Storage device and accessing method

Details Storage device and accessing method Storage device and accessing method

1999-07-28

2002-11-05

Yoo, Do Hyun (Department: 2187)

Electrical computers and digital processing systems: memory

Address formation

Address mapping

C711S203000, C365S185290, C365S185330

Reexamination Certificate

active

06477632

ABSTRACT:

TECHNICAL FIELD
This invention relates to a storage device and an accessing method, and particularly to a block erase type storage device and an accessing method for the same.
BACKGROUND ART
A block erase type storage device is known which comprises a block erase type storage medium such as a flash memory, and which reads and writes information under the control of a central processing unit (CPU) and a dedicated controller.
The block erase type storage medium indicates such a storage medium that the storage contents of a writing target area need to be erased in advance in order to write data therein and an erasing process can be performed only in units (generally called blocks) equal to or larger than the smallest unit (generally called a page, a segment or the like) of the storage capacity dealt in a writing process.
In order to manage an external access, the block erase type storage device comprises an SRAM (Static Random Access Memory) or the like which stores an empty block table in which information representing the locations of empty blocks is stored and an address translation table in which information showing the correspondence between logical and physical addresses is stored.
Upon reception of a write request, the block erase type storage device finds an empty block registered in the empty block table, writes data in the found block, adds the correspondence between the physical and logical addresses of the block to the address translation table, and furthermore, erases the block from the empty block table.
Moreover, upon reception of a read request, the block erase type storage device searches the address translation table while using the logical address of to-be-read data as a key, discriminates the physical address of the location at which the to-be-read data has been stored, and reads the data from that location.
In to such a storage device, the volume of the entire storage device increases according to the volume occupied by the SRAM. Due to this, such a storage device when used for purposes which require a small volume as in the case of a JEIDA/PCMCIA card, etc., needs a volume suppressing idea.
Furthermore, the SRAM consumes a large amount of power, and if the SRAM is used to store a variety of tables, the amount of power consumed by the entire storage device increases, entailing a drawback of the storage device becoming unsuitable for being applied to purposes which require low power consumption as in the case of a JEIDA/PCMCIA card, etc.
DISCLOSURE OF INVENTION
This invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a block erase type storage device of a small volume and low power consumption and an accessing method for the same.
A storage device according to the first aspect of this invention having the above object is characterized by comprising:
storage means (
1
), including a plurality of memory blocks to which physical addresses have been assigned;
erasure means (
1
e
) for batch erasing of stored data from the storage means in units of memory blocks; and
writing means (
4
X,
4
B,
5
,
20
), to which data and logical addresses are input, for determining locations where the data is to be stored in the storage means and for writing the data in the locations;
wherein the storage means stores an address translation table which stores information showing a correspondence between the logical addresses and physical addresses of the storage means, and
the writing means comprises means (
4
X,
4
B,
5
,
20
) for adding, to the address translation table, information showing a correspondence between physical addresses of the locations where the data has been written and the input logical addresses, or for updating the address translation table.
According to the storage device having this structure, the address translation table is stored in the storage means which is a block erase type storage medium. Therefore, a storage medium such as an SRAM or the like for storing the address translation table is not required in addition to the aforementioned storage means. This ensures a block erase type storage device whose volume is relatively small and whose power consumption is low.
The above-described storage device may further comprise reading means (
4
X,
4
B,
5
,
20
) including:
means (
20
) for storing a physical address of a block in which the address translation table has been written;
physical address reading means (
4
X,
4
B,
5
,
20
) for accessing the block which contains the address translation table stored therein and for reading physical addresses corresponding to logical addresses of to-be-read data; and
means (
4
X,
4
B,
5
,
20
) for reading and outputting data stored at the physical addresses read by the physical address reading means.
Using this reading means, the physical addresses of the to-be-read data can be detected and read from the address translation table stored in the storage means.
The aforementioned storage means can store an empty block table which stores information specifying empty blocks containing no data stored therein.
By employing this structure, the used amount of memory such as an SRAM or the like, utilized in addition to the storage means, can be further reduced to promote a reduction in the volume and power consumption.
The empty block table which stores information specifying the empty block that has been existed until the data has been stored in the empty block is eliminated, and the empty block table which stores information specifying empty blocks that remain after the empty block writing means has written the data in the empty block is stored in the storage means. By so doing, information on the empty blocks contained in the empty block table is updated so that the up-to-date empty block information can be attained at any time.
The aforementioned storage means may comprise a plurality of chips or flash memories, for example. In this case, the address translation table (and the empty block table) may be stored in an arbitrary block of any one of the chips or flash memories. And means may be provided for storing information showing in which block of which chip the address translation table and the empty block table have been stored.
The storage means stores the address translation table and the empty block table in one block.
According to this structure, the number of blocks for storing the address translation table and the empty block table can be minimized to one, and the storage capacity of the storage means can be used with efficiency. Moreover, the management of the locations at which those tables have been stored becomes easy.
Further, a storage device according to the second aspect of this invention is characterized by comprising:
storage means (
1
), including a plurality of memory blocks to which physical addresses have been assigned;
erasure means (
1
e
) for batch erasing of stored data from the storage means in units of memory blocks; and
writing means (
4
X,
4
B,
5
,
20
), to which to-be-written data and logical addresses are input, for determining locations where the data is to be stored in the storage means and for writing the data in the locations;
wherein the storage means stores empty block information specifying empty blocks in which the data is not stored, and
the writing means writes the data in an empty block specified by the empty block information.
According to this structure, the empty block information is stored in the storage means which is a block erase type storage medium. Therefore, a storage medium such as an SRAM or the like for storing the empty block information is not required in addition to the aforementioned storage means. This ensures a block erase type storage device whose volume is relatively small and whose power consumption is low.
If the writing means further comprises updating means (
1
e,
4
X,
4
B,
5
,
20
) for changing the empty block information stored in the storage means to the empty block information which specifies information on empty blocks that remain after the writing means has written the dat

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