JP4105179B2 - Data management method - Google Patents

Description

  The present invention relates to a data management method for a flash memory, and more particularly to a data management method capable of making the access time to the latest data almost constant regardless of the number of data updates.

  There is a flash memory as a medium for recording data. In a flash memory, generally, a logical value in an erased state is described as 1, and a logical value when written is described as 0.

  When updating data, it is necessary to erase (0 → 1) and write (1 → 0) once. However, since erasing requires 100 times or more time of writing, it takes time to newly write data after erasing data.

  Therefore, a technique that does not erase old data when updating data has been proposed (for example, Patent Document 1 or Patent Document 2). In this technique, when data is updated, the “next physical address portion” is attached to the old data, and the update data is written in the location indicated by the “next physical address portion”. When updating again, the process is repeated. Further, at the time of reading, the latest data is found by tracing the address described in the “next physical address portion” from the beginning, and the data is read. As a result, data change is not accompanied when data is changed, and the change time can be shortened.

JP 2002-196976 A JP 2003-122646 A

  However, the conventional technique has a problem that it takes time to access the latest data because the number of addresses to be tracked increases every time data is updated.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a data management method capable of making the access time to the latest data almost constant regardless of the number of data updates in the flash memory. To get.

In the data management method according to the present invention, when a plurality of buffers are arranged in an array in a flash memory and data is written, the data to be written is written in order from the first buffer of the plurality of buffers, and the data to be written When writing all the addresses of the buffer where the data was written in order to the next buffer of the buffer where the data was written, and rewriting the old data with new data, the new data is stored in the empty buffer next to the written buffer group. In the buffer next to the buffer where the new data was written, the address of the buffer where the old data was written out of all the addresses of the buffer where the data before rewriting was written is replaced with the address of the buffer where the new data was written, The bar to which the data to be read is written Write all address of fur in order. Other features of the present invention will become apparent below.

  According to the present invention, since all addresses of data to be read are always at the end of the written buffer group, the access time to the latest data can be made almost constant regardless of the number of data updates in the flash memory.

Embodiment 1 FIG.
Hereinafter, the data management method according to the first embodiment of the present invention will be described with reference to FIG.

  First, as shown in FIG. 1A, a plurality of buffers A, B, C,... That are writable areas are arranged in an array in the flash memory. Next, when writing one piece of data, for example, data 1 is written to the buffer A at the address α. Then, the address α is written in the first write location of the next buffer B. Thereby, at the time of reading, the data 1 written in the address α can be read by accessing the buffer B.

  When writing a plurality of data, the data to be written is written one by one for each buffer in order from the top buffer of the plurality of buffers. When the size of data to be written is larger than one buffer size, it is possible to write one data in a plurality of buffers. In this case, the start address of the written data may be written. However, if there are other buffers where addresses have already been written, all addresses are copied and written from there. For example, as shown in FIG. 1B, data 1 is written into buffer A at address α and data 2 is written into buffer B at address β. Then, the address α is written in the first writing location of the next buffer C, and the address β is written in the second writing location.

  When writing a plurality of data in this way, all addresses of the buffer in which the data is written are sequentially written in the next buffer. Thus, when data is read, the target data can be read by accessing the buffer in which the address is written.

  Next, a case where old data 1 written in the buffer A is rewritten with new data 11 will be described. First, as shown in FIG. 1C, new data 11 is written in the empty buffer D next to the written buffer group A to C. Further, all the addresses of the buffer in which the data to be read are written are sequentially written in the next buffer E.

  At that time, the address γ of the buffer D to which the new data 11 is written is written instead of the write location (first) of the address α of the buffer A to which the old data 1 has been written. Thereby, it can be determined that the data 11 is rewritten to the data 1.

  For data 2 whose data is not new, the address β written in the second writing location of the buffer C is copied as it is to the second writing location of the buffer E.

  As a result, since all addresses of data to be read are always at the end of the written buffer group, the access time to the latest data can be made substantially constant regardless of the number of data updates in the flash memory.

Embodiment 2. FIG.
Hereinafter, a data management method according to Embodiment 2 of the present invention will be described with reference to the drawings.

  First, as shown in FIG. 2, the same number of flags a, b, c... As the plurality of buffers A, B, C. 1-to-1 correspondence with these buffers. Then, a value indicating the state of the corresponding buffer is entered in each flag. In at least one of the flags, a value indicating the location of the buffer in which all addresses of data to be read are written is entered.

  A binary search is performed when searching for the flag value at the time of writing or reading. As a result, even when the number of updates increases, the access time to the latest data becomes substantially constant.

  A flow when data is written will be described with reference to FIG. However, the flag is 2 bits, the value of the flag that is not written in the corresponding buffer is “11” (unused), and the value of the flag that is written in the buffer is “10” (used) The flag value in the state where the address is written in the buffer is “00” (address stored).

  First, a binary search is performed for a flag, and a flag corresponding to a writable buffer is searched. Here, the search condition is “unused flag at the top”. As shown in FIG. 3A, when the flag a is “11” (unused), the buffer A corresponding to the flag a can be written.

  Next, as shown in FIG. 3B, the flag a is changed from “11” to “10”. Then, as shown in FIG. 3C, data is written into the buffer A (address α) corresponding to the flag a. Since the number of data to be written in one buffer is one, when writing a plurality of data, the data is written in the same procedure in the next buffer. Here, the flag b is changed from “11” to “10”, and data 2 is written to the buffer B (address β).

