JP4888333B2 - Flash disk device - Google Patents

Description

  The present invention relates to a semiconductor disk device, and more particularly to a flash disk device using a flash memory.

  In recent years, with the increase in capacity and cost of non-volatile memories in recent years, flash disk devices, which are disks using non-volatile memories, have been developed, and many products are beginning to circulate in the market.

  A large-capacity nonvolatile memory element generally used in this flash disk device is an AND type / NAND type flash memory. However, a bit error occurs in data stored in the flash memory with a certain probability. In addition, erasing is generally performed in units called 16 KB blocks, but the number of times that erasure can be performed in the same block is limited to 100,000 to 1 million times.

  In general, a flash memory is composed of a plurality of blocks, and each of these blocks is composed of a plurality of pages. A page is a unit of reading (reading) / writing (writing), and is usually set to 512 bytes (bytes) having the same size as a sector which is a minimum unit of reading / writing in a hard disk device such as a magnetic disk device. Therefore, one block is composed of 32 pages.

  When rewriting data in each page, normally, new data is written after erasing previous data. As described above, a block is a unit to be erased, and even if rewriting is a partial page in this block, it is necessary to erase this entire block.

  By the way, since there are no free pages in the flash memory when writing is performed, in order to secure a certain amount of empty blocks, periodic garbage collection is performed and write pages in blocks with many unused pages. Is moved to another block to execute an unused block.

  Generally, garbage collection is executed under the control of the MPU when there is no access from the host machine for a certain period of time, or when the number of empty blocks in the flash memory becomes a predetermined number or less (see, for example, Patent Document 1). ).

  FIG. 9 shows an unused page list for managing unused pages in the conventional flash disk device. As shown in the figure, the unused page list searches the number of unused pages in order for all blocks of each chip, and stores the chip number, block number, and number of unused pages in a list. It was something to keep.

  For example, in the chip number A of the first chip, only block number 5 and block number 8 have unused pages, and 14 pages and 5 pages are unused, respectively.

In the conventional flash disk device, the above-described unused page list is used to move the write page in the block having many unused pages to another block to make it an unused block, that is, a garbage collection operation. It was.
JP 2005-242897 A

  However, in the conventional flash disk device, since unused pages are managed by the unused page list of FIG. 9 and the garbage collection operation is performed, when the write operation to the flash memory is performed and the number of empty blocks decreases, The frequency of garbage collection increases, frequently searching for blocks with many unused pages, and the garbage collection operation takes time. In the worst case, the garbage collection operation will not be in time before the next write operation, and the write There was a problem that the operation was affected.

The present invention employs the following means in order to solve the aforementioned problems. That is, in a flash disk device having a plurality of blocks that are write units composed of a plurality of pages, an unused page management table storing a corresponding block number for each number of unused pages is provided, and the unused page management table Was used to start garbage collection from blocks with a large number of unused pages.

  According to the flash disk device of the present invention, an unused page management table that can manage a corresponding block for each number of unused pages in the flash memory is provided, and blocks that have a large number of unused pages are provided by the unused page management table. Since the garbage collection process is performed, it is easy to search for a block having a large number of unused pages, and the garbage collection process time can be shortened.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element common to drawing.

(Constitution)
FIG. 1 is a diagram illustrating the configuration of the flash disk device according to the first embodiment, and FIG. 2 is a diagram illustrating the configuration of blocks and pages of the flash memory.

  As shown in FIG. 1, the flash disk device according to the first embodiment is connected to a host machine 1 by a host I / F bus 2 that is an interface (hereinafter referred to as “I / F”) with a host machine 1 such as a host CPU. It is connected.

  It has a microprocessor unit (hereinafter referred to as “MPU”) 11 that controls the entire apparatus. The MPU 11 includes a RAM 11a, a read-only memory (hereinafter referred to as “ROM”) 11b, and an input / output (hereinafter referred to as “I / O”). Port 11c and the like, and a non-volatile memory 12 is further connected.

