Simple Functions Scheduler (SFS)

Description

A lightweight, cooperative task scheduler and free-run counter library for C. It is specifically designed for embedded systems and other environments where the C standard library is not available or desirable.

Key Features

• Zero Dependencies: Written in C89 (-ansi) and does not depend on any standard libraries.
• Deterministic Memory Usage: Uses a static memory pool for task management, avoiding malloc/free for predictable and stable long-term operation.
• Portable: Hardware-dependent operations (like interrupt control) are injectable via function pointers, making the core logic highly portable.
• Cooperative Scheduling: A simple, non-preemptive scheduler manages tasks based on a priority order.

Components

This library consists of five main components:

• SFS (Simple Functions Scheduler): The core scheduler. It manages the lifecycle of tasks (creation, dispatching, and termination).
• FRCC (Free Run Counter): A utility for timekeeping. It provides counter functionalities with overflow handling and support for atomic access, which is crucial for timer interrupts.
• FIFO (First-In, First-Out): A general-purpose FIFO queue with a fixed element size, designed for inter-task communication and event queuing.
• Ring Buffer: A flexible byte-stream ring buffer for handling continuous data streams, supporting custom read/write functions for hardware optimization (e.g., DMA).
• Matrix State Machine: A deterministic state management library using a 3D matrix (Mode x State x Event) for efficient and maintainable state transitions.

Requirements

• A C89-compliant C compiler (e.g., gcc).
• make for building the project.
• The pthreads library is required to build and run the sample programs, as they use it to simulate timer interrupts.

How to Build

Build the library and all sample programs by running make:

make

This command will compile and automatically run each sample program.

To clean up build artifacts, run:

make clean

The Makefile also includes targets for profiling (make gprof) and coverage analysis (make gcov).

Note on macOS Profiling: On macOS, make gprof uses the xctrace utility (part of Xcode) instead of gprof. It generates a .trace file that can be opened with Instruments.

Sample Programs

The sample programs demonstrate the key functionalities of the library.

• sample00.c: Demonstrates basic scheduling of two independent tasks using SFS_initialize, SFS_fork, and SFS_dispatch.
• sample01.c: Shows inter-task communication using the SFS_work and SFS_change functions.
• sample02.c: A task terminates itself from the schedule using SFS_kill.
• sample03.c: A "master" task controls the state of a "slave" task using SFS_otherWork.
• sample04.c: Demonstrates using the FIFO library for safe inter-task communication between a producer and a consumer.
• sample05.c: Verifies the Ring Buffer library functionalities, including basic read/write, overwrite mode, and dependency injection for custom data copy functions.
• sample06.c: Demonstrates the Matrix State Machine library, including state transitions across different modes and log callback injection.
• sample_frcc01.c: Demonstrates using the FRCC module for time-based task control. It uses the gFreeRunCounterMini variable as a time source and the GetFreeRunGapMini function to measure elapsed time.

Future Plans

• All initially planned features, including the Event Control Function (Matrix State Machine), have been successfully implemented.

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Attribution

This project was created with the assistance of CIP (Core-Intent Prompting Framework), a CC BY 4.0 licensed prompt framework for generative AI.