CSD is usually 512 (well, 9), but for 2GB (and the rogue 4GB SD cards)
it is 1024 (or 2048 for 4GB). This value doesn't work for the block
read commands (which really want 512). Hardcode 512 for those. This
may break really old MMC cards that don't have a 512 block size (I've
never seen one: make my day and send me one :-), but since the MMC
side of the house is currently broken, it should only have the effect
that 2GB (and non-conforming 4GB) SD cards will work.
My 'non-conforming' 4GB SD card also works now too. The
non-conforming 4GB SD cards were sold for a while before the SD
association was worried they would be (a) incompatible (different FAT
flavor on them) and (b) confusing for the new SDHC standard and
cracked down on suppliers' bogus use of the SD trademark...
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