JP3784844B2 - Semiconductor memory device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a semiconductor memory device using a flash memory, and more particularly to control during data writing or erasing.
[0002]
[Prior art]
In recent years, a flash memory, that is, a flash EEPROM has come into practical use as a nonvolatile memory chip, and a semiconductor disk device using the chip has been actively developed.
This flash memory is a kind of EEPROM (electrically erasable, rewritable read-only memory), which can be electrically erased, can be programmed for each byte, and does not require a power supply. It has the advantage that the contents of memory can be guaranteed.
[0003]
[Problems to be solved by the invention]
However, contrary to the above advantages, it has the following disadvantages.
That is, when writing to the memory, overwriting cannot be performed as it is, so it is necessary to erase (write data) every byte after erasing. Here, the unit to be erased differs depending on the chip, but the mainstream is to perform the erase in chip units.
[0004]
Therefore, it has the following problems due to such characteristics.
(1) Since the information of the sub-directory located under the directory of the memory hierarchical structure is on the memory part configured by the flash memory, the file under the sub-directory is deleted or the capacity larger than the current data capacity in the file When writing this data, rewriting of the memory part frequently occurs, and it has been desired to improve the performance in such a case.
[0005]
(2) When deleting a file written in the memory unit, only the directory storage unit for indicating the storage position of the file on the memory unit and the file allocation table (FAT) storage unit are controlled. Since the relevant area itself of the memory section is not erased, if a writing process occurs in this area, the erasing process is required before the writing process, and the performance of the apparatus is degraded. Therefore, a semiconductor memory device that can improve performance even during such writing has been desired.
[0006]
(3) When a logical format is performed on a semiconductor memory device, a specific data pattern on the memory unit is written, so if a writing process to this device occurs thereafter, an erasing process is performed before the writing process. Is indispensable, and the performance as a device is reduced. Therefore, there has been a demand for a semiconductor memory device that does not deteriorate in performance even when a write process occurs after such a logical format is implemented.
[0007]
{Circle around (4)} When overwriting is performed on the memory unit, the performance as a device is deteriorated because it is performed on the area where the corresponding data is written (overwriting). Therefore, there has been a demand for a semiconductor memory device that does not deteriorate in performance even when such overwriting is performed.
[0008]
[Means for Solving the Problems]
A directory storage unit including a memory unit configured by a flash memory, valid information indicating whether data stored in the memory unit is valid or invalid, and a pointer corresponding to the data;
When a file allocation table storage unit indicating a data address of the memory unit corresponding to the pointer of the directory storage unit and an erasure request for arbitrary data in the memory unit are received, the data in the directory storage unit A memory erasure control unit that invalidates the valid information corresponding to the file, rewrites the data pointer in the file allocation table storage unit to an address in a reset state, and erases the data in the memory unit. A semiconductor memory device.
[0013]
[Action]
  BookIn the semiconductor memory device of the invention, when an erasure request is received for any data in the memory unit, the valid information of the corresponding data in the directory storage unit is invalidated, and the corresponding data in the file allocation table storage unit Rewrite the data pointer to the reset address. Then, the data for which the memory unit erase request has been received is erased.
[0014]
  BookIn the semiconductor memory device of the invention, the erase position storage unit stores the position information of the data to be erased in the memory unit, and the memory erase control unit sets the number of data stored in the erase position storage unit in advance. When the threshold value is exceeded, the data in the corresponding memory section is erased.
[0018]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a semiconductor memory device according to Embodiment 1 of the present invention. Prior to this description, a comparative example of the semiconductor memory device will be described.
[0019]
<< Configuration of Semiconductor Memory Device of Comparative Example >>
FIG. 2 is a block diagram showing a configuration of a comparative example of the semiconductor memory device.
In the figure, reference numeral 1 denotes a semiconductor memory device (nonvolatile semiconductor disk device), and 2 denotes a system bus of a host computer (not shown) to which the semiconductor memory device 1 is connected.
The semiconductor memory device 1 includes a host interface unit 3, a processor unit 4, a processor memory unit 5, a flash memory unit 6, a buffer unit 7, a file allocation table (File Allocation TAble) storage unit (hereinafter referred to as a FAT storage unit) 8 , A directory storage unit 9 and an internal bus 10.
[0020]
The host interface unit 3 is a part that performs interface control with a host that is a host device of the semiconductor memory device 1, and the processor unit 4 interprets a command from the host and makes the semiconductor memory device 1 appear to the disk device. This is the part that performs control and the like.
