I wired TTL-cable from J12 to laptop USB port and start ArduPilot below command:

sim_vehicle.py -v ArduCopter -A "--serial2=uart:/dev/ttyUSB0:921600"
(Also, 57600 and 115200).

Connection established with ArduCopter. But voxl-mavlink-server doesn't start. It gives 'PX4 DISCONNECTED FROM UART' error.

When I connect J12 to autopilot TELEM2 port and run voxl, voxl-mavlink-server runnig correctly.