Thread: Booting from MMC on N800 Now Available!!
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fanoush is offline fanoush
2007-02-20 , 08:56
Posts: 2,152 | Thanked: 1,490 times | Joined on Jan 2006 @ Czech Republic
#70
Originally Posted by DCr33P View Post
Why should there be at least one FAT partition on the mmc/sd card when booting from it? Ext2 is the boot partition with rootfs, so what's the FAT partition for?
it is easier this way, nokia system expect first partition to be FAT. it is also great for interoperability, other systems expect memory cards to be FAT too. For SD cards filesystem specification is even part of SD standard. All SD cards should be FAT (FAT16), all SDHC cards should be FAT32.

Originally Posted by DCr33P View Post
But what about ext2? If we are unlucky, we can wear out some specific blocks in a few months and had to suffer from read errors. Does the SD Controller have error correction?
As cards are expected to be FAT and this is very unfriendly filesystem for flash memory I wouldn't bother with ext2 :-)

SD/MMC memory cards (must) have its own internal logic for block management similar to hard disks. You can't tell which block is really used by the card when writing same block of filesystem. There are many reasons for this
- wear levelling and bad block management
- physical block size of NAND flash memory is different than filesystem block size and writing rules are much more complicated - blocks need to be written as a whole and erased before writing, it is better to handle this transparently inside card (i.e. pre-erase them and keep a pool of such fresh blocks ready for writing for better speed )