The processor memory unit 5 is a memory in which a program executed by the processor unit 4 is stored.
The memory unit 6 is a storage medium of the semiconductor storage device 1, is configured by a flash memory (FEEPROM), and is divided into blocks in units of erase.
[0021]
The buffer unit 7 is constituted by a byte-accessible volatile memory, and when the data is overwritten on the memory unit 6 as a function, the buffer unit 7 temporarily saves the contents before erasing the memory unit 6. Is.
The FAT storage unit 8 and the directory storage unit 9 have a function for indicating the storage location of data and subdirectory information in the memory unit 6 and are configured by a nonvolatile memory chip such as an EEPROM that can be overwritten in byte units. Has been.
The internal bus 10 is a bus for connecting components in the semiconductor memory device 1.
[0022]
FIG. 3 is an explanatory diagram showing details of the FAT storage unit 8, the directory storage unit 9, and the memory unit 6.
FIG. 4 is an explanatory diagram showing details of the subdirectory shown in FIG.
As shown in these drawings, the storage position of the data in the memory unit 6 or the subdirectory is controlled by the FAT storage unit 8 and the directory unit 9.
[0023]
In the directory part 9, reference numeral 91 denotes a valid information part indicating whether information 92 to 94 described later is valid, where 1 = valid and 0 = invalid.
Reference numeral 92 denotes a storage information identification unit indicating whether the information stored in the memory unit 6 or the currently stored information is data or a subdirectory, where 0 = data, 1 = subdirectory.
Reference numeral 93 denotes a file name identification unit for storing the name of information stored in the memory unit 6, and 94 denotes a pointer to the FAT storage unit 8.
[0024]
Reference numeral 81 in the FAT storage unit 8 indicates a pointer to the memory unit 6.
The memory unit 6 corresponding to the pointer 81 is divided into erase units, and the division unit is called a cluster. Note that 61 in the memory unit 6 indicates the stored information content.
[0025]
Next, data writing in the semiconductor memory device 1 having such a configuration will be described.
Here, an example of file 2 data writing (data capacity is 2 clusters) will be described. In this case, the host first checks the file name identification unit 93 of the directory unit 9 to check whether the file 2 is stored. Here, since the file 2 exists, next, the valid information part 91 and the stored information identification part 92 corresponding to this file name are checked, and it is confirmed that this information is valid data.
[0026]
Next, the pointer 94 is checked to confirm the position of the valid data on the FAT storage unit 8 (in this case, 004H). Then, linking is performed based on the information of the pointer 81 on the FAT storage unit 8. In this case, since the link information is 004H → 005H, the file 2- (1) and the file 2- (2) are stored in the memory unit 6 corresponding to the pointer 81 of the FAT storage unit 8. I understand.
In the information of the pointer 81, “000H” indicates that the information of the corresponding area on the memory unit 6 has no meaning (= reset state address), and “FFFH” indicates that the link in the FAT storage unit 8 is terminated. This is information indicating that the
[0027]
Next, a case where the host writes data in the areas of the file 2- (1) and the file 2- (2), for example, will be described.
In this case, the semiconductor memory device 1 temporarily saves the data in the buffer unit 7, then rewrites the data sent from the host on the buffer unit 7, and at the same time, the corresponding area on the memory unit 6 (in this case) Delete the file 2- (1) and the file 2- (2)), and store the data on the buffer unit 7 in the corresponding region on the memory unit 6.
[0028]
Next, the case of writing data in the file 4 under the subdirectory 1 (data capacity is for one cluster) will be described.
In this case, the host first checks the file name identification unit 93 in the directory part to check whether the subdirectory 1 is stored. In this case, since the subdirectory 1 exists, the valid information section 91 and the stored information identification section 92 are checked next to confirm that this information is a valid subdirectory.
Next, the pointer 94 is checked to confirm the position (in this case, 006H) of the valid subdirectory on the FAT storage unit 8. Next, linking is performed based on the information of the pointer 81 on the FAT storage unit 8. In this case, since the link information is only 006H, it can be seen that the subdirectory 1 is stored in the memory unit 6 corresponding to the FAT storage unit 8.
[0029]
Next, based on the information in the subdirectory 1 (the format is the same as that of the directory storage unit 9), the file storage area is detected based on the above directory information, and the file from this subdirectory is detected. 4 storage areas are detected.
