PX4 firmware with Qgroundcontrol
download qgroundcontrol from here,http://qgroundcontrol.com/downloads/
After uploading firmware, You may experience a failure to connect to the ground station.That's because the parameters of chibios ardupilot conflict with nuttx of px4, you need to follow the steps below,
Hold safety switch during boot
Press and hold the safety switch while powering on the PixHawk. You should hear theupdating IO firmware soundthen boot should proceed.
More information you can read here,https://ardupilot.org/dev/docs/pixhawk-force-px4io-flash.html