I have adapted AN4379 boot-loader for our product.
Upgrading the product firmware by copying an S19 image file to the product when enumerated as a hard drive has worked perfectly on Windows 7 and Windows XP.
Evaluating the same process on a Windows 8.1 machine results in a file copy failure near the end of the S19 file (seen on USB analyzer). There is still a significant number of S19 entries to send.
The process stops, and a reset is sent by the PC.
1. The boot-loader firmware has been adapted to remember root directory writes, and show up-to-date file names on the hard drive window.
2. The Bulk packet in/out sizes have been changed from 32 bytes to 64 bytes. This has not affected the described behavior.
3. The Windows 8.1 machine has been fully upgraded. Some Googling showed that system file USBSTOR.SYS has been changed recently due to complaints about external USB drives being powered down during use.
4. Trying to write a small S19 file (approx. 62kB vs. 800kB) still fails near the end of the file.
5. Kinetis K20 part.
Any suggestions would be most welcome!