JPH0695955A - Flash file system - Google Patents

Abstract

PURPOSE:To attain high speed processing by collecting discontinuous and unused areas by a random access operation and reconstituting a file system so that the system is not used by other valid data. CONSTITUTION:An area is updated by an instruction outputted from an insertion/extraction mounting part 11 or a reset signal outputted from the system. Updating processing is executed by a positional information managing part 13 based upon the instruction. The managing part 13 reads out the positional information of each record from a flash memory part 4 in a memory card l, changes the constitution of the information and then stores the changed contents in a positional information storing area 14. As a matter of course, the flashing of all erasing blocks should cause the updating of the area 14. Namely an initializing request is inputted to a flash processing part 12, which executes flash processing and the processed contents are inputted to the managing part 13 to update the area 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can suppress performance deterioration, disperse data without concentrating writing on a fixed area, and maintain the interface of a conventional FAT file system. Flash file system that can be.

[0002]

2. Description of the Related Art Conventionally, there are a mask ROM in which contents are written at the time of manufacturing and a PROM (Programmable ROM) in which a user applies electricity to write a program.
Erasable and programmable PROMs that can be erased and rewritten by a light emitting device etc.
ROM). Of the rewritable read-only memory PROMs, flash memory that erases all contents at once by applying electricity (flash PRO
M) has a simple memory structure and a small chip,
Since it is cheaper than a DRAM, it has recently attracted attention.
By the way, flash memory has two features,
They impose special requirements on the file system that controls the device. One is that it is always possible to have a bit value of 1 be 0, whereas a bit value of 0 is 1
(That is, erasing bit values) requires complicated processing that is not a bit boundary operation. in this way,
In flash memory, erasing must be done in device units, and even with recent technologies, rewriting is impossible unless at least 32 Kbytes are erased. The other one is that a certain time is required for erasing.

The flash memory is a conventional FA.
T file system (fixed length sector access method)
Unlike file, I / O operation is trapped (preemption)
Then, the directory and the data are stored in a variable length record, and the pointers are chained from the lower memory to the upper memory and stored. The trap method is the same as the method (redirector method) performed by a shared drive on the network, and physical access for read / write in sector units is not permitted. In addition, as a method of storing information, a pointer chain method that uses a physical address instead of a sector number is used to extend to a higher address so that a stack is used. As described above, there are the following four reasons why the flash file system has recently received attention. (A) It can be made smaller and lighter than the conventional magnetic media system, and (b) it is more portable than the conventional magnetic media system because it is more shock resistant. (C) A power supply for backing up the contents is unnecessary as compared with the conventional SRAM system. (D) As compared with the conventional EEPROM system, the device can be downsized, so that the capacity can be increased. The flash file system is described in, for example, the functional specification (Revision 0.01) of Intel Corporation / Microsoft Corporation (1990-02-05).

[0004]

However, as described above, the flash file system has the following problems. Although it is easy to set the bit value 1 to 0, when setting 0 to 1, it is necessary to flush (set all bit values in the block to 1) in units of erase blocks (about 32 Kbytes). The flash consumes a certain time (about 1 second). Like magnetic media, infinite writing / rewriting is impossible (about 100,000 times). Furthermore, as another problem, there are the following three points. Unlike conventional file systems, file input / output instructions are trapped like network drives, and data is saved to use the stack, so read / write in sector units is not possible. Yes, some applications (eg, CHKDSK, not-utility, etc.) cannot be used. When saving data, it is done by chaining with pointers like a stack, so it is necessary to reconstruct the entire file system in order to erase unnecessary data records. . As a result, an external memory is required to store the previous data. If only one byte in the file is updated, the file data after the modified byte must be rewritten to another area. An object of the present invention is to solve these conventional problems and to eliminate the restrictions on (a) applications.
Maintain the AT file system interface,
(B) In order to suppress performance deterioration as much as possible, useless rewriting and the number of flashes are reduced, and (c) data is distributed so that writing to a fixed area is not concentrated, (d)
It is to provide a flash file system that does not use external memory for flash operations.

[0005]

To achieve the above object, the flash file system of the present invention comprises:
(B) In a flash file system composed of a flash ROM and having a plurality of erase blocks, a plurality of records, and whether each record is unused or invalid, and used When it is in the middle, it comprises a plurality of erase blocks each of which is composed of position information indicating a sector number and a record number, and each record exists randomly and independently of other records. One of the blocks is characterized by gathering non-contiguous unused areas by the action of random access so that it will not be used by other valid data for Garbage Collection to rebuild the file system. I am trying. The position information associating the (b) record with the logical file system existence position is inserted between the records of the flash ROM and the position on the RAM of the system side connected to the flash ROM. It is also characterized in that when the system side reads the specified record of the flash ROM by reading the information into the information storage area, the location information storage area on the RAM is referred to. Further, (c) when updating the record of the flash ROM from the system side, when the configuration bit in the record does not change from 0 to 1 between the previous data and the update data. It is also characterized by overwriting on the same record.

