JP5183662B2 - Memory control device and memory control method - Google Patents

Description

  The present invention relates to a technique for controlling a flash memory, and more particularly to a technique for controlling the execution timing of garbage collection.

  In recent years, flash memories, which are nonvolatile recording media, are used in various electronic devices such as information processing apparatuses such as personal computers, mobile phones and digital cameras. In flash memory, the overwrite operation cannot be performed, so the update data is written to another vacant (unused) sector, and the state (flag) of the sector where the original (pre-update) data was stored is , Updated to “delete”. In the flash memory, data is erased in units of blocks. Therefore, it is necessary to periodically execute a process (garbage collection) in which a write (in use) sector in a block with many “deleted” sectors is moved to another block and used as an unused block.

  In this regard, Patent Document 1 discloses a technique for reducing the variation in the number of erasures for each erasure unit in a management method capable of adapting a flash memory to a file system.

JP-A-9-97218

  However, in the disclosed technique disclosed in Patent Document 1, garbage collection operates independently of an application that uses a file system. Therefore, garbage collection occurs during data writing or reading, thereby increasing the file processing speed. There was a problem that could cause trouble.

  The present invention provides a memory control device and a memory control method capable of reducing the influence on file processing as much as possible by controlling the execution of garbage collection in a flash memory in consideration of the status of file processing and the like. For the purpose.

In order to achieve the above object, a memory control device according to the present invention provides:
A memory control device that controls execution of garbage collection to flash memory,
Sector usage status detection means for checking the usage status of each sector constituting the flash memory and detecting the number of empty sectors;
A file information management means for detecting a processing state of one or a plurality of files stored in the flash memory, and storing and managing the detected processing state in file information generated for each file;
Garbage for determining whether or not it is necessary to execute garbage collection on the flash memory based on the number of empty sectors detected by the sector utilization status detection unit and the processing state of each file detected by the file information management unit The file information managed by the file information management means includes a priority assigned to each file,
The file information management means detects whether or not each of one or a plurality of files stored in the flash memory is currently open,
The garbage collection determining means is a case where the number of empty sectors detected by the sector utilization status detecting means is between a predetermined lower limit value and an allowable value larger than the lower limit value, and the currently open file If there is no file, it is determined that the garbage collection needs to be executed. On the other hand, if there is a file that is currently open, the garbage collection is performed based on the priority assigned to the file. It is characterized by determining whether or not it is necessary to execute .

  According to the present invention, it is possible to secure the free space of the flash memory while reducing the influence on the file processing as much as possible.

It is a block diagram which shows the structure of an electronic device provided with the memory control apparatus which concerns on Embodiment 1 of this invention. FIG. 2 is a diagram schematically showing a memory structure of the flash memory of FIG. 1. It is a block diagram which shows the function structure of CPU (memory control apparatus) of FIG. It is a figure which shows the structure of the file information of Embodiment 1. 4 is a flowchart illustrating a procedure of garbage collection execution processing according to the first embodiment. It is a figure which shows the structure of the file information of Embodiment 2. 10 is a flowchart illustrating a procedure of garbage collection execution processing according to the second embodiment. It is a figure which shows the structure of the copy source information used in other embodiment.

  Hereinafter, a memory control device according to an embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of an electronic apparatus 1 including the memory control device according to the first embodiment. The electronic device 1 is an information processing apparatus such as a personal computer. The electronic device 1 includes a central processing unit (CPU) 11 (memory control device), a read only memory (ROM) 12, a random access memory (RAM) 13, a flash memory 14, an input unit 15, and a display unit 16. And comprising.

  The CPU 11 controls the ROM 12, RAM 13, flash memory 14, input unit 15, and display unit 16 via the bus 17, and accordingly, exchanges data with these.

  The ROM 12 stores various operation programs executed by the CPU 11. The RAM 13 is used as a working memory for temporarily storing operation programs, data, and the like.

  The input unit 15 includes input devices such as a keyboard and a mouse, receives an operation input from the user (for example, an input related to a file operation), and sends the received signal (operation signal) to the CPU 11. The display unit 16 includes a display device such as a CRT or a liquid crystal monitor, and displays data such as characters and images supplied from the CPU 11.

  The flash memory 14 is a non-volatile memory, and includes a register and a memory cell array. The flash memory 14 performs data copying between the register and the memory cell to write or read data.

