SD-MMC writing FAT

Hi All,

I am starting some work that would be using an SD card (in MMC-SPI
mode) and I was hoping to use a PIC or similar low memory chip.

The idea was to use Lewin Edward's DOSFS (www.zws.com) as it only
requires about 1KB RAM.

The problem is that according to the SANDISK spec one can do sector
writes of 512 bytes, but that an erase will operate on 32 sectors. This
means that to update the directory or the FAT one needs to read out
16KB of data, do the erase, update the byte(s) in ram and write it all
back again. This 16K block won't fit in a PIC.

Have I misunderstood the requirements relating to SD / MMC for updating
a sector?

--Rocky

.

Relevant Pages

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