RTOS vs Bare Metal: A Performance and Efficiency Showdown in Embedded Development

Welcome to <span>LiXin Embedded</span>.

In the business world, every choice made during development can determine the success or failure of a project. For instance, whether to use a Real-Time Operating System (RTOS) or to go with bare metal development is a headache-inducing decision. RTOS provides a structured development environment, fully functional and ready to use; whereas bare metal development interacts directly with the hardware, offering unparalleled control without any overhead from intermediary layers. The question arises: how do you choose what is best for your project? Today, we will discuss the performance, complexity, and efficiency of RTOS and bare metal development to help you clarify your thoughts and find the optimal solution.

What are the Differences Between RTOS and Bare Metal?

In simple terms, embedded systems can either choose to run with an operating system or go bare metal. Bare metal development means your code runs directly on the hardware, without intermediaries, requiring developers to handle hardware initialization, task scheduling, and everything else manually. This method is highly efficient, especially when optimized for specific tasks, with almost no overhead.

Conversely, RTOS acts like a smart housekeeper, managing hardware resources, scheduling tasks, and ensuring real-time performance. It allows multiple tasks to run “simultaneously” and provides inter-task communication, priority management, and scheduling features. For complex applications, RTOS can significantly simplify the development process and ensure real-time requirements are met.

In summary: bare metal development pursues ultimate efficiency and control, while RTOS offers structure and convenience, suitable for scenarios with strong real-time requirements or complexity.

Task Scheduling: Which is More Reliable?

Task scheduling is the core of embedded systems, directly affecting performance, especially in scenarios requiring real-time responses.

Bare Metal Development: In a bare metal environment, task scheduling is entirely up to the developer’s manual arrangement. There is no ready-made scheduler, typically implemented through a “Super Loop” or interrupt-driven approach. Critical tasks can be prioritized, leading to high efficiency. However, as system complexity increases, manual scheduling can become increasingly complicated, and a small oversight can lead to errors.

RTOS: RTOS comes with a built-in scheduler that automatically manages the execution order based on task priority. It supports preemptive or cooperative scheduling, ensuring high-priority tasks always run first, providing better guarantees for real-time performance. Developers do not need to worry about low-level details; they only need to define priorities, and RTOS will ensure everything runs smoothly.

In summary, bare metal scheduling is flexible but labor-intensive, while RTOS is automatic and reliable, especially suitable for complex or high real-time requirement scenarios.

Overhead: The Cost of Efficiency

Performance is the lifeblood of embedded systems, and overhead directly impacts efficiency. Let’s take a look at how the two compare.

Bare Metal Overhead: Bare metal has no operating system layer, and the code communicates directly with the hardware, resulting in almost zero overhead. Developers can meticulously optimize every operation, achieving maximum efficiency. However, this comes with risks: if the code is not well-written, or if system complexity increases, improper optimization can lead to uncontrollable overhead.

RTOS Overhead: As an intermediary layer, RTOS inherently brings some overhead, such as:

• Memory Usage: The kernel, task stacks, and data structures all require memory.
• Task Switching: Context switching consumes time and resources.
• API Calls: Calling system services is slower than direct hardware manipulation.
• Potential Latency: Complexity may lead to unpredictable delays.

However, these overheads are not without reason. The multitasking, communication mechanisms, and memory management features provided by RTOS make complex systems easier to scale and maintain. In other words, the overhead of RTOS is the “ticket” for functionality and maintainability.

Choosing between bare metal and RTOS depends on your project requirements. If it’s a simple application, the low overhead of bare metal is appealing; if it’s a complex system, the functionality gained from RTOS may be worth the overhead.

Code Maintenance

Embedded systems often need to run for many years, making code maintenance an unavoidable topic. How do RTOS and bare metal differ in maintainability?

Bare Metal Maintenance: Bare metal code runs directly on the hardware, giving developers complete control, and the code can be very concise. However, the challenges are significant:

• Poor Scalability: As the system becomes more complex, the code can easily turn into a tangled mess, making maintenance difficult.
• High Dependency: Changing one part may affect the entire system, and a small mistake can introduce bugs.
• Documentation Pressure: Without a standardized structure, documentation must be extremely detailed; otherwise, future developers will face a nightmare.

