This message was posted on behalf of Intel Corporation
Thanks for your interest in the Intel Aero drone.
The PX4 firmware is part of the Intel Aero image (.iso file), and you can also find the PX4 source directly from the PX4 repository, additionally, you can take a look at the PX4 Development Guide where you will find useful information to work inside the PX4 system architecture.
I’d like to recommend you to contact PX4 directly in case you need further information since they can provide you a more accurate answer, also I have found this PX4 forum that may help: http://discuss.px4.io/.
Hope you find this information useful.