In this case, since the file 4 does not exist, “1” is stored in the valid information section 91a in the subdirectory, “0” is stored in the storage information identifying section 92a, “file 4” is stored in the file name identifying section 93a, and “00AH” is stored in the pointer 94a. Write.
Then, “FFFH” is written in the corresponding pointer 81 (00AH in this case) to the memory unit 6 in the FAT storage unit 8, and finally data is written in the area.
[0030]
Next, the file deletion process will be described.
5 and 6 are explanatory diagrams of the file deletion processing and detailed explanatory diagrams of subdirectories.
When deleting the file 1, the host first checks the file name identification unit 93 of the directory storage unit 9 to check whether the file 1 is stored. In this case, since it is stored, the valid information unit 91 and the stored information identification unit 92 are checked to confirm that this information is a valid file, and the data of the valid information unit 91 indicating the corresponding valid / invalid is invalidated. ("1" → "0").
[0031]
Next, the pointer 94 is checked to confirm the position of the file on the FAT storage unit 8 (in this case, 002H). Then, linking is performed based on the information of the pointer 81 on the FAT storage unit 8. In this case, since the link information is 002H → 003H → 008H, the link information is rewritten to 000H (data in the memory unit 6 is not erased).
[0032]
Next, the case of the logical format for this apparatus will be described.
FIG. 7 is an explanatory diagram for the logical format.
When the host instructs the logical format to the semiconductor memory device 1, the host is instructed to reset all information in the directory storage unit 9 and the FAT storage unit 8 (000H), and then in all areas of the memory unit 6. Gives an instruction to write a specific data pattern.
In response to this instruction, the semiconductor memory device 1 sets all the pointers in the directory storage unit 9 to “000H” and sets all the pointers 81 in the FAT storage unit 8 to “000H”. Then, the memory unit 6 writes a specific data pattern.
The details of the subdirectory in FIG. 7 are the same as those in FIG.
[0033]
Next, examples of the present invention for such comparative examples will be described.
Example 1
FIG. 1 shows Example 1 in the semiconductor memory device of the present invention as described above.
In FIG. 1, 101 is a semiconductor memory device (nonvolatile semiconductor disk device), and 2 is a system bus for connecting the semiconductor memory device 101 to a host (not shown).
[0034]
The semiconductor memory device 101 includes a host interface unit 103, a processor unit 104, a processor memory unit 105, a memory unit 106, a buffer unit 107, a FAT storage unit 108, a directory storage unit 109, an internal bus 110, and a subdirectory storage unit 111. ing.
Here, the host interface unit 103, the processor unit 104, the processor memory unit 105, the memory unit 106, the buffer unit 107, the FAT storage unit 108, the directory storage unit 109, and the internal bus 110 are the host of the semiconductor memory device of the comparative example described above. The interface unit 3, the processor unit 4, the processor memory unit 5, the flash memory unit 6, the buffer unit 7, the FAT storage unit 8, the directory storage unit 9, and the internal bus 10 have the same functions.
[0035]
Similarly to the FAT storage unit 108 and the directory storage unit 109, the subdirectory storage unit 111 is configured by a non-volatile memory chip that can be overwritten in units of bytes, and when a write request to the subdirectory from the host is given, This is a storage unit for storing the write data.
[0036]
Next, processing when a request for writing a new file (file 5, data capacity for one cluster) is made under a new subdirectory (subdirectory 2) will be described.
8 and 9 are explanatory diagrams in this case.
8 and 9, the valid information section 91 to the pointer 94 of the directory storage section 109, the pointer 81 of the FAT storage section 108, the information content 61 of the memory section 106, and the valid information section 91 a to the subdirectory storage section 111. The pointer 94a is the same as each component in FIGS. Further, 95a of the subdirectory storage unit 111 is subdirectory link information indicating a link between the subdirectory storage unit 111 and the FAT storage unit.
[0037]
First, the host checks the file name identification unit 93 of the directory storage unit 109 to check whether or not the subdirectory 2 exists (in this case, it does not exist). Next, the subdirectory name is stored in the file name identification unit 93 and the free space in the FAT storage unit 108 is checked. In this case, since 00BH is empty, “00BH” is written in the pointer 94 and “FFFH” is written in the 00BH pointer 81 in the FAT storage unit 108.
[0038]
Next, when the host stores the sub-directory information at the position of the memory unit 6 corresponding to 00BH of the pointer 81, the present apparatus does not store the sub-directory information in the memory unit 6 but performs as follows.