  The memory cell array includes a plurality of memory cell groups and word lines. Each memory cell group includes a plurality of memory cells connected in series. The word line is for selecting a specific memory cell in the memory cell group. Data is copied between the selected memory cell and the register via the word line, that is, data is copied from the register to the selected memory cell, or data is copied from the selected memory cell to the register. .

  A memory cell constituting the memory cell array is constituted by a MOS transistor having two gates. These two gates are called a control gate and a floating gate, respectively. By injecting charges (electrons) into the floating gate or discharging charges (electrons) from the floating gate, data can be transferred. Writing or erasing of data is performed.

  Since the floating gate is surrounded by an insulator, the injected electrons are held for a long period of time. When electrons are injected into the floating gate, a voltage is applied so that the control gate is on the high potential side. Further, when electrons are discharged from the floating gate, a voltage is applied so that the control gate is on the low potential side.

  Here, a state where electrons are injected into the floating gate is a write state, which corresponds to a logical value “0”. The state in which electrons are discharged from the floating gate is an erased state, which corresponds to a logical value “1”.

  A memory structure of such a flash memory 14 is shown in FIG. The memory area of the flash memory 14 is managed by being divided into “pages” and “blocks”.

  A page is a processing unit in a data read operation and a data write operation performed in the flash memory 14. A block is a processing unit in a data erasing operation performed in the flash memory 14.

  In the flash memory shown in FIG. 2, one page includes a data area of 1 sector (512 bytes) and a redundant area of 16 bytes. There is also a flash memory in which one page is composed of a data area of 4 sectors and a redundant area of 64 bytes. The data area stores data supplied from the CPU 11 during file processing or the like. FIG. 2 schematically shows the memory structure of the flash memory 14. Although not shown, each block has a header area of a predetermined size.

  The redundant area is an area for recording additional data such as an error collection code, a corresponding logical block address, and information (usage flag) indicating the usage status of a page.

  The error collection code is data for detecting and correcting an error included in the data stored in the data area.

  The corresponding logical block address indicates the address of the logical block with which the block is associated when valid data is stored in at least one data area in one block.

  The logical block address is a block address determined based on an address given from the CPU 11. On the other hand, an actual block address in the flash memory 14 is referred to as a physical block address.

  When valid data is not stored in any data area in one block, the corresponding logical block address is not stored in the redundant area included in the block.

  Therefore, by determining whether or not the corresponding logical block address is stored in the redundant area, it is possible to determine whether or not the data of the block including the redundant area has been erased. When the corresponding logical block address is not stored in the redundant area, the block is in a state where data is erased.

  The usage flag indicates the usage status of each sector. For example, “unused”, “moving”, “in use”, “deleted”, and the like are shown. For example, immediately after the block is erased, the utilization flag indicates “unused” in all sectors.

  A block is a unit for erasing the flash memory 14. When data is newly written to the flash memory 14, a plurality of erased (that is, “unused”) sectors corresponding to the size of the data are secured and data is written. When data is overwritten, the data is written in an “unused” sector, and the redundant area of the sector in which the original data is stored is updated. As a result, the use flag of the sector in which the original data is stored is updated to “delete”.

  If data is continuously written to the flash memory 14 by the above method, the usage flag is “deleted” even if the sector actually used (the sector whose usage flag is “in use”) does not increase. "Will increase. Therefore, the CPU 11 needs to return the sector whose usage flag indicates “deleted” to “unused” and appropriately execute a process (garbage collection) for increasing the free space.

  Functionally, the CPU 11 includes an application execution unit 110 and a file system control unit 120, as shown in FIG. The application execution unit 110 executes a predetermined application program (for example, document creation software) stored in the ROM 12. When executing the application program, the application execution unit 110 requests the file system control unit 120 to execute, for example, opening a file, reading / writing data, and deleting a file.

  The file system control unit 120 controls files recorded in the flash memory 14. Specifically, the file system control unit 120 creates a file in the flash memory 14, reads / writes, deletes the file, and the like. In addition, the file system control unit 120 executes garbage collection under a predetermined condition.

  More specifically, as shown in FIG. 3, the file system control unit 120 includes a sector usage status detection unit 121, a file information management unit 122, a garbage collection determination unit 123, and a memory control unit 124.

  The sector usage status detection unit 121 checks the usage status of each sector in the flash memory 14 every predetermined time, detects the number of empty (that is, “unused”) sectors, and expands this on the RAM 13. Store in variable.

