Aha, very good! Yes, I had seen the second link -- and, in fact, posted on the Soft-Center forums at the time. It gave me some of the basic information, but sadly, without the "key" to what some of that means, it's not terribly useful to me :-( for instance, I'm still not sure what "xor 0186" means, and how that translates to the whitening scheme I saw.

The "Update size" and "Update enable" did give me the idea to do what I called 'sector updates'. Do you have any more information on how those work?

I didn't have that 'usbdev.ru' site at the time. That page seems specific to the USB versions, not the SD card (SM2683) parts; unfortunately, I speak very little Russian. Do you have any particular parts I should ook at?

Thanks so much for any help you might be able to provide! I'd like to fill in the blanks in my knowledge of these things; in particular, I'd feel a lot more comfortable if I knew how the sector updates worked...