Could someone explain the bug-3243 problem?
If Indexed Mode register accesses are enabled, the ep0_rxstate() function calls musb_g_ep0_giveback() before writing to the CSR register. When control returns to this ep0_rxstate, the index register contents are over-written. This causes the CSR register write to fail. Fixed by writing the correct value into the index register before writing to the CSR. This was observed only in ep0_rxstate() with g_ether loaded and the device connected to a MS Windows host PC. Anticipatively fixed ep0_txstate() as well.