  The nonvolatile memory 12 is controlled by the MPU 11 and is composed of a nonvolatile memory that can be rewritten in units of words in order to store information such as a block management table and an unused page management table, which will be described later.

  The flash disk device 10 is provided with a host I / F controller 13 for controlling the host I / F bus 2. The host I / F controller 13 processes the host I / F protocol and exchanges data with the host machine 1. A buffer memory 15 is connected to the host I / F controller 13 via the internal data bus 14. ing.

  The buffer memory 15 is a memory that temporarily stores and processes read / write data from the host machine 1. A flash memory controller 16 is connected to the internal data bus 14, and one or more flash memories 20 are connected to the flash memory controller 16 via a flash memory bus 17.

  The flash memory controller 16 controls access to the flash memory 20 in accordance with an instruction from the MPU 11, and includes a data reading unit 16a, a data writing unit 16b, a block erasing unit 16c, and the like. One or more flash memories 20 are memories that store write data from the host machine 1 in a nonvolatile manner.

  The flash memory 20 is composed of a plurality of blocks as erase units. In FIG. 2, the Nth block is shown as a block 21-N, and the N + 1th block is shown as a block 21- (N + 1). Each block 21 has a plurality of pages 22-0, 22-1,..., 22-31 which are read / write units. For example, if one page has a storage capacity of 512 bytes and one block is 16 KB, one block is composed of 32 pages.

  In the flash memory 20, even if a part of the pages 22 in the block 21 is rewritten, the rewriting is performed after the entire block 21 is erased.

  FIG. 4 shows the configuration of the flash memory according to the first embodiment of the present invention, and is a logical configuration diagram of the flash disk device 10 of FIG.

  In order to convert logical sector numbers 0, 1, 2,..., J as logical sector addresses 25 designated by the host machine 1 into page addresses that are physical addresses on the flash memory 20, Stores an address table 30. The address table 30 stores a plurality of address conversion data 31-0, 31-1, 31-2, ..., 31-K for converting a logical sector into a physical page.

  Further, in the nonvolatile memory 12, an unused page management table 32 for managing unused pages in the flash memory 20, and blocks 21-0, 21-1,..., 21-L in the flash memory 20 are stored. And a block management table 33 for managing the number of rewrites and the like. The plurality of blocks 21-0 to 21-L stored in the flash memory 20 have a plurality of pages 22-0, 22-1,.

  In the flash disk device of the first embodiment, an address table 30 is prepared in the non-volatile memory 12, and a mapping from a logical sector number, which is a sector address visible to the host machine 1, to a physical page number on the flash memory 20 is performed. Hold. A plurality of extra pages 22-i are prepared in the flash memory 20, and unused page information is registered and managed in an unused page management table 32 described later.

  This unused page management table 32 is a two-dimensional array composed of the number of unused pages and an index. 0xFFFFFFFF is recorded as initial data, and the corresponding chip number and block number are indexed for each number of unused pages. Recorded in order from 0. Therefore, the array without the corresponding chip number and block number remains recorded with the initial data 0xFFFFFFFF.

  As will be described later with reference to FIG. 5, the temporary storage page list 34 is stored in the RAM of the MPU 11 instead of in the flash memory, and the chip number and block number having an unused page while referring to the address table 30. The result of totaling the number of unused pages is temporarily stored.

(Operation)
With the above configuration, the flash disk device of the first embodiment operates as follows. Note that the read operation and the write operation are the same as those in the prior art, and thus the description thereof is omitted for the sake of brevity.

  The garbage collection operation is started when there is no access from the host machine 1 for a certain period of time or when the number of empty blocks in the flash memory falls below a certain amount. This operation will be described in detail below with reference to the configuration diagram of the unused page management table in FIG. 3, the configuration diagram of the temporary storage page list in FIG. 5, and the operation flowchart in FIG.

  When the garbage collection operation is started, first, a temporary storage page list 34 indicating the state of each page is created (step S1), and as shown in FIG. 5, temporary pages corresponding to pages 22 that are not used in the address table 30 are created. An unused flag is set in the storage page list 34 (step S2).

