Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2000-05-09
2003-01-28
Robertson, David L. (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
Reexamination Certificate
active
06513095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a file system incorporating a non-volatile semiconductor memory device such as a flash memory, and a method for managing such a file system.
2. Description of the Related Art
In recent years, much attention has been paid to techniques for employing a non-volatile semiconductor memory device which is capable of electrically writing and erasing data therein (e.g., a flash memory) as an alternative drive for hard disk drives, which are capable of magnetically writing and erasing data therein.
Flash memories permit data reading at a rate which is about ten thousand times faster than that of hard disk drives, and data writing at a rate which is about one thousand times faster than that of hard disk drives. Other advantages of flash memories include their adaptability to be constructed in small size and with small weight, excellent shock resistance, and excellent portability. Flash memories are especially suitable for storing and reading small amounts of data at a fast rate.
However, flash memories have the following problems. Before writing new data in a storage region of a flash memory in which data is already written, it is necessary to erase existing data. A relatively long data erase time on the order of several dozen milliseconds to several seconds is required because data are deleted in units of several Kbytes. Moreover, flash memories can only guarantee that data can be safely written or erased up to a finite number of times.
In view of the aforementioned disadvantages of flash memories, in order to employ a flash memory as an alternative hard disk drive, it is necessary to provide a file system which is tailored to flash memories, i.e., a file system in which data are processed by units of several hundred bytes (as in hard disk drives) and in which data management is efficiently performed while minimizing data erasure. Such a file system is disclosed in Japanese Laid-Open Publication No. 6-95955, for example.
U.S. Pat. No. 5,544,119 discloses a processing method to be performed at the time when the power supply is restored after an interruption. U.S. Pat. No. 5,544,356 discloses a method for reconstructing a file system.
However, the aforementioned publications do not address situations where a flash memory or a file system for performing various processes may be used with a relatively unstable supply of power, e.g., in the case of using a battery as the power supply means. Hence, any unexpected interruption of the power supply, i.e., if the power supply is interrupted even for a short moment (e.g., due to exhaustion of the battery) during the operation of a flash memory or file system, may make it impossible to properly read the data stored in the flash memory.
The aforementioned problem will be more specifically described. Firstly, the current states of storage regions in which data can be stored (hereinafter referred to as “sectors”) are indicated by sector state information, which represents one of the three states “UNUSED” “IN USE”, or “INVALID”. Therefore, if an interruption of the power supply occurs during update of the data stored in a given sector, the data may incorrectly be recognized as being valid (i.e., not corrupt) even though the data has not been properly updated, based on the sector state information. This process of sector data update will be described with reference to a flowchart shown in FIG.
10
.
According to the flowchart shown in
FIG. 10
, the sector state information of a sector which stores existing data (supposing that this data is to be updated) is changed from “IN USE” to “INVALID” (Step
101
). Then, the sector state information of another sector is changed from “UNUSED” to “IN USE” (Step
102
). Thereafter, the update data is written to the sectors whose sector state information has been changed to “IN USE” (Step
103
). Steps
101
to
103
are repeated until there is no more data to be written.
If the power supply is interrupted immediately after Step
102
or during Step
103
, so that the writing of data to the flash memory is suddenly terminated, the sector state information of this sector remains to be “IN USE” although the writing of update data to this sector was not properly completed. Therefore, when the power supply is restored, the file system will incorrectly recognize the data stored in this sector as valid.
Secondly, if an interruption of the power supply occurs in the case where all of the data in one block of sectors (hereinafter referred to as a “target block”) is to be erased and thereafter the file system is reconstructed, it is possible that the same data may be left stored in two blocks, or all of the data in the one block may not have been completely erased. This file system reconstruction process will be described with reference to a flowchart shown in FIG.
11
.
According to the flowchart shown in
FIG. 11
, a block is previously secured or reserved as a reserve block, all of whose sectors have had their data erased so that the sector state information of all the sectors in that block indicates “UNUSED”. Then, any data within the target block that should be preserved is copied to the reserve block (Step
111
). That is, any data except for the data stored in the sectors whose sector state information indicates “INVALID” and the sector state information associated with such sectors must be copied to the reserve block. Furthermore, a block number of the target block, which is included in the location information other than the sectors whose sector state information indicates “INVALID”, overwrites the block number of the reserve block (Step
112
). Finally, the data in the target block (whose data was copied to the reserve block at Step
111
) is erased, and this block is secured as a reserve block for use in a subsequent file system reconstruction (Step
113
).
If the power supply is interrupted before the execution of Step
113
or during Step
113
, it is possible that the same data may be left stored in two blocks, or all of the data in one block may not have been completely erased, when the power supply is restored. As a result, it is impossible to secure a new reserve block.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a file system including at least one non-volatile semiconductor memory device, the at least one non-volatile semiconductor memory device including a plurality of erasure blocks, each erasure block including a plurality of sectors, wherein the file system includes: a file system memory section for storing block state information for each erasure block, the block state information representing one of a plurality of block states, and for storing sector state information for each sector, the sector state information representing one of a plurality of sector states: and a file system control section for, when accessing the at least one non-volatile semiconductor memory device, guaranteeing integrity of data already stored in the at least one non-volatile semiconductor memory device based on the block state information and on the sector state information in the file system memory section.
In one embodiment of the invention, the file system memory section is provided on a RAM having substantially no constraints concerning data updates, and the file system control section refers to the block state information and the sector state information stored in the RAM when accessing the at least one non-volatile semiconductor memory device.
In another embodiment of the invention, the plurality of block states represented by the block state information include the five states of “UNUSED”, “INCLUDES DATA”, “BLOCK FULL”, “RECEIVING DATA”, and “ERASING ORIGINAL BLOCK”, and the file system control section includes: means for changing the block state information of a first erasure block from “UNUSED” to “RECEIVING DATA”, the first erasure block being previously reserved as a reserve erasure block for use in a file system reconstruction process; means for transferring data stored in a second erasure b
Morrison & Foerster / LLP
Robertson David L.
Sharp Kabushiki Kaisha
LandOfFree
File system with assured integrity incorporating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with File system with assured integrity incorporating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and File system with assured integrity incorporating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3048806