopted as the start condition of the “pre-processing step”. In addition, due to the nature of the present invention, it is sufficient that the “data management information” includes at least the physical block status flag group and the block mapping information. However, the scope of the present invention includes other data. It does not exclude cases where information is included. In addition, storing the physical block status flag group for displaying the initial status in a volatile memory (a so-called system memory) having no limit on the number of accesses is purposely performed.
By reading the contents of this stored flag group,
This is so that the initial state can be immediately confirmed without actually reading the contents of the non-volatile memory whose number of accesses is limited. In other words, if the non-volatile memory is accessed each time for checking the initial state, the life of the non-volatile memory (for example, remarkable in the case of a flash memory) is reduced even by the access for reading. This is because The “physical block status flag group” refers to a set of individual status flags indicating whether each physical block in the data storage area of the nonvolatile memory is in the used state or the unused state. Means. Also, "Initial state"
"" Means the state at the time of starting use of the memory or the state at the time of updating the latest data management information after the start of use.

[0011] The meaning of "identification of access request type" is to expect that the possibility of data change in any physical block in a data storage area of a nonvolatile memory (for example, a flash memory) will occur. It is in. It should be noted that “any one” here includes an operation of recognizing whether the request is an erase request or a write request from the relationship with execution of an erase request or write request described later. It will be easily understood.

[0012] Also, "search for physical block to be accessed"
The block mapping information used in (1) is information that specifies a connection relationship between a logical block specified by an access request and a physical block on a non-volatile memory, and can be configured by, for example, a table that defines the relationship between the two. . This connection relationship can be arbitrarily mapped or unmapped (disconnected).

Further, as described above, the "judgment of the block use state" is performed by referring to a group of physical block state flags for displaying the initial state stored in the volatile memory, thereby obtaining the contents of the nonvolatile memory. There is no risk of memory consumption by referring to.

[0014] The meaning of "free physical block search" is to search for a physical block that is free in both the initial state and the latest state. It will be readily understood by those skilled in the art that there will be a function of automatically selecting one of them.

The meaning of "execution of erasure request" means that when a physical block mapped to a logical block according to an erasure request is actually in use, the data of the physical block is not actually erased. This is to virtually erase only on the physical block status flag in the volatile memory. As a result, even when an erasure request arrives, no inconsistency occurs between data and data management information on the nonvolatile memory. In addition, at this time, the mapping between the logical block and the physical block is cut off, so that the data that should have been erased due to the arrival of a read request for the logical block is not erroneously read.

[0016] The term "execute write request" means that when a physical block mapped to a logical block for a write request is actually in use, the data of the physical block is not overwritten and erased. , While virtually overwriting and erasing only the physical block status flag on the volatile memory,
That is, writing to a physical block that is free even in the initial state and the latest state. Thus, even when a write request arrives, no inconsistency occurs between data and data management information on the nonvolatile memory. In addition, at this time, the mapping between the logical block and the physical block up to that point is separated, while a new mapping is established between the actually written physical block and the logical block. When a read request for a block arrives, the overwritten data is normally read, and the data that should have been overwritten and erased is not erroneously read.

Further, "data management information update" means to match the contents of the data management information in the nonvolatile memory with the latest state of the data storage area. Here, the data management information update request may be given from an application program, or means hierarchically lower than the application program (for example, BIO).
S, etc.). The data management information update request is given at a certain cycle cyclically, at an arbitrary timing from an application program, a BIOS, or the like, at an arbitrary timing according to an instruction from an operator, or the like. Various aspects can be taken.
Further, it is conceivable that the period of application of the data management information update request may be appropriately determined according to the usage mode (for example, the writing frequency or erasing frequency) of the electronic device to which the request is applied, the expected power failure frequency, and the like.

It should be noted that, in the description of the above claims, it will be obvious to those skilled in the art that a subsequent erase or write request for a newly mapped logical block arrives as a result of the execution of the write request. Not regulated. It should be noted that, in this case, it is clear that the state of the data storage area in the initial state is not changed in this case, and it is considered that the erasing process or the writing process should be performed as usual. The same applies to a case where a write request for a new logical block that has not been mapped has arrived. In this case, the state of the newly mapped physical block changes to the state of the data storage area in the initial state. Since it is clear that there is no writing process, it is considered that the writing process should be performed as usual. Further, even when a read request for any of the logical blocks arrives, it is clear that the state of the data storage area in the initial state is not changed, and it is considered that the normal write processing may be performed. .