  The file information management unit 122 manages information (file information) about the created file. Specifically, as shown in FIG. 4, the file information management unit 122 manages a file information table (developed on the RAM 13) in which file information including a file name and a processing state is entered. To do. When a new file is created, the file information management unit 122 enters the file information of the file in the file information table. Here, the “processing state” is information indicating the current state of the file (for example, “open”, “closed”, etc.), and the file information management unit 122 changes the processing state of the file ( For example, this “processing state” is updated every time “open” → “closed”). When a file is deleted from the flash memory 14, the file information management unit 122 deletes the corresponding file information from the file information table.

  The garbage collection determination unit 123 determines whether or not garbage collection needs to be executed, that is, whether or not garbage collection needs to be executed, every predetermined time. At that time, the garbage collection determination unit 123 refers to the number of empty sectors detected by the sector usage status detection unit 121 and the file information table managed by the file information management unit 122 to determine whether or not garbage collection needs to be executed.

  In this embodiment, when the number of empty sectors is equal to or less than a predetermined lower limit value (for example, the number of sectors in a block (32 in this embodiment)), the garbage collection determination unit 123 needs to execute garbage collection. Judge that there is. In addition, when the number of empty sectors is larger than the lower limit value and is equal to or smaller than a predetermined allowable value (for example, the number of sectors in a block × 2 (64 in the present embodiment)), there is no open file. As long as it is determined that garbage collection needs to be executed. If it is determined that the garbage collection needs to be executed, the garbage collection determination unit 123 requests the memory control unit 124 to execute the garbage collection.

  The garbage collection determination unit 123 determines that the execution of garbage collection is not necessary when none of the above conditions is satisfied.

  The memory control unit 124 accesses the flash memory 14 in accordance with a request from the application program execution unit 110 and executes file creation, file opening, data reading / writing, file deletion, and the like. Further, the memory control unit 124 executes garbage collection in accordance with a request from the garbage collection determination unit 123.

  FIG. 5 is a flowchart showing a procedure of garbage collection execution processing executed by the CPU 11. The garbage collection execution process is started when the user turns on the power to the electronic device 1 and starts up the CPU 11, and periodically repeats the following processing until the power to the electronic device 1 is turned off.

  First, the garbage collection determination unit 123 determines whether or not the number of empty sectors detected by the sector usage status detection unit 121 exceeds the allowable value described above (step S101). As a result, when the number of empty sectors exceeds the allowable value (step S101; YES), the garbage collection determination unit 123 determines that it is not necessary to execute garbage collection. As a result, garbage collection is not executed in the processing loop, and after waiting for a predetermined time (step S105), the garbage collection determination unit 123 executes the process of step S101 described above again.

  On the other hand, when the number of free sectors does not exceed the allowable value, that is, when the number of free sectors is equal to or smaller than the allowable value (step S101; NO), the garbage collection determination unit 123 determines that the number of free sectors exceeds the lower limit value described above. It is determined whether or not there is (step S102). As a result, when the number of free sectors does not exceed the lower limit value, that is, when the number of free sectors is equal to or lower than the lower limit value (step S102; NO), the garbage collection determination unit 123 determines that garbage collection needs to be executed. The memory control unit 124 is requested to execute garbage collection.

  When the memory control unit 124 receives a garbage collection execution request from the garbage collection determination unit 123, the memory control unit 124 executes garbage collection (step S104). Specifically, the memory control unit 124 searches the entire flash memory 14 for a block including the largest number of sectors whose use flag indicates “deleted”, and determines the corresponding block as an erasure target block. Then, the contents (the contents of the data area and the redundant area) of all the sectors in which the use flag in the block to be erased indicates “in use” are copied to empty sectors of other blocks.

  Next, the memory control unit 124 erases all data stored in the erasure target block, and sets the use flags of all sectors in the erasure target block to “unused”. Thus, the garbage collection ends. When there are a plurality of erasure target blocks, the above processing is performed for all erasure target blocks in the garbage collection. As described above, if a plurality of blocks to be erased can be erased, more free space can be secured by executing garbage collection once.

  When the garbage collection ends, after waiting for a predetermined time (step S105), the garbage collection determination unit 123 executes the process of step S101 described above again.

  As a result of the determination in step S102, if the number of empty sectors exceeds the lower limit (step S102; YES), the garbage collection determination unit 123 refers to the file information table to determine whether there is a currently open file. Is determined (step S103). As a result, when there is an open file (step S103; YES), the garbage collection determination unit 123 determines that garbage collection is not necessary, waits for a predetermined time (step S105), and then performs the above-described step S101. Execute the process again.