That is, first, “1” is written in the valid information portion 91a of the subdirectory storage portion 111, “0” is written in the storage information identification portion 92a, “file 5” is written in the file name identification portion 93a, and the subdirectory link information 95a is also written. Write “00BH”, which is link information with the FAT storage unit 108. Then, the address of the corresponding FAT storage unit 108 is written into the pointer 94a as the link information of the subdirectory storage unit 111 (in this case, “00CH”).
Next, the host writes the information of the corresponding memory unit 106 in the FAT storage unit 108 (in this case, “FFFF” in 00CH of the pointer 81), and stores the write data in the corresponding area on the memory unit 6 (this File 5- (1)).
[0039]
As described above, according to the first embodiment, when the subdirectory write request is received, the information is not written on the memory unit 106 as in the comparative example, but the subdirectory storage unit 111 is written. Even when a file under a subdirectory is deleted or a data write having a capacity larger than the current data capacity occurs, rewriting of the memory unit 106 can be suppressed, and thus the performance of the apparatus can be improved.
[0040]
Next, Example 2 will be described.
Example 2
FIG. 10 is a block diagram illustrating the configuration of the semiconductor memory device according to the second embodiment.
In the figure, 201 is a semiconductor memory device (nonvolatile semiconductor disk device), and 2 is a system bus for connecting the semiconductor memory device 201 to a host (not shown).
[0041]
In addition, the host interface unit 203, the processor unit 204, the processor memory unit 205, the memory unit 206, the buffer unit 207, the FAT storage unit 208, the directory storage unit 209, and the internal bus 210 in the semiconductor memory device 201 are the same as the host in the first embodiment. The interface unit 103, the processor unit 104, the processor memory unit 105, the memory unit 106, the buffer unit 107, the FAT storage unit 108, the directory storage unit 109, and the internal bus 110 are configured.
[0042]
Further, the processor unit 204 includes a memory erasure control unit 204a. When this memory erasure control unit 204a receives an erasure request for arbitrary data in the memory unit, the value of the valid information unit 91 corresponding to the data in the directory storage unit 209 is set to “invalid” and stored in the FAT. A data pointer in the unit 208 is rewritten to an address in a reset state, and thereafter, a function of performing control to erase data in the memory unit 206 is provided.
[0043]
Next, the operation of the semiconductor memory device 201 of the second embodiment will be described.
FIG. 11 is an explanatory diagram of file deletion processing.
As an example, a case where the file 1 is deleted will be described.
First, the host checks the file name identification unit 93 of the directory storage unit 209 to check whether or not the file 1 is stored. In this case, since it is stored, the valid information unit 91 and the stored information identification unit 92 are checked to confirm that this information is a valid file, and the data of the valid information unit 91 indicating the corresponding valid / invalid is invalidated. ("1" → "0").
[0044]
Next, the pointer 94 is checked to confirm the position of the file on the FAT storage unit 208 (in this case, 002H). Then, linking is performed based on the information of the pointer 81 on the FAT storage unit 208. In this case, since the link information is 002H → 003H → 008H, the link information to the data part on the FAT storage unit 208 is rewritten to 000H.
Next, this apparatus erases the data on the memory unit 206 corresponding to the link information (002H → 003H → 008H) on the FAT storage unit 208.
[0045]
As described above, in the second embodiment, when there is a file deletion request from the host, the corresponding pointer in the FAT storage unit 208 is set to 000H, and the corresponding area in the memory unit 206 is erased. For example, when writing to the corresponding area of the memory unit 206 next time, the writing process can be performed as it is, and the performance of the semiconductor memory device can be improved.
[0046]
Next, a semiconductor memory device in which data in the memory section is periodically erased in the second embodiment will be described as a third embodiment.
Example 3
FIG. 12 is a block diagram illustrating the configuration of the semiconductor memory device 301 according to the third embodiment. In the figure, the configurations of the host interface unit 303 to the directory storage unit 309 are the same as those of the host interface unit 203 to the directory storage unit 209 in the second embodiment, and a description thereof will be omitted here. The erasure position storage unit 311 stores position information of data to be erased from the memory unit 306.
[0047]
FIG. 13 shows details of the erase position storage unit 311.
The erase position storage unit 311 includes a read pointer 311a, a write pointer 311b, and a FAT address storage unit 311c.