According to the first or second aspect of the present invention, the write processing, the read processing, and the erasure processing can be performed without any trouble on the logical block, while the previous processing can be performed on the physical block. The contents at the time of updating the data management status are retained as they are until the next data management status update, and the consistency between the data and the data management information is maintained. Although the stored data will be lost thereafter, the data already existing at the time of the previous update can be read normally, ensuring the reliability of the data read from the non-volatile memory while minimizing data loss. it can. Moreover, while the data management information on the volatile memory (work memory) is updated sequentially, the data management information on the nonvolatile memory (flash memory, etc.) is updated only intermittently. A non-volatile memory having a limited number of accesses can be used to the maximum extent under the prescribed number of accesses.

[0020]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. As described above, the effect of the memory access control method and device according to the present invention is considered to be remarkable when, for example, a flash memory is used as a memory for storing user data of a small portable electronic device such as a PDA. . That is, in this type of small portable electronic device, it is difficult to mount a large-capacity battery due to size and weight restrictions, so there is a high possibility that the battery will run out during use. In this case, there is a high possibility that a power failure will occur due to poor contact of the battery due to an impact or the like. If the data and the data management information are inconsistent in the flash memory every time such a battery exhaustion or a power failure occurs and the reliability of the read data is lost, it cannot be put to practical use as a product. Such a problem is solved as follows by applying the present invention.

The hardware configuration of a small portable electronic device to which the present invention is applied will be schematically described with reference to the block diagram of FIG. As shown in FIG. 1, a small-sized portable electronic device of this type includes a man-machine interface unit for exchanging data with a user (in recent examples, a pen-touch type input pad or the like is often used). 100)
A user data memory 200 for storing user data such as a telephone directory, a schedule, etc .; a system program memory 300 for storing a system program for realizing various operations of the device; A work memory 400 used as a work area or the like at the time of execution and a CPU 500 for realizing the operation function of the device are schematically constituted. These device components are an address bus, a data bus, System bus 60 including a control bus and the like
They are interconnected by 0. The basic configuration and operation of this type of stored program type control device are well known to those skilled in the art, and thus further description is omitted.

As the user data memory 200, a rewritable flash memory, which is a non-volatile memory having a limited number of accesses due to the nature of the storage element, is used, so that even after the power switch is turned off. The user data is stored. On the other hand, the work memory 400 is a DRA having a rewritable normal semiconductor structure, which is a volatile element.
M, SRAM and the like are used. Therefore, in the state where the power switch is turned on and some operation is being performed, if a power failure occurs due to a battery connection failure due to a battery exhaustion or a drop impact, the work memory 4
00 may be lost.

As shown in FIG. 6, the storage area of the user data memory 200 stores physical block groups B01 to B0.
n and a physical block status flag group F
A storage area for storing 01 to F0n and a storage area for storing block mapping information MAP0 are formatted in advance.

The individual physical blocks constituting the physical block groups B01 to B0n are for storing the individual logical blocks constituting the user data, and have the same size, for example, and have the same size as the logical blocks. The size is the same. Each logical block of the user data that sequentially arrives with the access request includes physical block groups B01 to B0, as described later in detail.
n to be stored.

Physical block status flag group F01 to F0n
Are associated one-to-one with the individual physical blocks constituting the above-described physical block groups B01 to B0n, and each physical block is in use or unused. Is displayed.
Since the physical block status flag groups F01 to F0n are nonvolatile, the physical block group B01 to B0
The usage status of B0n is confirmed by referring to the contents of the physical block status flag groups F01 to F0n. The block mapping information MAP0 is information indicating a connection relationship between a physical block and a logical block, that is, which logical block is stored in each physical block constituting the physical block groups B01 to B0n. Since this block mapping information MAP0 is also nonvolatile, the physical block groups B01 to B0n immediately after the power is turned on.
Is confirmed by referring to the block mapping information MAP0.

In the following description, the physical block status flag groups F01 to F0n and the block mapping information MAP0 are collectively referred to as "data management information".

