200 MPH Drone RTOS

200 MPH Drone Real-Time Operating System (RTOS)

The 200-MPH Drone RTOS project aims to develop a high-speed drone capable of reaching velocities up to 200 mph by creating a custom, ground-up Real-Time Operating System (RTOS). This initiative focuses on the software component, emphasizing the scheduling of processes and the execution of PID loops with minimal latency to ensure precise flight control.

Project Overview

Achieving safe and reliable control of a quadcopter at such extreme speeds requires advanced computational handling. This project overcomes the limitations of conventional cooperative loop structures, where a delayed calculation or blocked process can result in significant control errors. The repository features a hybrid RTOS designed specifically for the STM32F7 (ARM Cortex-M7) microcontroller, addressing the need for ultra-low latency and deterministic flight operations.

Custom RTOS Architecture

Given the exigencies of flight stabilization at 200 MPH, the hybrid RTOS separates task execution into two functional zones:

1. The Scheduled Zone (Cooperative): Handles low-to-medium priority tasks such as battery telemetry and on-screen display (OSD) updates, executed sequentially.
2. The Interrupt Zone (Preemptive): Processes high-priority tasks, including IMU sensor readings and critical RC radio packet parsing, which preempt the standard queue for immediate execution. This is accomplished using the ARM Cortex-M7 PendSV exception vector to ensure fast, deterministic task switching.

Technical Achievements

• Asynchronous Context Saving/Restoring: Optimized in assembly to preserve the complete set of CPU registers during preemptive swaps, preventing task loss and memory corruption.
• C++ Parameter Overloading: Developed streamlined task creation functions to clearly delineate between scheduled and interrupt tasks, enhancing code maintainability.
• Low-Level Hardware Drivers: Established non-blocking SPI and UART drivers for efficient data handling from IMU sensors and telemetry packets.

Interactive Simulation Demo

An interactive simulation environment powered by Renode allows users to observe the kernel's preemption capabilities in real-time on a virtual STM32F7 setup. The simulation features:

• Continuously incremented counters from a low-priority background task.
• Random triggers for high-priority interrupts simulating real-world hardware events.

Repository Structure

• /src/flight: Contains core flight control application code, including IMU processing and CRSF radio packet handling.
• /src/rtos: Houses the custom RTOS kernel, including task control and scheduling mechanisms.

Project Roadmap

Phase	Name	Description	Status
#1	Custom RTOS Kernel	Execution of preemptive and cooperative tasks under a priority-based system	Complete
#2	Flight Dynamics	Implementation of low-pass filtering and state machine for OSD warnings	Complete
#3	Controller Loops	Development of high-rate PID controller loops and DShot signal generation	Complete
#4	Hardware Integration	Completion of Software-In-Loop (SIL) simulations for ESC and transmitter modules	Complete
#5	User Features	Implementation of CLI config tools, CPP bootloader, and USBC integration for testing	Complete

Future Goals

The aim is to complete the entire system integration by late August, following collaboration with hardware development to finalize the drone's build. Significant milestones are anticipated around mid-November, focusing on debugging and merging firmware components to ensure comprehensive readiness for flight operations.