MD2241-D128-V3 M-Systems Inc., MD2241-D128-V3 Datasheet - Page 22

• Manufacturer Part Number: MD2241-D128-V3
• Description: Diskonchip Dimm Plus
• Manufacturer: M-Systems Inc.

DiskOnChip DIMM Plus
6.1.2 TrueFFS Software Development Kit (SDK)
The basic TrueFFS Software Development Kit (SDK) provides the source code of the TrueFFS driver. It can be used
in an OS-less environment or when special customization of the driver is required for proprietary OSs.
When using DiskOnChip DIMM Plus as the boot replacement device, TrueFFS SDK also incorporates in its source
code the Boot SDK, software that is required for this configuration (this package is also available separately). Please
refer to installation manual IM-DOC-020 Boot SDK for further information on the usage of this software package.
6.1.3 File Management
TrueFFS accesses the flash memory within DiskOnChip DIMM Plus through an 8KB window in the CPU memory
space. It provides block device API, by using standard file system calls, identical to those used by a mechanical hard
disk, to enable reading from and writing to any sector on DiskOnChip. This makes it compatible with any file
system and file system utilities such as diagnostic tools and applications. When using the Flash Allocation Table
(FAT) file system, the data stored on DiskOnChip uses FAT-16.
Note:
Please note that DiskOnChip DIMM Plus is shipped unformatted and contains virgin media.
6.1.4 Bad Block Management
Since NAND flash is an imperfect storage media, it contains some bad blocks that cannot be used for storage
because of their high error rates. TrueFFS automatically detects and maps bad blocks upon system initialization,
ensuring that they are not used for storage. This management process is completely transparent to the user, who
remains unaware of the existence and location of bad blocks, while remaining confident of the integrity of data
stored.
6.1.5 Wear-Leveling
Flash memory can be erased a limited number of times. This number is called the erase cycle limit or write
endurance limit and is defined by the flash array vendor. The erase cycle limit applies to each individual erase block
in the flash device. In DiskOnChip DIMM Plus, the erase cycle limit of the flash is 100,00 erase cycles. This means
that after approximately 100,00 erase cycles, the erase block begins to make storage errors at a rate significantly
higher than the error rate that is typical to the flash.
In a typical application and especially if a file system is used, a specific page or pages are constantly updated (e.g.,
the page/s that contain the FAT, registry etc.). Without any special handling, these pages would wear out more
rapidly than other pages, reducing the lifetime of the entire flash.
To overcome this inherent deficiency, TrueFFS uses M-Systems patented wear-leveling algorithm. The wear-
leveling algorithm ensures that consecutive writes of a specific sector are not written physically to the same page in
the flash. This spreads flash media usage evenly across all pages, thereby maximizing flash lifetime. TrueFFS wear-
leveling extends the flash lifetime 10 to 15 years beyond the lifetime of a typical application.
Dynamic Wear-Leveling
TrueFFS uses statistical allocation to perform dynamic wear-leveling on newly written data. This not only
minimizes the number of erase cycles per block, it also minimizes the total number of erase cycles. Because a block
erase is the most time-consuming operation, dynamic wear-leveling has a major impact on overall performance. This
impact cannot be noticed during the first write to flash (since there is no need to erase blocks beforehand), but it is
more and more noticeable as the flash media becomes full.
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Preliminary Data Sheet, Rev. 1.2
94-SR-002-08-8L