The reference (reading) and updating (reading and writing) of the data management information are performed by batch reading or writing processing to a series of storage areas storing the data management information because of the necessity of bit processing or the like. Therefore, physical block status flag groups F01 to F01
0n and the frequency of access to the data management information storage area storing the block mapping information MAP0 is significantly higher than the frequency of access to the data storage areas constituting the physical block groups B01 to B0n. Therefore, if the flash memory constituting the user data memory 200 is directly accessed each time to refer to and update the data management information, the data management information storage area is greatly consumed, and the data management area is earlier consumed than the data storage area. Only the data management area reaches its life, and as a result, the life of the entire flash memory is shortened.

Therefore, according to the present invention, as described below, the data management information in the user data memory 200 is copied to the work memory 400, and the data management information is sequentially referenced and updated in order to sequentially update the data management information. While accessing the data management information in the copied work memory 400,
By adopting a method of intermittently updating the data management information in the user data memory 200 with the contents of the data management information in the work memory 400 at an appropriate timing, the problem of shortening the life of the flash memory is solved. ing. In addition, while erasing or rewriting the contents of the data storage area of the user data memory 200 while accessing the data management information in the work memory 400, the data between the data and the data management information in the user data memory 200 may be lost. In order to prevent the occurrence of inconsistency in the user data memory 200, even if an unexpected power outage occurs, the user data memory 200 can be used continuously at the time of power outage recovery, going back to the previous update of the data management information. are doing.

That is, as shown in the general flowchart of FIG. 2 showing the software configuration (configuration of the system program) of the present invention, when the power is turned on to use this apparatus, the user data memory 200 is turned on.
As a pre-process prior to the start of the use of, the physical block status flag groups F01 to F01 configuring the data management information stored in the user data memory (flash memory) 200
F0n and the contents of the block mapping information MAP0 are stored in the work memory 400 as shown in FIG.
The data is copied into the memory and stored as initial values of the latest status display physical block status flag groups F11 to F1n and as initial values of the latest status display block mapping information MAP1 (steps 201 and 202). At this time, the contents of the physical block status flag groups F01 to F0n are further copied and stored in the work memory 400, and stored as the physical block status flag groups F21 to F2n for initial state display ( Step 20
3). The provision of the physical block state flag groups F21 to F2n for displaying the initial state prevents the user data memory 200 from being consumed by directly accessing the user data memory (flash memory) 200 for checking the initial state. That's why.

Thereafter, the present apparatus is in a state of waiting for the arrival of an access request and the arrival of a data management information update request (NO in steps 204 and 205). In this state, if any access request arrives (step 204 YES), the request type is determined (step 206), and the result of the determination is an erase request, a write request,
Depending on which of the read requests is, an erase request execution process (step 207), a write request execution process (step 208), and a read request execution process (step 20)
9) is performed. Thus, while maintaining consistency between the data in the user memory 200 and the data management information, the data management information in the work memory 400 is sequentially accessed, and the erasing process, the writing process, and
A read process will be performed. During this period, for example, when a data management information update request issued by the application program arrives (step 205 YES), FIG.
As shown in (b), the data management information (the physical block status flag groups F11 to F1n and the block mapping information MAP1) in the work memory 400 that has been successively updated up to that point indicates that the user data memory 200 has Data management information (physical block status flag group F01 to
F0n and the block mapping information MAP0) are rewritten (steps 210 and 211), whereby the actual update processing of the data management information in the user data memory 200 is completed. Thereafter, the contents of the physical block state flag groups F01 to F0n immediately after the update are copied into the work memory 400 again (step 203), and the physical block state flag group F21 for displaying a new initial state is displayed.
ＦF2n.

According to the configuration of the present invention shown in the general flowchart of FIG. 2, the data management information in the work memory 400 is sequentially updated every data access, while the user data memory (flash Since the data management information in the memory 200 is updated only intermittently in response to the data management information update request, the frequency of access to the flash memory constituting the user data memory 200 is reduced by that amount, thereby reducing the degree of consumption. Is also reduced, which contributes to an increase in the life of the flash memory.

Next, an erasing process, a writing process, and
The details of each processing will be described in detail while paying attention to the fact that the consistency between the data and the data management information is maintained in the user data memory 200 while the reading processing is normally performed.

