(Crazyflie 2.0 + PX4) Compass issue

Hi all,
I am integrating Crazyflie with PX4 as following https://docs.px4.io/en/flight_controller/crazyflie2.html and https://github.com/dennisss/cfbridge.

I have flashed PX4 firmware into CF2, and calibrated via QGC.

However, I got the error message that “warning: autopilot, internal mag with large offset”
Also I connected CF2 to computer through USB cable. (The other issue is that it did not communicate with Crazyradio PA T^T)
I checked compass has some trouble as you can see the following image.

Do you have any idea to resolve this issue?
I am using Ubuntu 14.04, QGC v3.2.4, PX4 is obtained from “https://github.com/PX4/Firmware

Thanks in advance.

It is because DC motors distorted the magnetic field around as they are very close to onboard mag. It is inevitable in such a micro size frame.
You can use LPE for indoor flight testing which ignores internal mag offset.

Or if you do need compass indoor then check this out:

NanoMind + nanoCompass

I am not expert on CF2 so better wait for @dennisss to answer these CF2 specific issues

In general, compass issue should not related to communication problem.

Vision based external camera array does not rely on compass to determine the heading of vehicle. But for a micro grade drone as its so small i doubt cameras can really tell the heading. You can still use gyro estimated heading as in LPE, however error will accumulate for longer time flight though in absence of external compass.