Hello, I am transferring a file using USB MSD to a device, based on the Keil USB library. Can I know, when the transfer starts, how many bytes to expect? What is the indication in software as to the "end of file"?
You miss these facts, a) The disk I/O system on most of OS has buffering to reduce frequent media access. The PC doesn't always read/write to media to access files/directories.
b) The disk I/O system is established on a presupposition that data on a media is never changed without the intervention of the system. When the device firmware modifies the data without command from the host, it may be regarded as disk error, or may be just ignored.
Many people (including me :-) ) have once thought MSC is handy way to implement data transfer over USB. But it's bad idea, actually.
Tsuneo