  Next, referring to the temporary storage page list 34, all unused pages are erased (step S3), all the flags of the corresponding page are erased, and unused pages in the unused page management table 32 of FIG. The erased chip number and block number are written in the index of 0xFFFFFFFF having a smaller index, assuming that all 32 rows in the block, that is, all the blocks are unused blocks (step S4). In the case of the state shown in FIG. 3, data is written to the index “3”.

  In step S4, in addition to the case where all the pages are not used, the temporary storage page list 34 is referred to for all chips and blocks having some unused pages. An unused page management table 32 is created. Also in this case, the index is written to the index of 0xFFFFFFFF having a smaller index.

  For example, in the example of the chip number C and block number k stored in the index 2 with 6 unused pages in FIG. 3, the unused page with the chip number C and block number k from the temporary storage page list in FIG. The number is counted, indicating that there are 6 unused pages.

  Then, it is determined whether the number of unused pages in the unused page management table 32 is 32, that is, whether the number of unused blocks is equal to or larger than a certain amount (step S5), and the total number of unused blocks is a certain amount. If there is more than one, the garbage collection operation is unnecessary, so this processing is ended as it is.

  On the other hand, if there are not more than a certain number of unused blocks, a garbage collection operation is required. Therefore, the number of unused pages other than the number of unused pages when all the blocks in the block are not used is 32. The block having a large number of unused pages is referred to (step S6), and all the valid data of the block having many unused pages, that is, the few used pages are read (step S7). An unused flag is set at the position (step S8).

  For example, in the example of the unused page management table 32 in FIG. 3, when all blocks in the block are unused (that is, the number of unused pages is 32) and a block with many unused pages is referenced, unused pages Since no block with unused pages is registered in the 31 rows, the 30 rows are referred to in order.

  Then, the chip number A and the block number a are registered in the index “0” of 8 unused pages (that is, the number of used pages is 32−8 = 24). Referring to the corresponding block of the temporary storage page list 34, it can be seen that 24 pages such as page 1 are used pages, so all the data of these pages are read out, and the chip number A and block number of the temporary page list 34 are read out. Set an unused flag on all pages of a.

  Next, the read data is referred to the unused page management table 32 to preferentially select a block with many unused pages and a large index, and the read data is written to the block (step S9). At this time, if the data capacity is large and cannot be written in one block, the data is divided and written in each block. Then, the correspondence between the logical sector number in the address table 30 and the physical page is updated as the page moves between blocks.

  For example, in the example of FIG. 3, when moving the number of unused pages, the data recorded in the chip number A and the block number a registered in the index “0”, the data to be moved is as described above. Since there are 24 pages, a block that can store them is extracted. In the case of this example, there is only a block that is free of 8 pages at the maximum, and there is no block in which all 24 pages can be written. Therefore, the chip number A of index 3 and 8 in block number d, chip number A of index 2 and block Eight in the number c, eight in the chip number A in the index 1, and eight in the block number b are transferred, and the correspondence between the logical sector number and the physical page in the address table 30 is updated as the block moves (step S10).

  Then, returning to the above-described step S3, the unused block generated by the data movement from step S6 to step S9 is erased, and the erased chip number and block number are used as the number of unused pages in the unused page management table 32 of FIG. Is written as an unused block in the entire block, and its chip number and block number are written in the index of 0xFFFFFFFF having a smaller index. Then, the unused page management table 32 of FIG. 3 is created for each unused page by referring to the temporary storage page list 34 even for a block having some unused pages.

  For example, in the case of the example of FIG. 3, since the block of chip number A and block number a of index 0 is not used due to the above-described data movement, the number of unused pages is 32 in index 3, and chip number A and block The content of the index 0 in which the number a is recorded and the number of unused pages is 8 is 0xFFFFFFFF.

  Since the index 1 having 8 unused pages is also written to the 8 unused pages with the chip number A and the block number b, there is no unused page, and the content of the index 1 is 0xFFFFFFFF It becomes. Similarly, the contents of index 2 and index 3 are also 0xFFFFFFFF.

