The NVS.h defines NVS_lock() and NVS_unlock() as well as function pointer entries for these. The NVS.c file however, does not implement these functions even though device specific implementations exist. The only driver that seems to not implement these is the CC32XX version, while all others actually have these implemented and present in the function pointer table. As documentation suggest costumers should use these functions, they should be properly implemented on the top-level or a comment should be added that these APIs are not meant to be used.