RTOS Maintenance: The structured design of RTOS makes maintenance easier:

• Modularity: Tasks are relatively independent, making development, testing, and maintenance clearer.
• Standard API: A unified interface makes the code more standardized, reducing maintenance costs.
• Tool Support: Many RTOS come with diagnostic tools and debuggers, making maintenance more efficient.
• Community Support: Popular RTOS have active communities, allowing quick answers to problems.

From a maintenance perspective, the modularity and standardization of RTOS are clearly more user-friendly, especially for long-term projects. While bare metal may be simpler initially, maintenance costs can skyrocket as the project grows.

Security Comparison

In the era of the Internet of Things, the security of embedded systems has shifted from being a “nice-to-have” to a “matter of life and death.” How do RTOS and bare metal perform in terms of security?

Bare Metal Security: The simplicity of the bare metal environment provides inherent advantages in security:

• Small Attack Surface: With no unnecessary components, there are fewer vulnerabilities.
• Complete Control: Developers can implement security measures precisely for the hardware.
• Predictable Behavior: Without operating system interference, verifying security properties is simpler.

However, the downside is that bare metal lacks built-in security features; all measures must be implemented by the developer, and any oversight can lead to significant issues. Moreover, as the system becomes more complex, security management can become exceptionally challenging.

RTOS Security: RTOS provides a wealth of security features:

• Memory Protection: Hardware-level memory isolation prevents task misoperations or malicious attacks.
• User/Kernel Mode: Sensitive operations are restricted, reducing vulnerability risks.
• Secure Boot: Supports verification of boot code to ensure only trusted programs run.
• Regular Updates: Popular RTOS continuously patch vulnerabilities to maintain security.

RTOS’s security features are more comprehensive, but they must be configured correctly. While bare metal is simple, security relies entirely on the developer, whereas RTOS provides standardized solutions suitable for high-security scenarios.

Real-Time Performance: Who is Faster?

For applications with high real-time requirements, such as medical devices and automotive systems, response speed is critical. How do RTOS and bare metal compare in real-time performance?

Bare Metal Real-Time Performance:

• Advantages:
• Direct Hardware Access: Code optimized for hardware leads to extremely fast response times.
• Strong Determinism: No operating system overhead, behavior is predictable.
• Low Latency: No context switching, operations have almost zero latency.
• Disadvantages:
• Complex Expansion: As tasks increase, manually ensuring real-time performance becomes challenging.
• Interrupt Management: Poor interrupt handling can introduce delays.

RTOS Real-Time Performance:

• Advantages:
• Preemptive Scheduling: High-priority tasks run first, ensuring real-time performance.
• Efficient Interrupt Handling: RTOS can manage interrupts efficiently, responding quickly.
• Timing Services: Provides precise timers to meet strict timing requirements.
• Disadvantages:
• Overhead: Context switching and other operations can introduce deterministic delays.
• Configuration Risks: Improper configuration may affect real-time performance.

For simple applications, bare metal can achieve extreme real-time performance, but in complex systems, the structured scheduling of RTOS is more reliable. When choosing, consider the real-time requirements and system complexity.

Cost: Which is More Economical?

Cost is always an unavoidable topic in embedded development. What are the cost differences between RTOS and bare metal?

Bare Metal Cost:

• Advantages:
• No Licensing Fees: No need to pay for an operating system.
• Hardware Optimization: Low overhead may allow for cheaper chips.
• Simple Tools: No need for expensive specialized development tools.
• Disadvantages:
• Time-Consuming Development: All functionalities must be written from scratch, leading to high labor costs.
• Expansion Costs: Future changes may require significant modifications, leading to soaring costs.

RTOS Cost:

• Disadvantages:
• Licensing Fees: Commercial RTOS may require payment.
• Hardware Requirements: Overhead may necessitate more powerful chips.
• Tool Costs: Specialized tools may be more expensive.
• Advantages:
• Development Efficiency: Existing functionalities speed up development, saving labor.
• Maintenance Ease: Modular design reduces long-term costs.
• Strong Scalability: Adapts to complex requirements, reducing the need for refactoring.