[0006]

In the present invention, it is not necessary to have an external buffer for storing the original data of the flash ROM.
Even when 0 is rewritten to 1, it is only necessary to process and write the original data and then perform the flash process. Conventionally, since the original data was read into the buffer, and after the flash processing, the original data was processed and written, the processing was slow, but in the present invention, each record is independent. However, high speed processing is possible.
Further, in the conventional flash ROM, the pointers are chained and stored from the lower order to the upper order, but in the present invention, each record is not chained and exists independently.
Since the bage block is also floating, that is, it is not a fixed block but a variable block, the writing is not concentrated in the fixed area and the data is dispersed. Further, since the buffer is unnecessary, it can be effectively used and can be released to other applications. Furthermore, in the present invention, data is only overwritten except when changing from 0 to 1, and as a result, the number of unnecessary rewritings and flashes is reduced, so that there is almost no deterioration in performance. Further, in the present invention, since it corresponds to the conventional FAT file system, physical access is possible, and there is no restriction such as application. Further, as with the conventional flash ROM, a backup power supply is unnecessary.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a perspective view of a flash file system showing an embodiment of the present invention. Here, the case of handling a flash memory card is shown, but the same applies to other flash memories. In Figure 1,
Memory card 1 composed of flash ROM 4
Shows a system unit 3 mounted as a file system via the memory card slot 2.
FIG. 2 is a block diagram of the data in the flash ROM in FIG. As shown in FIG. 2, a 1M-byte flash ROM has erase blocks # 0 to # 31 (each of which is an erase block).
32K bytes). The contents of each erase block are the records # 0 to # 2 starting from 8-byte control information.
51 pieces of data (each 2 + 128 bytes) are arranged, and the position information (each 2 bytes) of the record #n is inserted between the pieces of data. These position information are the sector numbers of 1 to 16383 (of which 1638
3 is an unused record) and the sector record number (0 to 0)
3). The length of the position information, that is, the sector length is 2 bytes × 256 = 51 in one erase block.
It is 2 bytes. Therefore, in response to a read / write request in sector units from the system side, 4 records / sectors can be accessed. In this case, the access target is 32 erase blocks, 1 erase block per erase block. The number of records = 252 and the total number of sectors = 1953. Note that these numerical values are examples and the number of Garbage blocks is also set to 1 here.

Next, the definitions of terms will be described. Garba
The ge blocks are some of the erase blocks, and are 1 in FIG. That is, when there are no unused records and there are invalid records,
Used to make an invalid record an unused record (Garbage Collection). A record is a data storage unit in the flash ROM. Here, the sector size (512 bytes) is longer than the in-record data area size (2 + 128 bytes). Gar
The bage collection is to collect unused areas that are discontinuous by the action of random access and rebuild the file system. The position information indicates the number of the sector and the number of the record if each record is unused, invalid, or in use. The control information is a buffer area for preventing the record from extending over the erase block. Then, information on whether or not the erased block is a garbage block, the number and size of records contained in the block, and the size of control information are stored. Here, in the case of the Garbage block, all bits are set to 1, and other information is contained. The location information storage area is a memory area in the system for storing location information. It is used to quickly point the area of interest. As in this embodiment, the data record is random and independent of other records (that is,
Since there is no pointer chain, etc.), it is indispensable for record retrieval. Based on the in-record position information (position information of record #n), information on what number record of which erase block is arranged is arranged in the order of sector numbers.

