TaskScheduler — Tiny Cooperative Scheduler for Arduino

A lightweight, header-only task scheduler for small microcontrollers.
Implements simple RTOS-like primitives (tasks, priorities, delays, notifications, queues) — but runs entirely cooperatively, without interrupts or stack switching.

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✨ Features

• Header-only — just include TaskScheduler.h
• Cooperative — runs in loop(), no ISR or threading
• Prioritized tasks (vTaskPrioritySet, sorted run order)
• Delays & periodic execution (vTaskDelay, vTaskDelayUntil)
• Suspend/Resume support
• Task notifications (binary or counting semaphore style)
• Tiny fixed-size containers (no dynamic allocation)
• Wrap-safe timing using millis()
• Designed for small MCUs (AVR, ESP, etc.)

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🧩 Quick Example

#include <Arduino.h>
#include "TaskScheduler.h"

#define NUM_TASKS 2

TaskScheduler<NUM_TASKS> tm;

uint8_t hBlink;
uint8_t hMessage;

void blinkTask() {
  static bool on = false;
  digitalWrite(LED_BUILTIN, on);
  on = !on;
  tm.vTaskDelayUntil(500);
}

void messageTask() {
  Serial.println("Hello from TaskScheduler!");
  tm.vTaskDelayUntil(1000);
}

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.begin(115200);

  hBlink = tm.xTaskCreate(blinkTask, 0, 1);
  hMessage = tm.xTaskCreate(messageTask, 0, 2);
}

void loop() {
  tm.run();
}

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🧠 Example Collection

1️⃣ 01_Blink.ino

Minimal example: blink the onboard LED using a scheduled task.

2️⃣ 02_ResumeAfterBlink.ino

Demonstrates vTaskResumeAfter() to restart a paused task after a delay.

3️⃣ 03_SerialBlink.ino

Shows running two tasks: one blinking an LED and another printing serial messages with independent timing.

4️⃣ 04_SerialBlinkQueue.ino

Advanced example combining TaskScheduler with a TinyQueue to pass data between producer and consumer tasks.

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🛠️ How It Works

• Each task is a simple void() function.
• Tasks cooperatively yield back to the scheduler using one of:
  • vTaskDelay(ms) — schedule next run after ms
  • vTaskDelayUntil(period) — maintain a fixed periodic rate relative to the previous release time
  • vTaskYieldNextTick() — yield until the next scheduler tick (cheap throttle)
• The scheduler runs all tasks that are due, in priority order.
• If a task finishes without setting a next wake time → it is automatically suspended until resumed manually.

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📁 Included Headers

File	Description
TaskScheduler.h	Main cooperative scheduler (template-based)
Task.h	Task record + metadata
TaskMeta.h	Compact flags (in-use, enable, priority)
TaskKey.h	Packed task index/priority key
BoolArray32.h	Bitmask helper for up to 32 tasks
FixedQueue.h	Ring buffer FIFO (tiny queue)
FixedVector.h	Fixed-size container with sort
TaskQueue.h	Queue with built-in task wakeups
IScheduler.h	Interface base for queue callbacks

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⚙️ Configuration

TaskScheduler<NUM_TASKS> tm(quantumMs);

• NUM_TASKS: max number of tasks (≤ 32)
• quantumMs: tick quantum in milliseconds (default 1 ms)

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📜 License

MIT License © 2025 Tim Sonnenburg