FreeRTOS with Dynamic EDF Scheduling for Event-Driven Systems

This repository contains a modified version of the FreeRTOS kernel that implements a low-overhead, dynamic Earliest Deadline First (EDF) scheduler. It is designed to improve performance and resource utilization in real-time embedded systems, particularly those with event-driven workloads.

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✨ Key Features

• ✅ Optimal Uniprocessor Scheduling: EDF is a proven optimal scheduling algorithm for uniprocessor systems. If a set of tasks can be scheduled by any algorithm, it can be scheduled by EDF.

• 🚀 Reduces Deadline Misses: In event-driven scenarios, this dynamic scheduler can reduce missed task deadlines by up to 60% compared to a standard static-priority scheduler.

• 💡 Low-Overhead Implementation: The scheduler is implemented with minimal overhead by using a single, deadline-sorted ready list. This results in up to 34.7% lower timing overhead and 74.7% lower memory overhead compared to the native FreeRTOS implementation.

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🚀 Getting Started

Prerequisites

• An ARM development environment (e.g., GCC for Arm, Keil, IAR).
• An existing FreeRTOS-based project.

1. Integration

To use the EDF scheduler, replace the standard FreeRTOS source files in your project with the files from the FreeRTOS/ directory of this repository.

2. Configuration

In your project's FreeRTOSConfig.h file, you must add the following definitions to enable and configure the dynamic scheduler:

/* Set to 1 to enable dynamic EDF scheduling.
 * Set to 0 to use the standard static priority scheduler. */
#define configDYNAMIC_SCHEDULING          1

/* Set to 1 to include the vTaskDeadlineRelSet() API function. */
#define INCLUDE_vTaskDeadlineRelSet       1

/* We recommend using the new scheduler with preemption and time slicing enabled. */
#define configUSE_PREEMPTION              1
#define configUSE_TIME_SLICING            1

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⚙️ API Reference

The core FreeRTOS API remains largely the same, with the following key additions and changes.

xTaskCreate()

The xTaskCreate() function is extended to accept a relative deadline as its final parameter.

BaseType_t xTaskCreate(
    TaskFunction_t       pvTaskCode,
    const char * const   pcName,
    configSTACK_DEPTH_TYPE usStackDepth,
    void * pvParameters,
    UBaseType_t          uxPriority,        /* Used only in static scheduling mode */
    TaskHandle_t * pxCreatedTask,
    TickType_t           xRelativeDeadline  /* New parameter for EDF! */
);

• xRelativeDeadline: Specifies the task's relative deadline in system ticks. This is the maximum time allowed from when the task becomes ready until it must complete its job.
• If configDYNAMIC_SCHEDULING is 1, the uxPriority parameter is ignored.
• If configDYNAMIC_SCHEDULING is 0, the xRelativeDeadline parameter is ignored, and the scheduler falls back to using uxPriority.

vTaskDeadlineRelSet()

If INCLUDE_vTaskDeadlineRelSet is enabled, you can dynamically change a task's relative deadline at runtime. This is useful for tasks whose urgency or execution requirements change.

void vTaskDeadlineRelSet(TaskHandle_t xTask, TickType_t xRelativeDeadline);

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📊 Usage Example

• The main.c file in this repository provides a clear example demonstrating the benefit of the dynamic EDF scheduler over a static, Deadline Monotonic (DM) scheduler.

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📜 Citation

If you use this work in your research, please cite the original paper. Link to the paper on IEEE Xplore:

@inproceedings{taji2023dynamic,
  title={Dynamic Scheduling for Event-Driven Embedded Industrial Applications},
  author={Taji, Hossein and Miranda, Jos{\'e} and Pe{\l}o{\'n}-Quir{\'o}s, Miguel and Balasi, Szabolcs and Atienza, David},
  booktitle={2023 IFIP/IEEE 31st International Conference on Very Large Scale Integration (VLSI-SoC)},
  pages={1--6},
  year={2023},
  organization={IEEE}
}

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⚖️ License

This project is licensed under the MIT License. See the LICENSE file for details.