The read pointer 311a is a pointer for reading data from the FAT address storage unit 311c, and the write pointer 311b is a write pointer for writing data to the FAT address storage unit 311c. The initial value thereof is “2”. is there. The FAT address storage unit 311c is a part that stores the address of the FAT storage unit 308 corresponding to the area of the memory unit 306 to be erased, and the area has an arbitrary size.
[0048]
Next, the erase processing operation of the third embodiment will be described.
FIG. 14 is a flowchart thereof.
This flowchart shows a process for deleting a file, in which the position to be deleted is stored in the deletion position storage unit 311 and the corresponding area in the memory unit 306 is deleted when the number of stored data exceeds a certain threshold. It is.
[0049]
First, the write pointer 311b is read (step S1), and the address of the FAT storage unit 308 corresponding to the area of the memory unit 306 to be deleted is stored in the FAT address storage unit 311c (step S2).
Next, the write pointer 311b is updated (step S3), and when it overflows, the write pointer 311b is initialized (steps S4 and S5). Further, the difference between the write pointer 311b and the read pointer 311a is obtained (step S6). If a certain threshold value is exceeded, that is, a threshold value with a certain number of data stored in the FAT address storage unit 311c is obtained. If it exceeds (step S7), the process proceeds to the next step S8. If the threshold is not exceeded, the process is terminated.
[0050]
If a certain threshold value is exceeded in step S7, the read pointer is read (step S8), and the address of the FAT storage unit 308 corresponding to the area of the memory unit 306 to be deleted is read from the FAT address storage unit 311c. Read (step S9).
Next, the corresponding area of the memory unit 306 obtained from the FAT address storage unit 311c is erased (step S10). Then, the read pointer 311a is updated (step S11), and when it overflows, the read pointer 311a is initialized (steps S12 and S13).
Then, it is checked whether or not the write pointer 311b matches the read pointer 311a, that is, whether valid data is stored in the FAT address storage unit 311c (step S14). In step S14, if they do not match (valid data is still stored), the process returns to step S8, and if they match (no valid data), the process ends.
[0051]
As described above, the semiconductor memory device 301 of the third embodiment is erased when the number of areas to be erased on the corresponding memory unit 306 exceeds a certain threshold in the semiconductor memory device 201 of the second embodiment. In addition to the effect of the second embodiment, the erasure process of the memory unit 306 can be performed in a concentrated manner. Therefore, even when the access to the apparatus is concentrated, the erasure process of the memory unit 306 is performed. Performance degradation due to can be minimized.
[0052]
Next, a semiconductor memory device in which the entire area of the memory unit is erased when a logical format is requested will be described as a fourth embodiment.
Example 4
FIG. 15 is a block diagram illustrating the configuration of the semiconductor memory device according to the fourth embodiment.
In the figure, the configuration of the host interface unit 403 to directory storage unit 409 is the same as that of the host interface unit to directory storage unit in each of the embodiments described above, and a description thereof will be omitted.
The processor unit 404 includes a format control unit 404a. The format control unit 404a has a function of only erasing the memory unit 406 without writing a specific pattern to the memory unit 406 when receiving a logical format request from the host which is the device. It is what.
[0053]
Next, the operation of the semiconductor memory device 401 having the above configuration will be described.
FIG. 16 is an explanatory diagram of logical format processing.
When the host instructs the logical format, the apparatus accepts a reset (000H) instruction for all information in the directory storage unit 409 and the FAT storage unit 408. When the processor unit 404 detects this instruction, the format control unit 404a Take control.
That is, all the pointers 94 in the directory storage unit 409 are set to “0”, and all the pointers 81 in the FAT storage unit 408 are set to “000H”. Then, when an instruction to write a specific data pattern is received in the entire area of the memory unit 406, the format control unit 404a does not write the specific data pattern and only erases the entire area of the memory unit 406. Do.
[0054]
As described above, in the fourth embodiment, when a logical format request is received, an operation of writing a specific data pattern to all areas of the memory unit 406 is not performed. Therefore, a write request to the memory unit 406 is not performed. Even if the data is received, it is not necessary to perform the erasing process once, and the data can be written as it is.
Therefore, the performance of the apparatus in such a case can be improved.
[0055]
Next, Example 5 will be described.
Example 5
FIG. 17 is a block diagram illustrating the configuration of the semiconductor memory device according to the fifth embodiment.