The details of the erase request execution process (step 207) will be described with reference to the flowchart of FIG. In the figure, when the process is started, a physical block B0k mapped to the logical block specified by the erase request is searched based on the block mapping information MAP1 in the work memory 400 (step 301). here,
If the physical block B0k mapped to the logical block specified by the erasure request is not found (step 302 NO), a predetermined error process is performed. On the other hand, if such a physical block B0k is found (step 302 YES), then, the physical block status flag group F21 to F21 for displaying the initial status in the work memory 400 is displayed.
By referring to F2n, the use state of the searched physical block B0k in the initial state (state at the time of updating the latest data management information) is checked (step 3).
03).

Here, if it is not in use, the data stored in the physical block B0k has been accumulated since the last update of the data management information and did not exist at the time of the last update of the data management information. This means that even if a power failure occurs after the data is deleted and the data management information cannot be updated, the data (B01 to B0n) and the data management information ( F01 to F0n, MAP0). Therefore, when it is determined that the physical block B0k is not in use (NO in step 304), the data of the physical block B0k is deleted (step 305), and the physical block state flag F1k for displaying the latest state corresponding to the physical block B0k is set to an invalid state. This is changed during use (step 306), and furthermore, the mapping of the physical block B0k in the block mapping information MAP1 is cut off to disable access to the physical block (step 307), and the process ends. In this way, even if a power failure occurs and the data management information cannot be updated, the data that did not exist at the time of the previous update was deleted.
In the above, there is no possibility that inconsistency occurs between the data (B01 to B0n) and the data management information (F01 to F0n, MAP0). After that, when a data management information update request arrives, the contents of the data management information (F11 to F1n, MAP1) on the work memory match the data contents (B01 to B0n) on the data storage area. Therefore, it is possible to update the data management information (F01 to F0n, MAP0) in the user data memory 200 while utilizing the result of the successive data update.

On the other hand, if it is in use, it means that the data stored in the physical block B0k already existed at the time of the previous update of the data management information. If it is impossible to update the data management information due to a power failure, there is a mismatch between the data (B01 to B0n) and the data management information (F01 to F0n, MAP0) on the user data memory 200. May occur. Therefore, when it is determined that the physical block B0k is in use (YES in step 304), the physical block state flag F1k for displaying the latest state corresponding to the physical block B0k is not used without erasing the data of the physical block B0k. Change during (step 30
6) Further, after the mapping of the physical block B0k in the block mapping information MAP1 is separated (step 307), the processing is terminated. In this way, if a power failure occurs and the data management information (F01 to F01)
0n, MAP0) cannot be updated, since the data existing at the time of the previous update is not deleted, the data (B01 to B0n) and the data management information (F01 to F0) are stored in the user data memory 200.
n, MAP0). On the other hand, although the data of the physical block B0k is stored without being erased, since the access to the physical block is performed based on the block mapping information MAP1 on the work memory 400, the data which should have been erased is erroneously read. There is no danger. After that, when a data management information update request arrives, the mapping information MAP0 relating to the physical block B0k is separated from the user data memory 200, and the physical block state flag F0k is not used. Thereafter, when a write request for a new logical block arrives, the physical block B0k can be used as a candidate for a free physical block for storing a new block, although the previous data is stored. .

Next, a write request execution process (step 2)
08) will be described in detail with reference to the flowchart of FIG. In the figure, when the processing is started, a physical block B0k mapped to the logical block specified by the write request is searched based on the block mapping information MAP1 in the work memory 400 (step 4).
01). Here, if such a physical block is found (step 402 YES), then the work memory 40
Physical block status flag group F2 for initial status display in 0
By referring to 1 to F2n, the use state of the searched physical block B0k in the initial state (state at the time of updating the latest data management information) is checked (step 403).