  After all the data has been written, the address is written in the buffer next to the buffer in which the data has been written. Here, after the flag c is changed from “11” to “10”, the addresses α and β of the buffer A in which the data 1 is written and the buffer B in which the data 2 is written are sequentially written in the buffer C. At this time, it is made clear where each address is written in the buffer C. Here, as shown in FIG. 3D, the address α is written to the first writing location of the buffer C, and the address β is written to the second writing location of the buffer C. After all addresses have been written, the flag c is changed from “10” to “00” as shown in FIG. 3E to indicate that the address has been written to the buffer C.

  Next, the flow when rewriting old data to new data will be described with reference to FIG. First, before rewriting, as shown in FIG. 4A, data 1 is written to the buffer A (address α), data 2 is written to the buffer B (address β), and the first address α in the buffer C is written. Second, the address β is written. The old data 1 written in the buffer A is rewritten to new data 11 as follows.

  First, a binary search is performed in the same manner as in writing to search for a flag corresponding to a writable buffer (here, flag d). Then, as shown in FIG. 4B, the value of the flag d is changed from “11” to “10”, and the data 11 is written to the corresponding buffer D (address γ).

  Next, as shown in FIG. 4C, after data is written, the flag e corresponding to the next buffer E is changed from “11” to “10”. Then, the address γ is written in the first writing location of the buffer E, and the address β is written in the second writing location. That is, the address γ is written in the write location (first) where the address α was written in the buffer C. Further, the address β of the buffer B that has not been rewritten is written to the write location (second) where the address is written in the buffer C also in the buffer E. Thereafter, as shown in FIG. 4D, the value of the flag e is changed from “10” to “00” to indicate that the address is written.

  Next, a flow when data is read will be described with reference to FIG. As shown in FIG. 5A, the flash memory has data 1 in buffer A (address α), data 2 in buffer B (address β), address α and address β in buffer C, and buffer D (address γ). The data 11 in which the data 1 is rewritten, and the address γ and the address β are written in the buffer E.

  Similar to the writing of data, the flag is searched in half and a writable flag is searched. Here, as shown in FIG. 5B, the flag f is an unused flag at the head. Therefore, the flags whose flag value is “00” are searched one by one from the flag e toward the head. Then, as shown in FIG. 5C, the latest data data 11 and data 2 are read by accessing the address γ and the address β written in the buffer E corresponding to the flag e having the value “00”. .

  As a result, as in the first embodiment, since all addresses of data to be read are always at the end of the written buffer group, the access time to the latest data is almost the same regardless of the number of data updates in the flash memory. Can be constant. Further, by performing a binary search when searching for the flag value, the search time is within a certain time regardless of the location of the flag value.

  Specifically, the time required to read 1k binary data is 55.4 ms in the prior art, but can be reduced to 17.4 ms in the present invention. The time required for writing 1k binary data is 575.4 ms in the prior art, but can be reduced to 49.2 ms in the present invention.

  The flag is not limited to being installed in the flash memory, but may be installed outside the flash memory. In this case, after completion of the writing process, information indicating how far the buffer has been used can be held continuously by copying the flag outside the flash memory into the flash memory. Further, the flag state does not need to be displayed with 2 bits, and it is only necessary to display a three-stage state.

Embodiment 3 FIG.
In the first and second embodiments, the buffer in which the latest data is written is accessed by referring to the address of the buffer in which the data is written. On the other hand, in the third embodiment, the address ε and the address ζ are written in the buffer G as shown in FIG. An address α and an address β are written in the address ε, and an address γ and an address δ are written in the address ζ. That is, the addresses ε and ζ of the buffers C and F in which the addresses of data to be read are written are written in the buffer G. Thereby, more data can be referred.

  In FIG. 6, the values of the flag c and the flag f are “10”. This is the case where information is written in the buffers C and F as normal information, not as address information. On the other hand, when information is written in the buffers C and F as address information, the value of the corresponding flag is set to “00”. In this case, the address information to be written in the buffer may include the address hierarchy information so that the address information is an upper layer or a lower layer.

It is a figure for demonstrating the data management method which concerns on Embodiment 1 of this invention. It is a figure which shows the buffer and flag which are used with the data management method which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the flow at the time of writing the data in the data management method which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the flow at the time of rewriting the old data by new data in the data management method concerning Embodiment 2 of this invention. It is a figure for demonstrating the flow at the time of reading the data in the data management method which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the data management method which concerns on Embodiment 3 of this invention.

Claims (3)

Arrange multiple buffers in the flash memory in an array,
When writing data, the data to be written is written in order from the first buffer of the plurality of buffers, and all addresses of the buffer to which the data has been written are sequentially written to the buffer next to the buffer to which the data to be written is written. Write on the
When rewriting the old data to the new data, writing the new data to a free buffer in the following written buffer group, the next buffer of the buffer is written to the new data, the data before rewriting The address of the buffer in which the old data is written is replaced with the address of the buffer in which the new data is written out of all the addresses in the written buffer, and all addresses of the buffer in which the data to be read are written are sequentially written. Data management method. The same number of flags as the plurality of buffers are provided in a certain size,
The plurality of flags correspond to the plurality of buffers on a one-to-one basis,
2. The data management method according to claim 1, wherein a value indicating a location of a buffer in which all addresses of data to be read are written is placed in any of the plurality of flags.   The data management method according to claim 2, wherein a binary search is performed when searching for the value of the flag.

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