NVENC for HEVC cannot initialize with B-Frame setting

I have tried so many ways to try to enable B-Frame for HEVC encoding. But all ways I tried failed. However, B-Frame can work if I use NVENC for H.264. So, does NVENC really support B-Frame? How can I enable it?

I am using Titan X card, Windows 8.1 64 bits, driver version 353.30.

Thank you very much.

Current Version HEVC encoder of NVENC does not support B-Frame

Is this a hardware limitation of the current cards or is it not yet done in the software ?