Spencer:

I think you should take a hard look at the requirement that has been placed upon the target device to have an uninterrupted file transfer.

You should allow for sporadic delays in the data transfer and then cover the case for recovery of a hang via timeout logic in the target. Use timeouts on order of seconds which are fast with respect to user but are slow with respect to the USB blocking.

You may also want to consider some redesign to allow the host downloader end to fragment the file into blocks and wrap some validity checking and sequence numbering around the blocks. Then make the target capable of getting individual blocks and programming them individually. (A good size to use for this is the native programming page size of the FLASH not the erase block size.). In my opinion this will give you way more compliance to occasional stops and spurts in the data flow and permit you to insert easy block level re-try into the transfer process to give an overall more reliable appearing experience to the user.

Michael Karas