Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-07-09
2003-08-05
Bragdon, Reginald G. (Department: 2188)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
Reexamination Certificate
active
06604168
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flash ROM management method and apparatus in, e.g., a computer. The present invention also relates to an IC card and an electronic camera using a flash ROM.
Various types of flash ROMs are currently available and roughly classified into those developed for flash disks and those developed for BIOSs of personal computers.
The erase unit of the former flash ROM is 512 bytes which is a general erase unit of hard disks. Therefore, this flash ROM is highly compatible with file systems. The erase unit of the latter flash ROM is a large block unit, e.g., 64 KB. Also, some of flash ROMs of this type require a voltage of 12 V or higher as a write voltage as in the case of PROMS. Although flash ROMs of the latter type are readily obtainable because they are inexpensive, they are not highly compatible with file systems and hence cannot be used as particularly small-capacity recording media.
As described above, flash ROMs designed for BIOSs are inexpensive and therefore readily available although they have a large erase unit and are not highly compatible with file systems. Accordingly, if this type of flash ROMs can be applied to file systems, inexpensive small-capacity recording media can be provided.
IC cards inserted into host apparatuses are widely used as auxiliary storages for storing various data. For example, an IC card which only reads out data, such as an IC card storing font data, incorporates a ROM storing necessary data. An IC card in which data is rewritable generally incorporates a RAM, and a data read/write operation is executed by using the RAM. Since, however, a RAM cannot hold data without being backed up by a power supply, a power supply is incorporated in an IC card if it is necessary to hold data.
A flash ROM is an example of the data rewritable ROM. Various types of flash ROMs are presently available and roughly divided into a category developed for flash disks and a category developed for BIOSs of personal computers.
Generally, IC cards require a dedicated interface, and so it is not possible to use interfaces for common file systems (e.g., hard disks and floppy disks) which host apparatuses have.
In electronic cameras, image data obtained by photography is stored in a storage medium such as an internal DRAM or an external memory card. These storage media need to be constantly backed up by, e.g., batteries since the stored contents disappear if the supply of power is cut off. A magnetic disk is an example of a storage medium which does not require electrical backup to hold the stored contents. However, magnetic disk devices are relatively large and therefore impair the portability of electronic cameras. Another example of a storage medium which need not be electrically backed up to hold the stored contents is a rewritable ROM, i.e., a flash ROM.
As described above, flash ROMs designed for BIOS have a large erase unit and a low compatibility with file systems but are readily obtainable because they are inexpensive. Therefore, if this type of flash ROMs can be applied to system files, it is possible to provide inexpensive, small-capacity, and small-sized recording media which do not require a power supply to hold the stored contents. This is convenient as a storage medium of an electronic camera.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flash ROM management method and apparatus capable of making a flash ROM with a large erase unit compatible with a file system.
The present invention has been made in consideration of the above situation, and has as its object to provide a flash ROM management method and apparatus which can manage a data read•write unit (storage unit) smaller than an erase unit in a flash ROM and can therefore make a flash ROM with a large erase unit compatible with a file system.
When the above object is achieved, even a flash ROM designed for BIOS and having an erase unit of 64 KB can provide a file system with services similar to those provided by a hard disk.
To achieve the above object, a flash ROM management apparatus according to the present invention comprises access means for accessing a plurality of data areas and management areas corresponding to the data areas formed in a flash ROM, writing means for receiving a write instruction containing specification information which specifies a data write destination, writing data in one of the data areas, and writing the specification information in a management area corresponding to the data area, and reading means for receiving a read instruction containing specification information which specifies a data read source, retrieval-accessing a management area in which the specification information is stored, and reading out data stored in a data region corresponding to the retrieval-accessed management area.
Preferably, the management area stores state information indicating whether a corresponding data area is writable, and the writing means retrieval-accesses a management area whose state information indicates a writable state, writes the specification information in the retrieval-accessed management area, and writes data in a data area corresponding to the retrieval-accessed management area. When data in the flash ROM is updated, for example, the updated data can be written in an appropriate data area by checking the state information.
Preferably, the management area stores state information indicating one of at least three states, i.e., an unused state indicating that a corresponding data area is writable, a busy state indicating that data written in the data area is valid, and a used state indicating that the data written in the data area is invalid, and the writing means retrieval-accesses a management area whose state information indicates the unused state, writes the specification information and data in the retrieval-accessed management area and a corresponding data area, respectively, and changes the state information of the management area to the busy state. Since one of the three states, the busy, used, and unused states, is indicated for each data area, an area in which data can be written and an area in which valid data exists can be known by checking the state information. Consequently, the stored data in the flash ROM can be more appropriately managed.
Preferably, the writing means retrieval-accesses a management area having specification information contained in the write instruction and changes state information of the retrieval-accessed management area to the used state. When the contents of a data area specified by certain specification information are updated, it is possible to clearly show that the data is the one before the updating (i.e., unnecessary data). Consequently, appropriate storage management can be performed.
Preferably, the apparatus further comprises moving means for retrieval-accessing all management areas whose state information indicates the busy state in an erase block as an erase unit of the flash ROM and moving contents of the retrieval-accessed management areas and corresponding data areas to the outside of the erase block, and erasing means for erasing the erase block after the execution of the moving means. Consequently, a data area in the used state in which data is made invalid by, e.g., updating of the data, can be changed into a writable unused data area. This improves the utilization of the flash ROM.
Preferably, a moving destination of the contents of the management area and the data area which are to be moved by the moving means is another erase block in the flash ROM. Since data is moved inside the flash ROM, the data is safely held even if the power supply is turned off.
Preferably, the moving means determines the moving destination as a random access memory when no writable data area exists in other erase blocks of the flash ROM. Even when all data areas in the flash ROM are busy or already used, an unused data area can be formed in the flash ROM. As a consequence, the flash ROM can be efficiently used.
Preferably, a moving destination of the c
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