I have a problem when trying to implement HFP client. Usually the android phone works as HFP ag role. But I want to make my android device work as the HF role, such as a normal headset. It seems that Google has added the HFP client code but I failed to make it. Now the A2DP works well, as it works as sink. But when I tried HFP, I can hear nothing in both side. The auto car project must finish the function i want but i cant find its source code. In addition, my test device is nexus 5 with android 5.0 and I can modify the rom if necessary. can anyone help? Just give a abc step. Thanks a lot!