Quote Originally Posted by swingtan View Post
It's going to be hard to implement firmware and boot-block from the SD card without a big rewrite (I think). Currently there would be code to allow the FW and BB to be transfered over the USB link, so it would need to be rewritten to support the SD card filesystem. That means I/O support for the SD card controller as well as filesystem structures. It's not impossible, as many out devices will do at least firmware updates from a memory card (Canon cameras for one).

Simon.
Correct. It will never be possible to do firmware upgrades via the SD Card. The SD Card interface code and the FAT file system code is part of the firmware and is not available for execution while the firmware is being updated.
The USB comms is part of the boot block and operates independently of the firmware so USB comms is available while the firmware is being updated.

Regards
Paul