MD3331-D64-V3 M-Systems Inc., MD3331-D64-V3 Datasheet - Page 32

• Manufacturer Part Number: MD3331-D64-V3
• Description: Diskonchip Millennium Plus
• Manufacturer: M-Systems Inc.

DiskOnChip Millennium Plus 16/32/64MByte
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 Millennium Plus as the boot replacement device, TrueFFS SDK also incorporates in its
source code the BDK, software that is required for this configuration (this package is also available separately).
Please refer to the Boot Software Development Kit (BDK) developer guide for further information on using this
software package.
6.1.3 File Management
TrueFFS accesses the flash memory within DiskOnChip Millennium 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 File
Allocation Table (FAT) file system, the data stored on DiskOnChip uses FAT-16.
Note:
DiskOnChip Millennium Plus is shipped unformatted and contains virgin media.
6.1.4 Bad-Block Management
NAND flash being 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. The
Bad Block Table in DiskOnChip Millennium Plus is hardware-protected for ensured reliability.
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 Millennium Plus, the erase cycle limit of the flash is 1M erase cycles
(commercial temperature) or 300,000 (extended temperature). This means that after approximately 300,000 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 is
more and more noticeable as the flash media becomes full.
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Data Sheet, Rev. 1.7
93-SR-002-03-8L