In the figure, the configuration of the host interface unit 503 to the directory storage unit 509 is the same as that of the host interface unit to the directory storage unit in each of the embodiments described above. The processor unit 504 includes a write control unit 504a. When it becomes necessary to perform overwriting (data rewriting) of the memory unit 506, the writing control unit 504a writes the overwriting data in the data non-storage area of the memory unit 506, and the FAT storage unit 508 and the directory storage unit 509 The pointers 81 and 94 have a function of rewriting to the address where data is newly written, and then erasing the already written area.
[0056]
Next, the operation of the semiconductor memory device 501 having the above configuration will be described.
FIG. 18 is an explanatory diagram of the data writing process.
Here, as an example, the data writing process of the file 2 (data capacity is equivalent to two clusters) will be described.
First, the host checks the file name identification unit 93 of the directory storage unit 509 to check whether the file 2 is stored. In this case, since it is stored, the valid information section 91 and the stored information identification section 92 are checked next to confirm that this information is valid data.
[0057]
Next, the pointer 94 is checked to confirm the position of the valid data on the FAT storage unit 508 (in this case, 004H). Then, linking is performed based on the information of the pointer 81 on the FAT storage unit 508. In this case, since the link information is 004H → 005H, this apparatus can determine that an overwriting process on the memory unit 506 is necessary. Therefore, this apparatus detects an unwritten area on the memory unit 506 and writes the corresponding information to the pointer 81 in the FAT storage unit 508 (in this case, “00CH” is written to 00BH and “FFFH” is written to 00CH). ).
Then, the corresponding pointer 94 of the directory storage unit 509 is rewritten (in this case, 004H → 00BH), the files 2- (1) and 2- (2) are written to the corresponding memory unit 506, and finally the FAT storage unit Data on the memory unit 506 corresponding to the link information (004H → 005H) on 508 is deleted.
[0058]
As described above, according to the fifth embodiment, when an overwrite request is received for the data in the memory unit 506, the overwrite data is written in the data non-storage area of the memory unit 506, and the FAT storage unit 508 and the directory are stored. Since the area where the overwrite request data is stored is erased after the pointer of the section 509 is rewritten, the data write process can be performed first even in the case of the overwrite request. By taking measures such as sending a write end response, it is possible to improve the performance during data rewriting.
[0059]
Next, a semiconductor memory device in which data in the memory section is periodically erased in the fifth embodiment will be described as a sixth embodiment.
Example 6
FIG. 19 is a block diagram illustrating a configuration of the semiconductor memory device according to the sixth embodiment.
In the figure, the configurations of the host interface unit 603 to the directory storage unit 609 are the same as those of the host interface unit to the directory storage unit in each of the embodiments described above. The erase position storage unit 611 is a storage unit for storing the address of data to be erased in the memory unit 606, which will be described later.
[0060]
The processor unit 604 includes a write control unit 604a and an erase control unit 604b. When the write control unit 604a receives an overwrite request for arbitrary data stored in the memory unit 606, the write control unit 604a writes the overwrite data in the data non-storage area of the memory unit 606, and the FAT storage unit 608 and the directory A function of rewriting the pointers 81 and 94 of the storage unit 609 to an address at which data is newly written is provided.
The erasure management unit 604b has a function of erasing data stored in an erasure position storage unit 611, which will be described later, when the memory unit 606 has not been accessed for a certain period of time, which will be described in detail later.
[0061]
FIG. 20 shows details of the erase position storage unit 611.
The erasure position storage unit 611 includes an empty flag 611a, a read pointer 611b, a write pointer 611c, and a FAT address storage unit 611d.
The empty flag 611a indicates whether or not valid data is stored in the FAT address storage unit 611d. The set state = no valid data in the FAT address storage unit 611d and the reset state = valid data in the FAT address storage unit 611d. Indicates presence. The initial value is “set state”.
The read pointer 611b is a read pointer for reading data from the FAT address storage unit 611d, and its initial value is “3”. The write pointer 611c is a write pointer for writing data to the FAT address storage unit 611d, and its initial value is “3”.
The FAT address storage unit 611d is a part that stores the address of the FAT storage unit 608 corresponding to the area of the memory unit 606 to be erased, and the area has an arbitrary size.
[0062]
Next, the operation of the semiconductor memory device 601 having the above configuration will be described.
FIG. 21 is a flowchart of the operation.
