one of the processes running on-board is called autel_simulink. Looking at simulink as it applies to PX4, I found that flight models can be developed using Simulink sofware, and subsequently uploaded to the Pixhawk. This would seem to indicate that Autel Robotics uses this tool for FMU development.
Pixhawk PX4 Support from Embedded Coder
PX4 Development Kit for Simulink
Pixhawk PX4 Support from Embedded Coder
PX4 Development Kit for Simulink