  Then, the number of newly generated unused blocks is checked again. If a predetermined number of unused blocks can be secured, this process is terminated. If the predetermined number cannot be secured, steps S6 to S10 and S3 are performed. The operation of S5 is repeated.

(Effect of Example 1)
As described above, according to the flash disk device of the first embodiment, an unused page management table capable of managing a corresponding block for each number of unused pages is provided, and the number of unused pages is determined by the unused page management table. Since the garbage collection process is performed from a large number of blocks, it is easy to extract a block having a large number of unused pages, and the processing time can be shortened.

(Constitution)
The flash disk device according to the second embodiment performs garbage collection every predetermined number of blocks, for example, 200 blocks (3.2 MB), and starts garbage collection in the nonvolatile memory 12 as shown in FIG. A garbage collection start position storage unit 40 for storing the chip number and block number to be stored is provided.

  Then, when the garbage collection for the predetermined number of blocks is completed, the start chip number and the block number position are updated and stored in the garbage collection start position storage unit 40, and the garbage collection starts at the next garbage collection. The garbage collection can be performed from the chip number X and the block number Y stored in the position storage unit 40.

  Other configurations are the same as the configurations of the first embodiment, and detailed description thereof is omitted for the sake of brevity.

(Operation)
With the above configuration, the flash disk device of the embodiment operates as follows. This operation will be described with reference to the operation flowchart of FIG. Since steps S21 to S30 are the same as steps S1 to S10 of the first embodiment, the description thereof will be simplified. Further, since the read operation and the write operation are the same as those of the prior art, description thereof is omitted for the sake of brevity.

  When there is no access from the host machine 1 for a certain period of time, or when the number of empty blocks in the flash memory falls below a certain amount, the garbage collection operation is started.

  When the garbage collection operation is started, the garbage collection is started from the beginning by referring to the chip number X and the block number Y at which garbage collection is started in the garbage collection start position storage unit 40, that is, X = 1, Y = 1 (step S20), if it is not garbage collection from the beginning, set the chip number to start garbage collection as X and block number Y (step S33), proceed to step S25 described later, unused A garbage collection operation is executed according to the number of blocks.

  On the other hand, in step S20, when the chip number X and the block number Y for starting garbage collection in the garbage collection start position storage unit 40 are X = 1 and Y = 1, respectively, As in the first embodiment, steps S21 to S24 described below are performed.

  That is, the temporary storage page list 34 of FIG. 5 showing the state of each page is created for a predetermined number of blocks, and an unused flag is set in the temporary storage page list 34 corresponding to the page 22 that is not used in the address table 30. The unused block is erased for all pages, all the flags of the corresponding page are erased, and the erased chip number and block number are the number of unused pages in the unused page management table 32 of FIG. Is written into the index of 0xFFFFFFFF having a smaller index. Then, the unused page management table 32 of FIG. 3 is created for each block of used pages with reference to the temporary storage page list 34 for each number of unused pages. (Steps S21 to S24)

  Then, it is determined whether the number of unused pages in the unused page management table 32 is 32, that is, whether the number of unused blocks is equal to or larger than a certain amount. If the total number of unused blocks is equal to or larger than a certain amount, Since the garbage collection operation is unnecessary, the present process is terminated as it is (step S25).

  On the other hand, if there are not more than a certain number of unused blocks, a garbage collection operation is necessary. Therefore, a block with many unused pages is not used except when all the blocks are unused (that is, 32 unused pages). Extracted by the used page management table 32, the used page data of the block having many unused pages is read, and an unused flag is set in the corresponding chip number and block number of the temporary page list 34 (steps S26 to S28).

  Next, the read data is referred to the unused page management table 32, a block having a large number of unused pages is preferentially selected, a block having a large index is preferentially written, and the read data is written to the selected block. Along with the movement between blocks, the correspondence between the logical sector number of the address table 30 and the physical page is updated (steps S29 and S30).