Here, if it is not in use, it means that the data stored in the physical block B0k did not exist at the time of the last update of the data management information. Even if a power failure occurs and the data management information (F01 to F0n, MAP0) cannot be updated, the data (B01 to B0n) and the data management information (F0) remain on the user data memory 200.
01 to F0n, MAP0). Therefore, when it is determined that the physical block B0k is not being used (NO in Step 404), the data of the physical block B0k is overwritten with new data (Step 40).
5) The physical block status flag F1k for displaying the latest status corresponding to the physical block B0k is changed to “in use” (step 406), and the process ends. In this case, if a power failure occurs and the data management information (F01 to F0)
Even if the update of (n, MAP0) becomes impossible, the data that did not exist at the time of the previous update was overwritten and erased, so the data (B01 to B0n) and the data management information ( F01-
F0n, MAP0).
On the other hand, when a data management information update request arrives thereafter, the data management information (F11 to F1
n, MAP1) matches the data contents (B01 to B0n) in the data storage area, so that the data management information (F01) in the user data memory 200 can be utilized while utilizing the results of the data successively updated up to that time. ~ F0
n, MAP0) can be updated.

On the other hand, if it is being used, it means that the data stored in the physical block B0k already existed at the time of the previous update of the data management information. If a power failure occurs and the data management information cannot be updated, the data (B01 to B0) are stored in the user data memory 200.
n) and data management information (F01 to F0n, MAP0) may be inconsistent. Therefore, if it is determined that the physical block B0k is in use (YES in step 404), the data of the physical block B0k is not overwritten and erased.
First, the physical block state flag F1k for displaying the latest state corresponding to the physical block B0k is changed to “not in use” (step 407), and furthermore, the mapping of the physical block B0k in the block mapping information MAP1 is separated to be performed. Is disabled (step 408). Next, by referring to the contents of the physical block status flag groups F11 to F1n for displaying the latest status and the physical block status flag groups F21 to F2n for displaying the initial status, the physical block status flags are currently unused and are not used even in the initial status. The physical block in the state is searched as a free physical block B0j (step 409),
The block mapping information MAP1 is updated by mapping the logical block related to the write request to the free physical block B0j (step 410), and then data is written to the free physical block B0j (step 411). ), The corresponding physical block status flag F1j in the latest status display physical block status flag group F10 to F1n is changed to “in use” (step 4).
12), end the process. In this way, even if a power failure occurs and the data management information cannot be updated, the data (B01) on the user data memory 200 is not deleted because the data existing at the time of the previous update is not deleted. -B0n) and data management information (F01-
F0n, MAP0).
On the other hand, although the data of the physical block B0k is stored without being erased, the access to the physical blocks B01 to B0n is performed based on the block mapping information MAP1 on the work memory 400. Of the logical block that should have been originally written in the physical block B0k can be normally read from the newly mapped physical block B0j. still,
Thereafter, when a data management information update request arrives,
Also in the block mapping information MAP0 on the user data memory 200, the mapping separation for the physical block B0k and the new mapping for the physical block B0j are performed, and the physical block state flag F0k is not used. When a write request for a new logical block arrives, the physical block B0k can be used as a candidate for a free physical block for storing a new block although the previous data is stored.

If the physical block corresponding to the logical block specified by the write request is not found (step 402 NO), it is recognized as a write request for a new logical block, and in this case, the latest state display Physical block status flag groups F11 to F1n and physical block status flag groups F21 to F21 for initial status display
By referring to the contents of F2n, a physical block that is currently in an unused state and is also in an unused state in the initial state is searched as a free physical block B0j (step 413), and the logical block associated with the write request is searched for in this state. The block mapping information MAP1 is updated so as to map to the free physical block B0j (step 414), and then data is written to the free physical block B0j (step 405), and the latest state display physical block state The corresponding physical block status flag F1j in the flag groups F10 to F1n is changed to “in use” (step 406), and the process ends.

Next, a read request execution process (step 2)
09) will be briefly described with reference to the flowchart in FIG. In the figure, when the processing is started, a physical block B0k mapped to the logical block specified by the read request is searched based on the block mapping information MAP1 on the work memory 400 (step 501). Here, if the physical block B0k mapped to the logical block specified by the read request is not found (step 502 NO), a predetermined error process is performed. On the other hand, when such a physical block B0k is found (step 502 YES), data is read from the physical block B0k (step 503). Thus, the physical block group B01
-B0n are all read from the work memory 4
Since the process is performed based on the contents of the block mapping information MAP1 on the E.00, the erase request execution process (step 207) and the write request execution process (step 20) described above.
8) Even if the physical block B0k is left without being erased or overwritten and erased as long as the mapping is canceled in the block mapping information MAP1 on the work memory 400, data from such a physical block B0k is incorrect. Will not be read.

