A Real-Time Management System for Flight Simulation Based on VxWorks
Abstract #
Based on a large-scale engineering flight simulator developed by the Department of Automatic Control at Beihang University (Beijing University of Aeronautics and Astronautics), this paper presents the architecture and implementation of a real-time management system built on the VxWorks embedded real-time operating system and a multiprocessor platform. The characteristics of VxWorks are first analyzed, followed by a description of the overall structure of the flight simulation system and the core functions of the management subsystem. Key implementation techniques are then discussed, with emphasis on multitask management across different development environments and real-time data communication in distributed simulation systems.
1. Introduction #
Engineering flight simulation systems are essential tools for aircraft research, design validation, and performance evaluation. At the core of such systems lies the real-time management system, which coordinates and controls all simulator subsystems, including the simulation computers, instructor console, visual system, motion system, instruments, and audio components.
The real-time management system functions as the “central nervous system” of the simulator. It is responsible for task scheduling, subsystem activation, real-time data coordination, monitoring, and fault handling, ensuring that the simulator operates in a safe, stable, and highly realistic manner. Additionally, it provides graphical human–machine interfaces (HMIs) and debugging environments to support simulation control and analysis.
Due to strict real-time constraints and computational complexity, engineering flight simulators are typically implemented using distributed multiprocessor systems. Leveraging the performance of modern 32-bit (and beyond) processors requires a reliable, efficient, and scalable real-time operating system. VxWorks, developed by Wind River Systems, is widely adopted in aerospace and defense applications for precisely these reasons. This paper describes the successful application of VxWorks in the development of a real-time management system for an engineering flight simulator.
2. Characteristics of VxWorks #
Real-time operating systems are commonly classified as soft real-time or hard real-time, depending on their ability to guarantee response deadlines. VxWorks is a hard real-time operating system, offering deterministic response times at the microsecond level.
Key characteristics that make VxWorks suitable for flight simulation systems include:
- Microkernel architecture: The VxWorks kernel is compact (as small as several kilobytes) and modular, allowing developers to include only required components. This reduces system complexity and improves reliability.
- Deterministic multitasking: VxWorks uses priority-based preemptive scheduling with optional round-robin scheduling for tasks of equal priority, ensuring predictable task execution.
- High reliability: Designed for mission-critical environments, VxWorks is widely used in aerospace, military, and industrial control systems.
- Multiprocessor support: VxWorks supports symmetric and asymmetric multiprocessor configurations, providing mechanisms for inter-processor communication and synchronization.
- Rich IPC mechanisms: Semaphores, message queues, shared memory, and events enable efficient coordination between tasks and processors.
- Integrated development environment: The Tornado IDE provides cross-compilation, debugging, simulation (VxSim), and performance analysis tools such as WindView.
These features make VxWorks an effective foundation for complex, real-time flight simulation platforms.
3. Overall Structure of the Flight Simulation System #
The flight simulation system consists of multiple subsystems, including:
- Simulation computer system
- Instructor operating station
- Visual display system
- Motion platform
- Instrument and control panels
- Audio and environmental systems
Among these, the simulation computer system is the core component. It executes real-time mathematical models such as flight dynamics, engine behavior, avionics logic, and control laws, and distributes simulation data to other subsystems.
The system adopts a distributed multiprocessor architecture based on a VME bus. Multiple CPUs are assigned dedicated simulation responsibilities, such as flight control, hydraulics, and landing gear simulation. A dedicated management CPU, running VxWorks, is responsible for global coordination, task scheduling, and data management.
To meet strict real-time communication requirements, the system employs a reflective memory network, enabling low-latency, deterministic data sharing across processors.
4. Main Functions of the Management System #
The real-time management system provides the following core functions:
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System initialization Loading simulation models, configuring initial parameters, and activating subsystems.
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Real-time scheduling Managing multiple real-time tasks and ensuring that simulation frame deadlines (e.g., 20 ms per frame) are consistently met.
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Data management Handling real-time input/output data, recording flight parameters, and supporting playback and analysis.
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Monitoring and debugging Providing graphical interfaces for system monitoring, parameter adjustment, fault injection, and runtime diagnostics.
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Communication control Coordinating data exchange among subsystems using shared memory, reflective memory, and network communication.
The system includes a graphical user interface based on technologies such as X Window System or Motif, enabling intuitive interaction for operators and engineers.
5. Key Implementation Techniques #
5.1 Multitask Management Across Development Environments #
In the Tornado host development environment, multitask management is implemented using standard VxWorks APIs such as taskSpawn, taskSuspend, and taskDelete. In the target environment, additional considerations include:
- Task priority assignment to ensure real-time deadlines
- Stack size configuration to prevent overflow
- Memory allocation strategies suitable for real-time execution
- Deadlock and priority inversion prevention
Performance analysis tools such as WindView are used to visualize task execution, context switching, and CPU utilization. In multiprocessor configurations, task-to-CPU affinity is configured to improve determinism and performance. Exception handling mechanisms are also implemented to ensure graceful recovery from runtime errors.
5.2 Real-Time Data Communication in Distributed Simulation Systems #
For high-speed and deterministic data sharing, the system uses reflective memory cards (e.g., VMIC-5576). Data written to local memory is automatically replicated across all participating nodes with minimal latency, making it well suited for tightly coupled simulation tasks.
For non-real-time or supervisory communication, Ethernet and TCP/IP are used. Synchronization between processors is achieved using interrupts triggered by reflective memory updates.
To minimize communication latency and jitter:
- Data structures are carefully aligned and optimized
- Redundant memory copies are avoided
- Communication cycles are synchronized with the simulation frame rate
6. Conclusion #
The VxWorks-based real-time management system described in this paper successfully satisfies the stringent real-time and reliability requirements of an engineering flight simulator. By leveraging VxWorks’ deterministic scheduling, multiprocessor support, and efficient inter-process communication mechanisms, the system achieves stable multitask execution and low-latency data exchange in a distributed environment.
The design and implementation approach presented here provides a practical reference for the development of similar real-time simulation and training systems in aerospace and other mission-critical domains.