FIG. 3 is a block diagram of the file system in FIG. In FIG. 3, 1 is a memory card and 4 is
Is a flash memory unit which is a component of the memory card 1, 5 is a connector for connecting the system and the memory card 1, 11 is an insertion / extraction monitoring unit for monitoring the insertion or removal of the connector 5, and 12 is a flash memory unit. 4, a flash processing unit that performs the flash process, 13 a position information management unit that manages the position information, 14 a position information storage area that stores the position information, 15 a write processing unit that writes according to the write request, and 16 a read request Reference numeral 17 denotes a reading processing unit for reading data according to the above, and 17 is a system memory unit in the system. FIG. 4 is a configuration diagram of the position information storage area in FIG. Based on the record #n position information,
By arranging in the order of sector numbers and in the order of intra-sector record numbers of the same sector number, the corresponding record can be pointed at high speed. In one location information storage area, erase block numbers 0-254 and 0-254
A record number in the erase block of 255 (of which 255 is an unwritten record) is stored, and is composed of 2 bytes in total. FIG. 5 is a flowchart of the updating operation of the location information storage area. Here, b is the erase block number, rb is the erase block record number, s is the sector number, and rs is the sector record number. In this embodiment, since a removable (insertable / unpluggable) file system is considered, updating of this area is instructed by the plugging / unplugging monitoring section 11 or a system reset signal (power on / off, reset switch). Or caused by the initialization process). The update by these instructions can be performed before the read / write processing by holding the exchange in the status flag. The update process is executed by the position information management unit 13 based on the above instruction. Location information management unit 13
Reads the position information of each record from the flash memory unit 4 in the memory card 1 and stores the position information in the position information storage area 1
Change the configuration to 4 and save. At this time, the area corresponding to the unwritten sector is FFFFh (all bits are 1). In FIG. 5, first, all the position information storage areas are set to FFFFh by the reset signal (step 101). The position information (s, rs) indicated by (b, rb) is read (step 104), s
= 1 to 16382, it is determined whether or not the record is a valid record (step 105), and (b, rb) is stored in the position information storage area indicated by (s, rs) (step 106). If it is saved, the process is undone. Then, every time the erase block number b is changed to 0 to 31,
The same operation (104 to 106) is repeatedly executed (step 102). Record number rb in erase block is 0
Every time it is changed to 251, the same operation is repeated (104 to 1
06) is executed (step 103).

Next, the initialization (FORMAT) of the flash file system will be described. When operating a file system on an operating system (OS), some kind of initialization processing is usually required. This initialization process includes a physical format (work for partitioning the inside of the medium) and a logical format (work for writing information required by the OS, for example, directory FAT).
It is composed of two types. In this embodiment, since the physical format maintains the flash of all erase blocks and the logical format maintains the compatibility with the conventional magnetic media, it corresponds to a normal operation. The normal work depends on the OS, but here, it is based on the FAT file system of MS-DOS. In the case of this embodiment, the physical format (flushing work) does not need to write a specific ID (partition information or position information), so all erase blocks need only be flushed. That is, the position information is updated by the writing process, and by flashing, it automatically becomes an unused record. In addition, the logical
The matting can be performed in the same manner as the writing process. The flushing of all erase blocks must, of course, cause an update of the location information storage area. That is, in this case, in FIG. 3, an initialization request is input to the flash processing unit 12, the flash processing is performed in the flash processing unit 12, and then is input to the position information management unit 13 to store the position information storage area. Updates are made.

FIG. 6 is a flowchart of the reading process according to the present invention. A read request from the system side (usually the OS) is made in sector units. In this embodiment, the sector is divided into several records, and each record is stored in a non-contiguous area. Here, for the sake of convenience of explanation, the capacity occupied by the position information and the number determined by the trade-off of rewriting occurrence frequency are divided into four. Therefore, in FIG. 3, when a read request is generated (the sector number (s) and the transfer address to the system memory unit 17 are input), the read processing unit 16
Accesses the position information storage area 14 to determine where in the flash memory section 4 the data of the designated sector is stored. Then, from the location information storage area 14 is represented by (s, rs) (b, rb)
Is acquired (step 112). This information is FFFFh
When the erase block number field is 255 (step 113), it is determined that the sector has not been written, and the dummy data of all 0 is transferred to the designated address of the system memory unit 17. (Step 11
5). Further, when this information is instructing a record having the information (step 113), the data in the record is inverted and transferred to the designated address of the system memory unit 17 (step 114). ). When inverting the data, in order to avoid the change from bit 0 to 1 as much as possible, all bits are set to 1 immediately after initialization, and thereafter,
The state of 1 is preferably kept until the valid data is written. Therefore, if all 1's are written, it appears to the system side that 0 is written. That is, in the FAT file system, unused areas of directories and FATs are represented by 0.

FIG. 7 is a flowchart of the writing process according to the present invention. In this case, a write request from the system side is made in sector units, as in the read process, and in this embodiment, it is divided into records and stored in non-contiguous areas. When a write request occurs,
The write processing unit 15 refers to the position information storage area 14 and determines whether or not the sector has already been written (steps 122 and 123). If it has been written, it is compared with the data to be updated (specified data) (step 124) and it is judged whether or not the change from 0 to 1 occurs (step 125). ), If it does not occur, the data is overwritten. That is, the designated write data is inverted and transferred to the record represented by (b, rb) (step 133). On the other hand, when the change from 0 to 1 occurs, the previous record is invalidated (step 126). That is, the in-record position information is set to 0, the corresponding position in the position information storage area is set to FFFFh (not written), and an unused record is acquired (step 127). If it can be obtained (step 128),
The record is validated (step 132). That is, the position information in the record is set to the designated sector number / record number, and the block number and the record number of the record are set to the corresponding positions in the position information storage area. Then, like the reading process, the designated write data is inverted and transferred to the record represented by (b, rb) (step 133).