In the present invention described above, the unusable physical blocks left without being erased or overwritten by the erase request execution processing (step 207) and the write request execution processing (step 208) described above are used. Although the number of physical blocks that can actually be used is somewhat reduced due to the presence of B0k, the capacity of this type of flash memory is as large as 1 to 2 Mbytes according to current products, whereas this type of small-sized In general, the amount of user data handled by the electronic device is sufficiently smaller than that, and the unusable physical blocks are restored to a usable state each time the data management information is updated. It is considered that there is no problem in practical use as long as the update period is appropriately designed.

[0042]

FIG. 7 to FIG. 9 show a preferred embodiment of the present invention.
This will be described with reference to FIG. In this embodiment, five physical blocks B01 to B01 are stored in the user data memory 200.
05 is set, and the memory 200
Contains five physical block status flags F01 to F05.
In addition, block mapping information MAP0 that can be mapped to five physical blocks is set. In the work memory 400, five physical block status flags F11 to F15 for displaying the latest status and block mapping information MAP1 that can be mapped to the five physical blocks are set. Further, the work memory 40
In 0, five physical block state flags F21 to F25 for displaying an initial state (a state at the time of turning on the power or updating the previous data management information) are set.

As commonly shown in FIGS. 7 to 9, in the initial state of this embodiment, three physical blocks B01, B02, and B04 are in use (shown by oblique lines in the drawings). It is assumed that two physical blocks B03 and B05 are not used (indicated by white outlines in the figure). Logical blocks B11, B12, and B13 are mapped to the physical blocks B01, B02, and B04, respectively.
Correspondingly, in the block mapping information MAP0, physical block B01 and logical block B11, physical block B02 and logical block B12, physical block B
01 and the logical block B11 are mapped. On the other hand, physical block B03,
For B05, the mapping is released so as not to be linked to any logical block.

Preprocessing (Steps 201, 202, 20)
The state immediately after 3) is shown in FIG. As shown in the figure, immediately after the preprocessing, the user data memory 20
Of course, the contents of the physical blocks B01 to B05 in 0 completely coincide with the contents of the data management information (F01 to F05, MAP0). Also, the user data memory 20
0 and the contents of the block mapping information MAP1 in the work memory 400 completely match. Further, the physical block status flags F01 to F01 to
F05 and the physical block status flags F11 to F15 for displaying the latest status in the work memory 400 and the physical block status flags F21 to F25 for displaying the initial status are completely the same.

FIG. 8 shows a state immediately after the erasure request execution processing (step 207). It is now assumed that an erasure request for the logical block B12 has arrived following the preprocessing. At this time, referring to the latest state display block mapping information MAP1 in FIG.
Is mapped to the physical block B02 (see the arrow A in FIG. 7). Referring to the physical block state flag F22 for displaying the initial state in FIG. 7, it can be seen that the physical block B02 was in use in the initial state (see the position of arrow B in FIG. 7). In this case, the logical block B12 stored in the physical block B02 is not erased (see the arrow A in FIG. 8). Further, the physical block status flag F12 for displaying the latest status is changed to “not in use” (see the position of arrow B in FIG. 8). Further, in the block mapping information MAP1 for displaying the latest state, the physical block B
02 and the logical block B12 are released (see the arrow C in FIG. 8). Therefore, despite the arrival of the erasure request, the data (B01 to B05) in the user data memory 200 and the data management information (F01 to
F05, MAP0), the power failure occurs, and the storage information (F11 to F15,
Even if F21 to F25, MAP1) disappear, access to the user data memory 200 (erasing, writing, reading) will not be hindered. On the other hand, even if a read request for the logical block B12 arrives to read the data that should have been erased by mistake, the mapping for the logical block B12 in the block mapping information MAP1 for displaying the latest state has already been released. It is not determined that an error has occurred, and the contents of the logical block B12 stored in the physical block B02 are not erroneously read. When the data management information update request arrives, the physical block status flag group F0 in the user data memory 200 is stored in the physical block status flag groups F11 to F15 for displaying the latest status and the contents of the block mapping information MAP1.
1 to F05 and the contents of the block mapping information MAP0 are rewritten. Then, the contents of the physical block state flag groups F21 to F25 for displaying the initial state are changed to the physical block state flag groups F01 to F0 of the user data memory 200.
After being updated with the content of No. 5, the data stored in the physical block B02 (the logical block B12) is changed by changing the content of the physical block status flag F22 for displaying the initial status to unused. Is no longer valid, the physical block B02 is treated as if it were empty, and overwriting of arbitrary data is allowed.