This flowchart shows a process of storing a position to be deleted in the erasure position storage unit 611 ((a) in the figure) and periodically erasing the deletion process of the written area when rewriting on the memory unit 606 is performed. This shows the process {(b)} in the figure for erasing the corresponding area in the memory unit 606 according to the data stored in the position storage unit 611.
[0063]
Here, “periodic” occurs after a certain period of time after the apparatus receives an arbitrary command from the host. If another command is received within a certain time after the command is received, it occurs after a certain time from the reception of a new command. That is, when the memory unit 606 is not accessed for a predetermined time, the corresponding area of the memory unit 606 is erased.
[0064]
First, the process of storing the position to be deleted in the erasure position storage unit 611 {(a)} in the figure will be described.
First, the empty flag 611a is reset (step S11), the write pointer 611c is read (step S12), and the address of the FAT storage unit 608 corresponding to the area of the memory unit 606 to be deleted is stored in the FAT address storage unit 611d. (Step S13). Next, the write pointer 611c is updated (step S14), and when it overflows, the write pointer 611c is initialized (steps S15 and S16).
[0065]
Next, a process {period (b)} in FIG. 5 that periodically erases the corresponding area of the memory unit 606 according to the data stored in the erase position storage unit 611 will be described.
First, it is checked whether or not the empty flag 611a is set (step S21). That is, it is checked whether valid data is stored in the FAT address storage unit 611d.
In step S21, the set state (no valid data) ends, and the reset state (valid data exists), the read pointer 611b is read (step S22) and corresponds to the area of the memory unit 606 to be deleted. The address of the FAT storage unit 68 to be read is read from the FAT address storage unit 611d (step S23).
[0066]
Next, the area of the corresponding memory unit 606 obtained from the address of the FAT address storage unit 611d is erased (step S24). Thereafter, the read pointer 611b is updated (step S25), and when it overflows, the read pointer 611b is initialized (steps S26 and S27).
Next, it is checked whether or not the write pointer 611c and the read pointer 611b match (that is, whether or not valid data is still stored in the FAT address storage unit 611d) (step S28). If yes (if valid data is still stored), end. On the other hand, if they match (when valid data is not stored), the empty flag 611a is reset (step S29), and the process ends.
[0067]
As described above, according to the sixth embodiment, as in the fifth embodiment, when an overwrite request is received for the data in the memory unit 606, the overwrite data is written in the data non-storage area of the memory unit 606. Since the pointers in the FAT storage unit 608 and the directory storage unit 609 are rewritten and the memory unit 606 is not accessed for a certain period of time, the corresponding area in the memory unit 606 is erased. In addition, the erasure process of the memory unit 606 is performed when no other process is performed. Therefore, even when data rewrite requests to the apparatus are concentrated, the process can be performed quickly. The performance can be improved.
[0068]
In the sixth embodiment, the configuration in which the corresponding area of the memory unit 606 is periodically erased is configured to be erased when the memory unit 606 has not been accessed for a certain period of time. Is set to a certain period, and when a process queue is provided and another process is performed at the timing of the erase process, the erase process is added to the queue, and each process including the erase process is performed according to this queue. You may comprise so that a process may be performed.
[0069]
In the sixth embodiment, as in the third embodiment, the erasing process may be performed when the number of data stored in the FAT address storage unit 611d exceeds a certain threshold value.
Further, on the contrary, in the third embodiment, similarly to the sixth embodiment, the erasure processing of the corresponding area in the memory unit 306 is executed when the memory unit 306 is not accessed for a certain period of time. Also good.
[0070]
【The invention's effect】
As described above in detail, according to the semiconductor memory device of the first invention, when a write request to the subdirectory is received, information is not written on the memory unit but stored in the subdirectory storage unit. This eliminates the need for write access to the subdirectory on the memory unit, and can improve performance in such a case.
[0071]
According to the semiconductor memory device of the second invention, when the file deletion request is made, the directory storage unit and the file allocation table storage unit are controlled and then the corresponding area of the memory unit is erased. When writing to the corresponding area above, no erasing process is required, and the performance of the apparatus can be improved.
Further, according to the semiconductor memory device of the third invention, in the semiconductor memory device of the second invention, the area to be erased on the memory portion is configured to be performed when the number exceeds a certain threshold value. In addition to the effect of the second invention, since the erasing process can be performed in a concentrated manner, even when the access to the apparatus is concentrated, the performance degradation due to the erasing process of the memory section can be minimized.
