Parrot bebop2 px4 v1.9.1 and MAVSDK

I installed px4 v1.9.1 release firmware on bebop2,and qgroundcontrol can connected it and worked correctly.but when I connect it with MAVSDK example(for example battery.cpp),it can discovered the drone but heartbeat message is timedout and the program aborted.
some tips about it?

yes I see,the MAV_PROTO_VER parameter set to 2(Always use version 2),then MAVSDK example connect the drone correctly and heartbeat message can be processed correctly.