Purpose of STM32F103 on Cube (Pixhawk 2)

[EyalAlon]

We intend to develop custom firmware for the Cube (Pixhawk 2).

We have reviewed related documentation and posts such as:
https://docs.px4.io/en/flight_controller/pixhawk-2.html

How to edit PX4 firmware and used it for our purpose?

Hi There, The reason for me to put this post is that recently I have been using Pixhawk 4 controller with PX4 firmware to build something new. I am working on creating Quadruped Robot (4-Legged Robot). I think PX4 firmware as well the Pixhawk controller play a vital role. As I just need to understand the PX4 code and edit a little bit and made it ready for the quadruped robot. But I am having a trouble to understand that where should I start. The main sensor I need for that is IMU, Force sensor…

https://dev.px4.io/en/concept/architecture.html

Despite reviewing the posts above, we have not been able to understand the intended purpose of the STM32F103 within the context of the PX4 cube system. Furthermore, how does the STM32F103 and STM32F427 communicate? Additionally, which firmware and how is it uploaded to the STM32F103?