ST72682 STMicroelectronics, ST72682 Datasheet - Page 14

• Manufacturer Part Number: ST72682
• Description: USB 2.0 high-speed Flash drive controller
• Manufacturer: STMicroelectronics

NAND Flash memory interface
4.2
4.2.1
4.2.2
4.2.3
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Bad block management
NAND memory manufacturers deliver their devices with factory-marked bad blocks. This
marking depends on the manufacturer and the NAND memory type (page size, memory
technology, etc.). The ST72682 supports all bad block markings currently available on the
market.
Bad Block identification
During firmware initialization, the MCU scans the entire NAND memory configuration to
identify bad blocks.
A bad block is defined as follows:
Bad block replacement
The firmware works on groups of 1024 blocks, called zones. A complete NAND
configuration can contain several zones:
The used blocks part is used to do a correspondence between NAND blocks and logical
address ranges.
This system allows all bad blocks to be masked from the Host. As a result, bad blocks are
never seen. Only a range of logical addresses are visible which correspond to the sum of
the used blocks part of all zones.
Late Fail block
During normal application life, defects may appear in the NAND memory. Under certain
conditions, these defects are not correctable and the corresponding block is declared as
“bad”.
In this case, new bad blocks are identified in the bad blocks part of the LUT and replaced by
new blocks from the “free blocks” part.
Five different block status bytes are considered: 4 status bytes from page 0 and 1 from
an other page (page 127 for MLC NAND; page 1 for SLC NAND).
The considered block is marked as a bad block if one out of these five bytes contains at
least four bits set to ‘0’.
Each zone is described in a Look Up Table (LUT) containing 1024 entries. A LUT is
composed of 3 parts: used blocks, free blocks and bad blocks.
The “bad blocks” part contains as many entries as the number of bad blocks identified
in that zone.
The “used blocks” part can have a size of 1000, 900 or 500 entries. This size is
configurable and also depends on the number of identified bad blocks.
The “free blocks” part contains the remaining entries.
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