hermes: RC-Plane Flight Control System

Key Features

• Real-time flight control with FreeRTOS multitasking
• Wireless telemetry and remote control via nRF24L01
• Clean modular architecture with proper separation of concerns
• CMSIS-based implementation (no HAL dependencies)

Built for reliable autonomous and manual RC aircraft operation.

---

Project Architecture

System Overview

┌─────────────────┐    ┌──────────────────┐    ┌─────────────────┐
│   Applications  │    │    Controls      │    │    Devices      │
│                 │    │ - Sensors        │    │ - nRF24L01      │
└─────────────────┘    └──────────────────┘    └─────────────────┘
         │                       │                       │
         └───────────────────────┼───────────────────────┘
                                 │
┌─────────────────────────────────┼─────────────────────────────────┐
│                            Drivers                                 │
│  ┌─────────┐  ┌─────────┐  ┌─────────┐  ┌─────────┐              │
│  └─────────┘  └─────────┘  └─────────┘  └─────────┘              │
└─────────────────────────────────────────────────────────────────┘
         │
┌─────────────────────────────────┼─────────────────────────────────┐
│                            CMSIS                                   │
│                    STM32F103C8T6 Hardware                         │
└─────────────────────────────────────────────────────────────────┘

Task Architecture

Task Name	Responsibility	Priority	Communication
ControllerTask	Flight control logic, PID, stabilization	High	Processes sensor data

Communication Flow

                                                      ↑
                                                      ↑  
[ nRF24L01 (SPI) ] → [ Radio Handler ] ──────────────┘

---

Hardware Requirements

Component	Description	Interface
MCU	STM32F103C8T6 (Blue Pill) – Cortex-M3, 72 MHz, 20 KB RAM	-
Radio Module	nRF24L01+ for telemetry and remote control	SPI
Status LEDs	Debug and status indication	GPIO
Mode Button	Flight mode toggle	GPIO/INT
Power Source	Li-Po battery pack with voltage regulation	ADC

---

Getting Started

Prerequisites

Development Environment (Linux)

# Fedora/RHEL
sudo dnf install arm-none-eabi-gcc arm-none-eabi-newlib

# Ubuntu/Debian  
sudo apt install gcc-arm-none-eabi

# Verify installation
arm-none-eabi-gcc --version

Flashing Tools

# For ST-Link
sudo dnf install stlink  # or sudo apt install stlink-tools

# Alternative: OpenOCD
sudo dnf install openocd  # or sudo apt install openocd

Build and Flash

1. Clone the Repository

git clone https://github.com/msoodb/hermes.git
cd hermes

2. Build the Firmware

make clean
make

3. Flash to STM32

# Using ST-Link (default)
make flash

# Using OpenOCD
make METHOD=openocd flash

# Using GDB for debugging
make METHOD=gdb flash

Project Structure

hermes/
├── src/
│   ├── applications/     # Main application code
│   ├── board/           # Board initialization (clock, GPIO)
│   ├── controls/        # Flight control logic
│   ├── drivers/         # Low-level peripheral drivers
│   ├── system/          # System utilities, interrupts
│   └── utils/           # Utilities (debug, delay, fonts)
├── include/             # Header files
├── FreeRTOS/           # FreeRTOS source code
├── CMSIS/              # CMSIS and startup files
└── ld/                 # Linker scripts

---

Development Guidelines

Driver Architecture

• Controls: Application-level control logic (Flight controller, Sensor fusion)

Naming Convention

• All functions/types use hrms_ prefix
• Clear separation between drivers, devices, and controls
• Consistent error handling with status returns

Real-time Considerations

• Critical flight control tasks have high priority
• Sensor polling runs at medium priority
• Communication tasks at lower priority
• Proper use of FreeRTOS synchronization primitives

---

License

This project is licensed under the GNU General Public License v3. See the LICENSE file for details.

---

Built for reliable RC aircraft flight control and telemetry.