NibbleOS 🚀

A complete Real-Time Operating System that fits in a nibble of memory!

NibbleOS is an ultra-lightweight RTOS designed for Arduino boards with limited resources. It provides professional multitasking capabilities, inter-task communication, and power management - all in a single .ino file under 4KB.

✨ Features

• 🎯 Single File - No libraries to install, just copy and upload
• 🚀 Tiny Footprint - Under 4KB flash, ~200 bytes RAM
• ⚡ Preemptive Multitasking - Up to 6 concurrent tasks with priorities
• 🔒 Synchronization - Semaphores and events for task coordination
• 💬 Message Passing - Inter-task communication with 8-byte messages
• 🔋 Power Management - Built-in low-power modes for battery operation
• 🖥️ Interactive Shell - Debug and control via Serial Monitor
• 🛡️ Watchdog Support - Automatic system recovery
• ⏱️ Real-time - 100Hz scheduler with predictable timing

🚀 Quick Start

1. Download NibbleOS.ino
2. Open in Arduino IDE
3. Upload to your board (Uno, Nano, Pro Mini, etc.)
4. Open Serial Monitor at 115200 baud
5. Type help to explore!

// Your first NibbleOS task
void myTask() {
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
}

void setup() {
    os.createTask(myTask, 500, OS_PRIORITY_NORMAL, "Blinker");
    os.run();  // Start the RTOS
}

💻 Interactive Shell

Connect via Serial Monitor (115200 baud) for real-time system control:

NibbleOS v1.0
Ultra-light RTOS
Type 'help' for commands

> tasks
0: Shell [RUN] Pri:3 Last:45823
1: LED [READY] Pri:1 Last:45500  
2: Monitor [READY] Pri:1 Last:40000
3: WDog [READY] Pri:3 Last:45000

> mem
Free: 1823 bytes
Uptime: 46 sec
Context switches: 1247

> led 1
OK

Available Commands

Command	Description	Example
help	Show all commands	help
tasks	List all tasks with status	tasks
mem	Memory and system stats	mem
led <n>	Control built-in LED	led 1
adc <pin>	Read analog pin	adc A0
gpio <pin> <val>	Set digital pin	gpio 7 1
suspend <id>	Suspend a task	suspend 2
resume <id>	Resume a task	resume 2
power <0|1>	Set power mode	power 1

📊 Resource Usage

Board	Flash	RAM	Status
Arduino Uno/Nano	~3.5KB (11%)	~200B (10%)	✅ Excellent
Pro Mini	~3.5KB (11%)	~200B (10%)	✅ Excellent
Leonardo	~3.5KB (12%)	~200B (8%)	✅ Excellent
Mega 2560	~3.5KB (1%)	~200B (2%)	✅ Excellent
ATtiny85	~3.5KB (43%)	~200B (39%)	⚠️ Tight fit

🔧 Core API

Task Management

// Create a task
int taskId = os.createTask(function, periodMs, priority, "name");

// Task control
os.sleepTask(milliseconds);     // Sleep current task
os.suspendTask(taskId);          // Suspend a task
os.resumeTask(taskId);           // Resume a task

Synchronization

// Semaphores
int sem = os.createSemaphore(initialCount, "name");
os.waitSemaphore(sem, timeoutMs);
os.signalSemaphore(sem);

// Events  
int evt = os.createEvent("name");
os.waitEvent(evt, timeoutMs);
os.triggerEvent(evt);

Communication

// Send message to another task
uint8_t data[] = {1, 2, 3};
os.sendMessage(taskId, msgType, data, sizeof(data));

// Receive message
uint8_t buffer[8];
uint8_t type;
int size = os.receiveMessage(&type, buffer, sizeof(buffer));

🎯 Example Applications

Sensor Monitor with Alarm

int alarmEvent;

void sensorTask() {
    int value = analogRead(A0);
    if (value > 700) {
        os.triggerEvent(alarmEvent);
    }
}

void alarmTask() {
    os.waitEvent(alarmEvent, 0);  // Wait forever
    digitalWrite(BUZZER_PIN, HIGH);
    os.sleepTask(1000);
    digitalWrite(BUZZER_PIN, LOW);
}

void setup() {
    alarmEvent = os.createEvent("Alarm");
    os.createTask(sensorTask, 100, OS_PRIORITY_HIGH, "Sensor");
    os.createTask(alarmTask, 0, OS_PRIORITY_NORMAL, "Alarm");
    os.run();
}

Producer-Consumer Pattern

int dataSem;

void producer() {
    // Produce data...
    os.signalSemaphore(dataSem);
}

void consumer() {
    os.waitSemaphore(dataSem, 0);
    // Process data...
}

🔋 Power Optimization

NibbleOS includes built-in power management:

// Enable low power mode
os.setLowPowerMode(true);

// Task automatically sleeps when idle
void efficientTask() {
    // Do work...
    os.sleepTask(5000);  // Sleep 5 seconds
}

🛠️ Configuration

Edit these defines in NibbleOS.ino to customize:

#define OS_MAX_TASKS 6              // Maximum concurrent tasks
#define OS_SCHEDULER_FREQ_HZ 100    // Scheduler frequency
#define OS_TASK_MAX_RUNTIME_MS 2000 // Max task runtime
#define ENABLE_WATCHDOG             // Enable/disable features
#define ENABLE_MESSAGING
#define ENABLE_POWER_MANAGEMENT

📈 Performance

• Context Switch: ~50μs on 16MHz ATmega328
• Scheduler Overhead: <2% CPU @ 100Hz
• Message Passing: ~10μs per message
• Semaphore Operations: ~5μs

🤝 Contributing

Contributions are welcome! Feel free to:

• Report bugs
• Suggest features
• Submit pull requests
• Share your projects

📄 License

MIT License - see LICENSE file for details.

🌟 Why NibbleOS?

• Educational: Learn RTOS concepts with readable code
• Practical: Production-ready for small projects
• Efficient: Minimal overhead, maximum features
• Simple: One file, zero dependencies

🚧 Roadmap

• Task statistics collection
• Priority inheritance for semaphores
• Dynamic task creation/deletion
• Software timers
• Queue support
• ESP8266/ESP32 port

💡 Tips

1. Start Simple: Begin with basic tasks before adding synchronization
2. Watch Stack: Each task uses stack space, monitor with mem command
3. Use Priorities: Critical tasks should have higher priority
4. Avoid Blocking: Use events/semaphores instead of busy waiting
5. Test Limits: Use shell to suspend/resume tasks during development

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Made with ❤️ for the Arduino community
⭐ Star this project if you find it useful!