  On the other hand, if there is no open file (step S103; NO), the garbage collection determination unit 123 determines that the garbage collection needs to be executed, and as a result, the memory control unit 124 executes the above-described garbage collection. (Step S104). When the garbage collection is completed, the garbage collection determination unit 123 executes the process of step S101 described above again after waiting for a predetermined time (step S105).

  As described above, the memory control device (CPU 11) according to the present embodiment does not simply execute garbage collection periodically, but a predetermined condition based on the number of empty sectors and the status of file processing is satisfied. Then, perform garbage collection. In other words, when sufficient free space is secured (when the allowable value is exceeded), garbage collection is not executed, and the lower limit (limit value) is exceeded even if the free space is not sufficient. If this is the case, perform garbage collection only if the file is not open. Thereby, it becomes possible to secure the free space of the flash memory while reducing the influence on the file processing as much as possible.

(Embodiment 2)
Next, a memory control device according to the second embodiment of the present invention will be described. In the memory control device (CPU 11) according to the first embodiment, garbage collection is not executed when any file is open when the free space is between the lower limit value and the allowable value. However, in such a case, the memory control device according to the present embodiment further determines whether or not to execute the garbage collection in consideration of the priority given in advance for each file. The configuration of the memory control device according to the present embodiment is the same as the configuration of the memory control device (CPU 11) according to the first embodiment (see FIG. 3), and the configuration of an electronic device including the memory control device according to the present embodiment is also implemented. The configuration is the same as that of the electronic device 1 according to the first embodiment (see FIG. 1).

  As shown in FIG. 6, the file information management unit 122 according to the present embodiment is expanded on the file information table (RAM 13) in which file information including a file name, a processing state, and a priority is entered. ). Here, the meaning of “processing state” is as described above. The “priority” is indicated by a numerical value, for example, and serves as an index for determining whether or not to execute garbage collection when the file is open when the free space is between the lower limit value and the allowable value. The “priority” may be given to the newly created file by a user input operation via the input unit 15 every time a new file is created, or newly created. Depending on the file type, the file system control unit 120 may automatically assign the newly created file.

  FIG. 7 is a flowchart illustrating a procedure of garbage collection execution processing executed by the CPU 11 of this embodiment. As in the first embodiment, the garbage collection execution process is started when the user turns on the power to the electronic device 1 and starts up the CPU 11, and periodically performs the following processing until the power to the electronic device 1 is turned off. Repeat.

  First, the garbage collection determination unit 123 exceeds the predetermined allowable value (for example, the number of sectors in a block × 2 (64 in the present embodiment)) detected by the sector usage status detection unit 121. It is determined whether or not there is (step S201). As a result, when the number of empty sectors exceeds the allowable value (step S201; YES), the garbage collection determination unit 123 determines that it is not necessary to execute the garbage collection, and after waiting for a predetermined time (step S206), the step The process of S201 is executed again.

  On the other hand, when the number of empty sectors does not exceed the allowable value (step S201; NO), the garbage collection determination unit 123 determines that the number of empty sectors is a predetermined lower limit (for example, the number of sectors in a block (in this embodiment, , 32)) is exceeded (step S202). As a result, when the number of free sectors does not exceed the lower limit (step S202; NO), the garbage collection determination unit 123 determines that garbage collection needs to be executed, and as a result, the memory control unit 124 performs garbage garbage. Collection is executed (step S204).

  On the other hand, when the number of free sectors exceeds the lower limit (step S202; YES), the garbage collection determination unit 123 refers to the file information table to determine whether there is a currently open file ( Step S203). As a result, if there is no open file (step S203; NO), the garbage collection determination unit 123 determines that the garbage collection needs to be executed, and as a result, the memory control unit 124 executes the garbage garbage collection. (Step S204).

  On the other hand, when an open file exists (step S203; YES), the garbage collection determination unit 123 refers to the file information table to acquire the priority of the open file, which is a predetermined criterion. It is determined whether it is smaller than the value (step S205). As a result, when the priority of the file is smaller than the reference value (step S205; YES), the garbage collection determination unit 123 determines that the garbage collection needs to be executed, and as a result, the memory control unit 124 performs garbage garbage. Collection is executed (step S204).

  On the other hand, if the priority of the file is not lower than the reference value, that is, it is equal to or higher than the reference value (step S205; NO), the garbage collection determination unit 123 determines that the execution of garbage collection is not necessary, and waits for a predetermined time. After (Step S206), the process of Step S201 is executed again.