In FIG. 7, it is judged whether or not it has already been written, that is, whether b = 0 to 254 (step 123), and if it has not been written, the unused record is similarly used. A record is acquired (unused records other than the Garbage block) (step 127), the record is validated (step 132), and the data is transferred (step 133). When obtaining an unused record, search is performed excluding the Garbage block (step 12).
7). That is, blocks in which the control information is all 1s are excluded. However, when there are no unused records (step 128), information (including control information) other than the invalid record of the erase block including the invalid record (position information in the record is 0000h) is also included. The data is transferred to the Garbage block (step 129) and a flash request for the original block is requested to the flash processing unit 12 (step 131). In that case, the invalid record automatically becomes an unused record. When the flush ends, the block automatically becomes a Garbage block. At this time, the block number of the corresponding record in the position information storage area 14 is updated to a new value (step 130).

As described above, in the present embodiment, (a) it is not necessary to prepare a buffer for storing the original data in the case of Garbage Collection on the system side. Can be used effectively and can be released to other applications. (B) G
The part that was an arbage block becomes a data block, and vice versa. It operates as if it is used both as a garbage block and a data block, so the original data is saved externally. Compared to the case where a buffer is provided,
The amount of data transferred can be reduced. That is,
In the latter case, the original data is read->flash-> the original data is processed and processed in the order of writing. In the present embodiment, the original data is processed and then written-> flash. Can be processed by. (C) Garbage block is floating,
Since it is not a fixed block but a variable block,
There is no concentration of writing in the fixed area. (D) Conventional F
Since it is compatible with the AT file system, physical access is possible, and restrictions such as applications are eliminated. (E) A file system that does not require a backup power supply can be realized. (F) It is a set of blocks that are not chained, and even though each record exists independently, the position where each record exists can be grasped at high speed.
(G) Since the correspondence between sectors and records is simple,
It is possible to deal flexibly with changes in record size. (H) 0
Since the data is overwritten except when the change from 1 to 1, the number of unnecessary rewritings and the number of flashes can be reduced.

[0015]

As described above, according to the present invention, the conventional F
Since the interface of the AT file system can be maintained and the number of flashes and unnecessary rewriting are eliminated, it is possible to minimize performance deterioration.
Further, since the writing concentration on the fixed area is eliminated, the data can be dispersed, and since the external memory is not used for the flash operation, the memory on the system side can be effectively used. Further, the transfer amount of data is small, the change of the record size and the like can be dealt with flexibly, and the backup power source can be eliminated.

[0016]

[Brief description of drawings]

FIG. 1 is a flash file showing an embodiment of the present invention.
FIG. 3 is a perspective view of the system.

FIG. 2 is a configuration diagram of data in a flash ROM in FIG.

FIG. 3 is a configuration diagram of a file system in FIG.

FIG. 4 is a configuration diagram of a location information storage area in FIG.

FIG. 5 is an update flow chart of the location information storage area in the present invention.

FIG. 6 is a flowchart of reading processing according to the present invention.

FIG. 7 is a flowchart of a writing process according to the present invention.

[Explanation of symbols]

 1 memory card 2 memory card slot 3 system unit 4 flash ROM 5 connector 11 insertion / extraction monitoring unit 12 flash processing unit 13 position information management unit 14 position information storage area 15 write processing unit 16 read processing unit 17 system memory unit

Claims (3)

[Claims] 1. A flash file system comprising a flash ROM and comprising a plurality of erase blocks, wherein a plurality of records and whether each record is unused or invalid is set. , Again when in use,
Each record has a plurality of erase blocks which are composed of position information indicating a sector number and a record number, and each record exists randomly and independently of other records. One of the erase blocks is provided. For the Garbage Collection that rebuilds the file system by collecting discontinuous unused areas by the action of random access, another effective data
A flash file system characterized by being protected from use by a computer. 2. The flash file system according to claim 1, wherein position information associating the record with a logical file system existing position is inserted between respective records of the flash ROM. , The position information on the RAM, which is read into the position information storage area on the system side RAM connected to the flash ROM and is accessed from the system side to the designated record of the flash ROM. A flash file system characterized by being accessed by referring to a storage area. 3. The flash file system according to claim 2, wherein when a record of the flash ROM is updated from the system side, a configuration bit in the record has a previous data and an update data. -A flash file system characterized by overwriting on the same record when a change from 0 to 1 does not occur between data.