  Then, it is determined whether or not all the predetermined blocks have been carried out (step S31). When the garbage collection of all the blocks has not been completed, the process returns to the aforementioned step S23, and the data movement is performed in steps S23 and S24. The generated unused block is erased, and the erased chip number and block number are written into the index of 0xFFFFFFFF having a smaller index in the unused page management table 32. Then, the unused page management table 32 of FIG. 3 is created for each block of used pages with reference to the temporary storage page list 34 for each number of unused pages.

  In step S25, the number of newly generated unused blocks is confirmed again. When a predetermined number or more of unused blocks are secured, this processing is terminated as it is.

  On the other hand, when it is determined in step S25 that a predetermined number or more of unused blocks have not been secured, the operations of steps S26 to S31 and S23 to S25 are repeated until a predetermined number or more of unused blocks can be secured.

  When the processing for the predetermined number of blocks is completed in the above-described step S31, the chip number X and the block number Y for starting garbage collection are updated so that garbage collection is performed for the next predetermined number of blocks. The updated chip number is stored in X and the block number is stored in Y.

  When the block number becomes equal to or greater than the number L of all blocks of each chip by the above update, the chip number X is updated, the block number is updated to Y = 1, and stored in the garbage collection start position storage unit 40. .

  If it is determined that the garbage collection of all the chips and all the blocks has been completed, the chip number and the block number Y for starting the garbage collection are initialized, and X = 1 and Y = 1, and the garbage collection start position storage unit 40 And this processing is terminated (step S32).

  In the above description of the embodiment, the garbage collection is performed for each predetermined number of blocks. However, the predetermined number of blocks may be changed as appropriate.

(Effect of Example 2)
As described above, according to the flash disk device of the second embodiment, garbage collection is performed for each predetermined number of blocks, and when the garbage collection process is completed, the chip number and the block number are updated and stored. When collection start position storage means is provided and garbage collection is started, garbage collection is carried out from the position stored in the garbage collection start position storage means. Thus, the garbage collection processing time can be further shortened.

<< Other modifications >>
In the above description of the embodiment, the management table storing the chip number and the block number corresponding to the number of unused pages is used as shown in FIG. 3, but the chip number and the block corresponding to the number of used pages are reversed. A management table for storing numbers may be used.

  In the above description of the embodiment, the temporary storage page list 34 is stored in the RAM 11a and the garbage collection start position storage unit 40 is stored in the nonvolatile memory 12. However, the temporary storage page list 34 is stored in the nonvolatile memory 12. It may be stored in the memory 12 or the garbage collection start position storage unit 40 may be stored in the flash memory 20.

  The present invention can be widely used in flash disk devices using flash memory.

1 is a diagram illustrating a configuration of a flash disk of Example 1. FIG. 1 is a diagram illustrating a memory configuration of a flash memory according to Embodiment 1. FIG. FIG. 6 is a diagram illustrating a configuration of an unused page management table in the flash memory according to the first embodiment. 1 is a diagram illustrating a memory configuration of a flash memory according to Embodiment 1. FIG. FIG. 3 is a configuration diagram of a temporary storage page list according to the first embodiment. FIG. 3 is an operation flowchart of the flash disk device according to the first embodiment. 6 is a diagram illustrating a memory configuration of a flash memory according to Embodiment 2. FIG. FIG. 10 is an operation flowchart of the flash disk device according to the second embodiment. It is a figure explaining the structure of the unused page list | wrist of the conventional flash memory.

Explanation of symbols

10 Flash disk device 11 MPU
16 Flash memory controller 20 Flash memory 21 Block 22 Page 30 Address table 32 Unused page management table 33 Block management table 34 Temporary storage page list 40 Garbage collection start position storage unit

Claims (2)

A flash disk device having a plurality of blocks, which are write units composed of a plurality of pages,
Provide an unused page management table that stores the corresponding block number for each number of unused pages.
A flash disk device characterized in that garbage collection processing is performed from a block having a large number of unused pages using the unused page management table. The block constitutes a chip for each predetermined number of blocks,
2. The flash disk device according to claim 1, wherein the unused page management table stores a chip number and a block number corresponding to the number of unused pages.

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