[0072]
According to the semiconductor memory device of the fourth aspect of the present invention, when the logical format request is received, the entire area on the memory unit is erased, so that an erasing process is not required when data is newly written to the memory unit. Thus, the performance of the apparatus can be improved.
[0073]
According to the semiconductor memory device of the fifth aspect of the present invention, when the area on the memory unit is overwritten, the overwritten data is written to the unwritten area of the memory unit, and then the area requested to be overwritten is erased. Therefore, even in the case of an overwrite request, the data writing process can be performed first, so that the performance in such a case can be improved.
Further, according to the semiconductor memory device of the sixth invention, in the semiconductor memory device of the fifth invention, since the corresponding area on the memory unit is erased when there is no access to the memory unit for a certain period of time, Even when data rewrite requests to the apparatus are concentrated, processing can be performed promptly, and performance in such a case can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of a semiconductor memory device according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a comparative example of a semiconductor memory device.
FIG. 3 is a detailed explanatory diagram of each part in a semiconductor memory device of a comparative example.
4 is a detailed explanatory diagram of a subdirectory in FIG. 3. FIG.
FIG. 5 is an explanatory diagram of file erasing processing in a semiconductor memory device of a comparative example.
6 is a detailed explanatory diagram of a subdirectory in FIG. 5. FIG.
FIG. 7 is an explanatory diagram of logical format processing in a semiconductor memory device of a comparative example.
FIG. 8 is a diagram for explaining the operation of the semiconductor memory device according to the first embodiment of the present invention.
FIG. 9 is a detailed explanatory diagram of a subdirectory storage unit in the first embodiment of the semiconductor memory device of the present invention;
FIG. 10 is a block diagram showing a configuration of a semiconductor memory device according to a second embodiment of the present invention.
FIG. 11 is an explanatory diagram of file erasing processing in the second embodiment of the semiconductor memory device of the present invention.
FIG. 12 is a block diagram showing a configuration of a semiconductor memory device according to a third embodiment of the present invention.
FIG. 13 is a detailed explanatory diagram of an erasing position storage section in the third embodiment of the semiconductor memory device of the present invention.
FIG. 14 is a flowchart of an erasing process in Embodiment 3 of the semiconductor memory device of the present invention.
FIG. 15 is a block diagram showing a configuration of a semiconductor memory device according to a fourth embodiment of the present invention.
FIG. 16 is an explanatory diagram of logical format processing in Embodiment 4 of the semiconductor memory device of the present invention.
FIG. 17 is a block diagram showing a configuration of a semiconductor memory device according to a fifth embodiment of the present invention.
FIG. 18 is an explanatory diagram of data write processing in the fifth embodiment of the semiconductor memory device of the present invention.
FIG. 19 is a block diagram showing a configuration of a semiconductor memory device according to a sixth embodiment of the present invention.
FIG. 20 is a detailed explanatory diagram of an erasing position storage unit in a sixth embodiment of the semiconductor memory device of the invention.
FIG. 21 is an operation flowchart of embodiment 6 of the semiconductor memory device of the invention.
[Explanation of symbols]
101, 201, 301, 401, 501, 601 Semiconductor memory device
106, 206, 306, 406, 506, 606 Memory part
108, 208, 308, 408, 508, 608 File allocation table (FAT) storage
109, 209, 309, 409, 509, 609 Directory storage
111 Subdirectory storage
204a, 304a Memory erase control unit
311 and 611 Erase position storage unit
404a Format control unit
504a, 604a Write control unit
604b Deletion management unit

Claims (2)

A memory unit composed of flash memory;
A directory storage unit having valid information indicating whether the data stored in the memory unit is valid or invalid, and a pointer corresponding to the data;
A file allocation table storage unit indicating a data address of the memory unit corresponding to the pointer of the directory storage unit;
When an erasure request is received for any data in the memory unit, the valid information corresponding to the data in the directory storage unit is invalidated and the pointer of the data in the file allocation table storage unit is reset. A semiconductor memory device comprising: a memory erasure control unit that rewrites an address in a state and erases the data in the memory unit. The semiconductor memory device according to claim 1 .
An erasure position storage section for storing position information of data to be erased in the memory section as position information of an erasure unit of the data;
When the number of erasure units of data stored in the erasure position storage unit exceeds a preset threshold value, based on the position information of the data stored in the erasure position storage unit, the memory unit And a memory erasure control unit for erasing data to be erased.

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