[ECOS] FAT on NOR/ NAND flash
Ross Younger
wry@ecoscentric.com
Wed May 26 10:17:00 GMT 2010
viren.dobariya wrote:
> I am trying to port FAT on NOR flash of EA2468 board.
Running FAT on a raw flash device is not a good idea. I would suggest
that you use a different filesystem more suited to flash memory parts -
jffs2 and yaffs come to mind - or, if you really insist on using FAT,
implement a flash translation layer including wear levelling.
FAT was designed for media with small (often 512 bytes) sectors which
are individually rewritable (floppy drives, hard drives); NOR flash
devices can only be erased at the block level (64k or more). You'll have
an awful lot of trouble making it work properly. Because of this it is
also quite dangerous: the length of time taken to erase and reprogram a
whole block is much longer than it takes to write a sector to magnetic
media, leaving you very vulnerable to power supply issues.
Furthermore, the filesystem stores its file allocation table at fixed
sector locations. This leads to those regions of your flash device
experiencing a disproportionate amount of use; they will likely wear out
quickly, rendering your filesystem useless.
Ross
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