  When the process of step S204 is completed, after waiting for a predetermined time (step S206), the garbage collection determination unit 123 executes the process of step S201 described above again.

  As described above, the memory control device (CPU 11) according to the present embodiment determines whether or not to execute garbage collection in consideration of the priority of the open file. Therefore, the same effect as that of the memory control device of Embodiment 1 can be obtained, and garbage collection can be executed at a timing that is more convenient for the user.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, the condition for determining whether or not to execute garbage collection is not limited to the above embodiment, and the user can set an arbitrary condition for reducing the influence on the file processing as much as possible. For example, in the file system control unit 120, the file information managed by the file information management unit 122 includes information on the sector in which the data of the file is stored in addition to the configuration shown in FIG. 4 or FIG. Also good. In this case, in the garbage collection execution process (see FIG. 7) according to the second embodiment, the garbage collection determination unit 123 sets the erasure target block as an erasure target block even when a low priority file is open (step S205; YES). When the data of the file is stored, it may be determined that it is not necessary to execute garbage collection.

  Further, when there are a plurality of erasure target blocks, the specification may be such that not all erasure target blocks are erased one by one but garbage collection is performed one by one. In this way, a decrease in file processing speed can be further suppressed.

  Further, a countermeasure function in the case where garbage collection is interrupted due to an unexpected power interruption or the like may be added to the memory control device of the above embodiment. In this function, a predetermined area in the header area of each block of the flash memory 14 is used as an area for storing copy source information shown in FIG. The copy source information is used to store information of a copy source sector (a sector in an erasure target block) when garbage collection is executed. As shown in FIG. 8, the copy source information storage area is reserved for the number of sectors in the block (32 in this embodiment), and the copy source information storage area corresponding to sector 0 is sequentially started from the top of the area. , A storage area for copy source information corresponding to sector 1,..., A storage area for copy source information corresponding to sector 31.

  The copy source information is composed of a copy source block number, a copy source sector number, and a copy status. For example, a 4-byte area is secured. The “copy source block number” stores the copy source block number, that is, the block number of the block to be erased at the time of garbage collection. The “copy source sector number” stores the copy source sector number. The “copy status” stores information indicating whether or not copying to the sector (copy destination sector) has been completed at the time of garbage collection.

  When the memory control unit 124 determines a copy destination sector at the time of executing the garbage collection, the “copy source block number”, “copy source sector number”, and “copy status” of the copy source information corresponding to the copy destination sector are determined. , The block number of the block to be erased, the sector number of the copy source, and information indicating that the copy is not completed (hereinafter referred to as “incomplete”) are stored. When the memory control unit 124 writes the contents of the copy source sector to the copy destination sector, the memory control unit 124 displays information indicating that the copy is completed in the “copy status” of the copy source information corresponding to the copy destination sector ( (Hereinafter referred to as “complete”).

  For example, it is assumed that the electronic device 1 is turned off for some reason and the execution of garbage collection is interrupted. In this case, when restarting, since the number of empty sectors is small, the memory control unit 124 executes garbage collection again. When starting the garbage collection, the memory control unit 124 in this example first searches for a block in which “incomplete” is stored in the “copy status” of the copy source information. As a result, if there is a corresponding block, it can be understood that the garbage collection is interrupted while copying the block to the sector corresponding to the copy source information.

  Therefore, in this case, the memory control unit 124 updates the use flag of the sector corresponding to the copy source information to “delete”, searches for a new empty sector, and stores the contents of the copy source sector in the empty sector. make a copy.

  As described above, by securing an area for storing copy source information for each block and using this when executing garbage collection, for example, when garbage collection is interrupted due to an unexpected power failure. Even then, after the restart, garbage collection can be resumed without any problems.

  The present invention can be suitably employed in various electronic devices that use flash memory, such as information processing apparatuses such as personal computers, mobile phones, and digital cameras.

1 Electronic device 11 CPU (memory control device)
DESCRIPTION OF SYMBOLS 110 Application execution part 120 File system control part 121 Sector utilization condition detection part 122 File information management part 123 Garbage collection determination part 124 Memory control part 12 ROM
13 RAM
14 Flash memory 15 Input unit 16 Display unit 17 Bus

Claims (7)

