I am suffering a problem of USB DFU on MK20DN512VLL10, when I connect cable to PC, the PC always show "unknown USB device" rather than recognize it.
1. my DFU firmware can do USB_Reset_Service() function, but after it, it seems do nothing.
2. I set a break point at get descriptor function, but it doesn't break, so I think my firmware didn't receive the get_descriptor command.
what can I do next to fix the problem? please help. thank you!