Write request execution processing (step 208)
FIG. 9 shows the state immediately after. Now, temporarily, following the pre-processing,
It is assumed that a write request for the logical block B12 has arrived. At this time, referring to the latest state display block mapping information MAP1 in FIG. 7, it can be seen that the logical block B12 is mapped to the physical block B02 (see the arrow A in FIG. 7). Referring to the physical block state flag F22 for displaying the initial state in FIG. 7, it can be seen that the physical block B02 was in use in the initial state (see the position of arrow B in FIG. 7). In this case, the logical block B12 stored in the physical block B02
Is not overwritten (see arrow A in FIG. 9).
Also, the physical block status flag F12 for displaying the latest status
Is changed during non-use (see the arrow B in FIG. 9). Furthermore, block mapping information MAP1 for displaying the latest state
Then, the mapping between the physical block B02 and the logical block B12 is released (see the arrow C in FIG. 9). In addition, the latest status display physical block status flag group F11
To F15 and the physical block state flag groups F21 to F25 for displaying the initial state, the physical block B03 is obtained as the physical block which is in the unused state in the latest state and was also in the unused state in the initial state. Then, the data corresponding to the logical block B12 is written to the obtained free physical block B03 (see the position of arrow D in FIG. 9). Accordingly, the content of the latest status display physical block status flag F13 is changed to “in use”, and at the same time, in the latest status display block mapping information MAP1, a block is set to connect the physical block B03 and the logical block B12. The mapping is established (see the arrow F in FIG. 9). Therefore, despite the overwrite request for the physical block B02, the data (B01 to B05) in the user data memory 200 and the data management information (F01 to F01)
05, MAP0) is maintained. for that reason,
When a power failure occurs, the information stored in the work memory 400 (F11
~ F15, F21 to F25, MAP1) disappear,
Access to the user data memory 200 (erasing, writing, reading) does not hinder. On the other hand, the logical block B1
2, the logical block B1 of the latest state display block mapping information MAP1
2 is mapped to physical block B03,
The latest contents of the logical block B12 stored in the physical block B03 are normally read, and the contents of the logical block B12 stored in the physical block B02 which should have been overwritten and erased are not erroneously read. When a data management information update request arrives, the user data memory 200 is updated with the contents of the latest state display physical block state flags F11 to F15 and the block mapping information MAP1.
The contents of the physical block status flag groups F01 to F05 and the block mapping information MAP0 are rewritten,
Then, the physical block status flag group F for displaying the initial status is displayed.
After the contents of 21 to F25 are updated with the contents of the physical block state flag groups F01 to F05 of the user data memory 200, the contents of the physical block state flags F22 for displaying the initial state are changed to unused. As a result, the data (logical block B12) stored in the physical block B02 is no longer determined to be invalid, the physical block B02 is treated as if it were empty, and overwriting of arbitrary data is permitted. .

[0047]

As is apparent from the above description, according to the present invention, a non-volatile memory having a limited number of accesses due to the nature of the storage element can be used to the maximum extent under the prescribed number of accesses. In addition, even if the power supply voltage decreases or a power failure occurs, the reliability of data read from the nonvolatile memory thereafter is not impaired.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a hardware configuration of a small portable electronic device to which the present invention is applied.

FIG. 2 is a general flowchart showing a software configuration of a small portable electronic device to which the present invention is applied.

FIG. 3 is a flowchart showing details of an erasure request execution process in the general flowchart.

FIG. 4 is a flowchart showing details of a write request execution process in the general flowchart.

FIG. 5 is a flowchart showing details of a read request execution process in the general flowchart.

FIG. 6 is a memory map for explaining a data flow accompanying execution of preprocessing and data management information updating processing.

FIG. 7 is a memory map showing contents of a work memory and a user data memory immediately after execution of preprocessing.

FIG. 8 is a memory map showing contents of a work memory and a user data memory immediately after execution of an erase request.

FIG. 9 is a memory map showing contents of a work memory and a user data memory immediately after execution of a write request.