A memory control device that controls execution of garbage collection to flash memory,
Sector usage status detection means for checking the usage status of each sector constituting the flash memory and detecting the number of empty sectors;
A file information management means for detecting a processing state of one or a plurality of files stored in the flash memory, and storing and managing the detected processing state in file information generated for each file;
Garbage for determining whether or not it is necessary to execute garbage collection on the flash memory based on the number of empty sectors detected by the sector utilization status detection unit and the processing state of each file detected by the file information management unit The file information managed by the file information management means includes a priority assigned to each file,
The file information management means detects whether or not each of one or a plurality of files stored in the flash memory is currently open,
The garbage collection determining means is a case where the number of empty sectors detected by the sector utilization status detecting means is between a predetermined lower limit value and an allowable value larger than the lower limit value, and the currently open file If there is no file, it is determined that the garbage collection needs to be executed. On the other hand, if there is a file that is currently open, the garbage collection is performed based on the priority assigned to the file. To determine whether or not to execute
A memory control device. A memory control device that controls execution of garbage collection to flash memory,
Sector usage status detection means for checking the usage status of each sector constituting the flash memory and detecting the number of empty sectors;
A file information management means for detecting a processing state of one or a plurality of files stored in the flash memory, and storing and managing the detected processing state in file information generated for each file ;
Garbage for determining whether or not it is necessary to execute garbage collection on the flash memory based on the number of empty sectors detected by the sector utilization status detection unit and the processing state of each file detected by the file information management unit Collection determination means;
A garbage collection executing means for executing garbage collection when the garbage collection determining means determines that it is necessary to execute garbage collection;
The header area of each block constituting the flash memory is provided with a copy source information area for storing information about a copy source sector at the time of execution of garbage collection, and the garbage collection executing means includes: When the copy-destination sector is determined, the copy source information area corresponding to the copy-destination sector has not been copied as the block number of the block to be erased, the sector number of the copy-source, and the copy status. When the copy is completed, the copy status in the copy source information area is updated to information indicating that the copy is completed.
A memory control device. When the copy source information area stores information indicating that the copy has not been completed, the garbage collection execution unit newly searches for the contents of the copy source sector. Copy to sector,
The memory control device according to claim 2. The file information management means detects whether or not each of one or a plurality of files stored in the flash memory is currently open,
The garbage collection determination unit is configured such that the number of empty sectors detected by the sector usage status detection unit is between a predetermined lower limit value and an allowable value larger than the lower limit value, and there is no currently open file. Determines that it is necessary to execute the garbage collection.
The memory control device according to claim 2 , wherein the memory control device is a memory control device. The lower limit value is the total number of sectors of blocks constituting the flash memory.
The memory control device according to claim 1 , wherein the memory control device is a memory control device. A memory control method for controlling execution of garbage collection to flash memory,
Sector usage status detection step of checking the usage status of each sector constituting the flash memory and detecting the number of empty sectors;
A file information management step of detecting a processing state of one or a plurality of files stored in the flash memory, and storing and managing the detected processing state in file information generated for each file;
Based on the number of empty sectors detected in the sector usage status detection step and the processing status of each file detected in the file information management step, it is determined whether or not it is necessary to execute garbage collection on the flash memory. and garbage collection decision step that, the possess,
The file information managed in the file information management step includes the priority given to each file,
In the file information management step, it is detected whether each of one or a plurality of files stored in the flash memory is currently open,
In the garbage collection determination step, the value of the number of empty sectors detected in the sector usage status detection step is between a predetermined lower limit value and an allowable value larger than the lower limit value, and is currently open. If the file in the file does not exist, it is determined that the garbage collection needs to be executed. On the other hand, if the file currently open exists, based on the priority assigned to the file, Determining whether the garbage collection needs to be executed;
And a memory control method. A memory control method for controlling execution of garbage collection to flash memory,
Sector usage status detection step of checking the usage status of each sector constituting the flash memory and detecting the number of empty sectors;
A file information management step of detecting a processing state of one or a plurality of files stored in the flash memory, and storing and managing the detected processing state in file information generated for each file;
Based on the number of empty sectors detected in the sector usage status detection step and the processing status of each file detected in the file information management step, it is determined whether or not it is necessary to execute garbage collection on the flash memory. A garbage collection determination step,
A garbage collection execution step for executing garbage collection when it is determined in the garbage collection determination step that execution of garbage collection is necessary;
The header area of each block constituting the flash memory is provided with a copy source information area for storing information about a copy source sector at the time of execution of garbage collection, and in the garbage collection execution step, When the copy-destination sector is determined, the copy source information area corresponding to the copy-destination sector has not been copied as the block number of the block to be erased, the sector number of the copy-source, and the copy status. When the copy is completed, the copy status in the copy source information area is updated to information indicating that the copy is completed.
And a memory control method.

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