In the short term, bare metal is cheaper; in the long term, the development efficiency and maintainability of RTOS may save more money. It’s essential to consider the project cycle, team capabilities, and future needs when deciding.

Multitasking

Embedded systems often need to handle multiple tasks simultaneously, such as reading sensors, sending data, and controlling devices. How do RTOS and bare metal perform in multitasking?

Bare Metal Multitasking:

• Method: Achieved through interrupt-driven or simple polling.
• Advantages: Complete control over task order and timing, leading to high efficiency.
• Disadvantages:
• Task Blocking: Without preemption, low-priority tasks may get stuck.
• Complex Expansion: As tasks increase, manual management can easily lead to errors.

RTOS Multitasking:

• Method: Supports preemptive scheduling, task prioritization, and time slicing.
• Advantages:
• Efficient Scheduling: High-priority tasks run first and are not blocked.
• Communication Mechanisms: Semaphores, queues, etc., facilitate smoother task collaboration.
• Strong Scalability: Even with many tasks, everything remains orderly.
• Disadvantages:
• Overhead: Context switching consumes resources.
• Deadlock Risks: Improper resource management may lead to issues.

In multitasking scenarios, the structured management and communication mechanisms of RTOS are clearly more suitable for complex systems. Bare metal is suitable for simple scenarios, but as tasks increase, it can become unwieldy.

Development Complexity:

Development complexity directly affects project progress and quality. What are the differences in development experience between RTOS and bare metal?

Bare Metal Complexity:

• Advantages:
• Direct Control: Directly manipulating hardware allows for significant optimization.
• Simple Scenarios Friendly: Small projects are straightforward to develop.
• Predictable Behavior: No hidden background tasks.
• Disadvantages:
• Manual Management: All functionalities must be written by the developer, leading to potential errors.
• Expansion Difficulties: As the system becomes complex, management costs can skyrocket.

RTOS Complexity:

• Advantages:
• Ready-Made Features: Scheduling, communication, and other features are ready to use.
• Modularity: Code organization is clearer, and reusability is high.
• Community Support: Rich documentation and community resources.
• Disadvantages:
• Learning Curve: Newcomers may need time to adapt.
• Debugging Complexity: Interactions between multiple tasks may increase debugging difficulty.

For small projects, bare metal is simple and direct, but for large projects, the structured design of RTOS can save considerable effort. The choice depends on team experience and project complexity.

Power Consumption Comparison

In the era of IoT and portable devices, power consumption directly affects battery life. Who has the advantage in power consumption, RTOS or bare metal?

Bare Metal Power Consumption:

• Advantages:
• Code Optimization: Precise control over execution paths saves power.
• Direct Management: Quick switching to low-power modes.
• No Additional Overhead: No background tasks consuming power.
• Disadvantages:
• Manual Management: Power optimization relies entirely on the developer, leading to potential errors.

RTOS Power Consumption:

• Advantages:
• Advanced Management: Supports efficient switching to low-power modes.
• Scheduling Optimization: Tasks run only when needed.
• Waking Mechanism: Precise management of wake events.
• Disadvantages:
• Overhead: Context switching and system tasks consume power.
• Limited Control: The abstraction layer may limit extreme optimization.

In terms of power consumption, bare metal is suitable for extreme optimization in simple scenarios, while RTOS is better for complex systems requiring systematic power management. The key is to consider your device’s power consumption needs and optimization capabilities.

Conclusion: How to Choose?

The choice between RTOS and bare metal development is essentially a trade-off between control, efficiency, and complexity. Bare metal development is like a runaway horse, highly efficient and offering strong control, suitable for simple, power-sensitive scenarios; RTOS, on the other hand, is like a well-equipped ship, clearly structured and powerful, capable of easily handling complex, real-time demands.

When making a choice, ask yourself a few questions:

• Is the project complex? Does it require multitasking or real-time performance?
• Which development method is the team familiar with?
• Will there be a need for future expansion or maintenance?
• Are power consumption and cost constraints strict?

For simple projects, bare metal may be more straightforward; for complex systems, RTOS is almost a standard. Ultimately, the choice should reflect the core requirements and long-term goals of the project, finding the balance that best suits your needs.