RTOS Overview and Concepts

Overview

This lecture introduces real-time operating systems (RTOS), focusing on their differences from general-purpose operating systems, key concepts, use cases, and an upcoming practical series using FreeRTOS on ESP32 microcontrollers.

Operating Systems Overview

• Operating systems (OS) manage scheduling of background tasks and user applications, making concurrent execution appear seamless.
• OS manage virtual resources like files, folders, and libraries for application access.
• Device drivers in OS allow interaction with hardware like keyboards and displays.
• General-purpose OS (e.g., Windows, Linux, macOS) prioritize human interaction, tolerating small delays or lag.

Real-Time Operating Systems (RTOS) Features

• RTOS guarantee timing deadlines, making them suitable for time-critical applications like medical devices or engine controllers.
• RTOS may provide basic device drivers or just a scheduler, requiring custom drivers for additional hardware.
• RTOS allow reliable concurrent execution of multiple tasks, unlike simple super loop architectures.
• FreeRTOS is a popular, free, and open-source RTOS for IoT devices.

Super Loop vs. RTOS Approaches

• The super loop architecture uses a simple infinite loop to execute tasks sequentially—good for simple microcontroller projects with few tasks.
• Interrupts can handle precise timing or immediate response needs within both super loop and RTOS setups.
• Super loops struggle with concurrent tasks and can lead to missed input or lag if individual tasks take too long.

Tasks, Threads, and Processes

• A "task" (in FreeRTOS) is similar to a "thread"—a unit of code execution with its own context.
• Processes are program instances that may contain multiple threads and usually share resources.
• FreeRTOS generally runs a single process with multiple tasks (threads).

Prioritization and Multitasking

• RTOS allow task prioritization, ensuring urgent tasks get more CPU time or execute sooner.
• On single-core microcontrollers, multitasking is achieved by time-slicing CPU time between tasks.

When to Use RTOS

• RTOS are valuable for projects needing concurrent tasks, strict timing, or complex features like wireless connectivity.
• They are better suited for microcontrollers with ample memory and processing power (e.g., ESP32) rather than simple 8/16-bit MCUs.

Practical Information and Series Setup

• FreeRTOS is maintained by Amazon and works out-of-the-box on ESP32 boards (which come with Arduino support).
• Using Arduino provides a common environment for all learners and easy code portability.
• The series will include demo projects, challenges, and covers FreeRTOS fundamentals like task management and inter-task communication.

Key Terms & Definitions

• Operating System (OS) — Software managing hardware, resources, and task scheduling.
• Real-Time Operating System (RTOS) — OS guaranteeing timely task completion for critical applications.
• Super Loop — Simple program structure using a continuous infinite loop to process tasks sequentially.
• Task/Thread — An independent unit of code execution with its own program counter and memory.
• Process — An executing program instance, possibly containing multiple threads.
• Interrupt — A hardware- or software-triggered event that preempts running code to execute a service routine.

Action Items / Next Steps

• Prepare an ESP32 development board with Arduino support.
• Get ready to start using FreeRTOS by following the next video to create a task that blinks an LED.