[Explanation of symbols]

 Reference Signs List 100 Man-machine interface 200 User data memory 300 System program memory 400 Work memory 500 CPU 600 System bus

Claims (2)

(57) [Claims] 1. A method for controlling memory access to a non-volatile memory having a limited number of accesses due to the nature of a storage element, the method comprising: storing data in the non-volatile memory prior to starting use of the non-volatile memory; The data management information is copied to a volatile memory having practically no limit on the number of accesses to obtain data management information for displaying the latest status, and further, a physical block status flag group and block mapping information constituting the data management information A preprocessing step of separately copying and storing a set of physical block status flags on the volatile memory to make a set of physical block status flags for initial status display; and Or an access request type determining step of determining whether the request is a write request, An access target physical block searching step for obtaining a physical block mapped to the logical block specified in the memory access request based on the mapping information, and referring to the stored physical block state flag group for initial state display. A block use state determination step of determining that the searched access target physical block is in use; a physical block state flag group for storing the initial state and a physical block state flag group for displaying the latest state. Referring to, an empty physical block search step for searching for a physical block that is empty in the initial state and also empty in the latest state, and the memory access request is determined to be an erase request by the request type determination step. And the access target physical block search step When the searched physical block to be accessed is determined to be in use by the block use state determination step, the latest state display physical block state flag of the physical block to be accessed is changed to non-use, and the non-volatile memory of the nonvolatile memory is changed. An erasure request execution step of avoiding erasure processing on the access target physical block and separating block mapping of the access target physical block in the block mapping information; and the request type determination step determines that the access request is a write request. When the access target physical block searched in the access target physical block search step is determined to be in use by the block use state determination step, the latest state display physical block of the access target physical block is determined. The status flag is changed to “not in use” to avoid a write process for the physical block to be accessed in the nonvolatile memory. Instead, the data related to the write request is searched for the free physical block in the nonvolatile memory. A write request execution step of writing to the free physical block found in the step and separating the block mapping relating to the access target physical block in the block mapping information and rebuilding a new block mapping; and a predetermined data management information update request arrives A data management information updating step of updating the content of the data management information in the nonvolatile memory with the content of the data management information for displaying the latest state stored in the volatile memory in response to the Memory access control method characterized by Law. 2. An apparatus for controlling memory access to a non-volatile memory whose number of accesses is limited due to the nature of a storage element, wherein the device is stored in the non-volatile memory prior to starting use of the non-volatile memory. The data management information is copied to a volatile memory having practically no limit on the number of accesses to obtain data management information for displaying the latest status, and further, a physical block status flag group and block mapping information constituting the data management information A preprocessing means for separately storing a set of physical block status flags on the volatile memory to obtain a set of physical block status flags for displaying an initial status; and Access request type determining means for determining whether the request is a write request or a write request; Access target physical block searching means for obtaining a physical block mapped to the logical block specified in the memory access request based on the switching information, and referring to the stored physical block status flag group for displaying the initial status. A block use state determining unit that determines that the searched access target physical block is in use; and a physical block state flag group for initial state display and a physical block state flag group for latest state display. Referencing, a free physical block search means for searching for a physical block that is free in the initial state and free even in the latest state, and the request type determination means determines that the memory access request is an erase request, and The access target physical block searched by the access target physical block search unit. Tsu when the click is determined to be in use by the block use state determining means changes the physical block status flag for the latest status of the access target physical block in the non-use,
An erasing request execution unit that avoids an erasing process for the physical block to be accessed in the nonvolatile memory and separates a block mapping related to the physical block to be accessed in the block mapping information; When the access target physical block searched by the access target physical block search unit is determined to be in use by the block use state determination unit, the latest state display physical block state of the access target physical block is determined. The flag is changed to unused so as to avoid the writing process for the physical block to be accessed in the nonvolatile memory, and instead, the data relating to the write request is searched for the free physical block in the nonvolatile memory. A write request execution means for writing to the free physical block searched by the means and for separating the block mapping relating to the physical block to be accessed in the block mapping information and rebuilding a new block mapping; and a predetermined data management information update request arrives Data management information updating means for updating the content of the data management information in the nonvolatile memory with the content of the data management information for displaying the latest state stored in the volatile memory in response to the A memory access control device.