How can i reach the control program in pixhawk?

I am working on my thesis about Pixhawk controller in Ubuntu. I installed PX4 toolchain and QtCreater and I am trying to reach the control program in Pixhawk for improvement. I calibrated all sensors and radio but couldn’t find the mean program doing all the system controller.
I can see programs in QtCreator coming from PX4 toolchain in src file but I’m not sure that programs which I’m searching for.
Can somebody help me with this? I must finish the school this term.

Here’s a brief overview of the architecture -

What specifically are you looking for?
multicopter attitude controller -
multicopter position controller -
state machine -
mission handling -

We’re happy to help point you in the right direction if you provide more detail.

I can see this codes in QtCreator. If i change the codes and upload the system, can i change the firmware in pixhawk?

Yes you definitely can!

If you make a account on, you can create a forked repository. That makes a separate copy of the firmware that you can modify.