> I am really surprised there isn't a linux command out there that allows you to send low-level CMD's to an MMC controller. I thought mmc-utils did. It does --

> I am really surprised there isn't a linux command out there that allows you to send low-level CMD's to an MMC controller. I thought mmc-utils did. It does -- but the problem is that there are very few readers out there that are supported by the Linux mmcblk driver. Most of them just present themselves to the system as generic USB block devices. > Does SD card firmware mark blocks as belonging to a specific "Application Unit"? Yup. Basically cards are divided up into application units, and application units are divided up into recording units. Where they're physically located on the card is opaque to the host -- so yeah, it can rearrange them as needed.