Re: SD-MMC writing FAT

dalai lamah wrote:
Un bel giorno Rocky digitò:

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.

I don't remember if there is a specific MMC command to erase sectors,
anyway you don't need to erase a sector before writing it, you can just
overwrite it with the new data: the MMC controller will take care of all
the necessary operations (i.e. erasing a flash sector, rewriting the
unchanged blocks, etc) in a transparent way. You just have to be aware that
sometimes a sector write will take more time than the usual, because of all
these "hidden" operations.

Hi Antonio
Ok, so I did misunderstand what was meant. That would be why they go on
about it being more efficient if the data to be (over)written is the
size of an 'erase block'.
Thanks -- Rocky

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