What is a Real-Time Operating System? | SUSE Communities

What is a Real-Time Operating System?


The world of computing is full of intricate systems designed to serve specific needs. One such specialized technology is the Real-Time Operating System (RTOS). Acting as a keystone of many high-demand applications, an RTOS facilitates tasks requiring precise, reliable, and efficient operations, keeping the wheels of our digital world spinning smoothly.

What is a Real-Time Operating System (RTOS)?

An RTOS is an operating system architected explicitly to manage resources, execute programs, and process data for real-time applications. What differentiates an RTOS from other operating systems is its primary focus: fast and predictable responses to events or data inputs.

Here, “real-time” means the system adheres to “real-time constraints” — or operational deadlines established from event inception to system response. These responses might need execution within seconds, milliseconds, or even microseconds, depending on the application’s demands.

While Linux, for instance, is a popular general-purpose operating system that shines with its feature set and user interface, it also showcases the duality of being used as an embedded or RTOS. This highlights the adaptability of some platforms to serve various needs, emphasizing the pivotal role they play in different applications.

RTOSs are indispensable in many critical applications, spanning the gamut from embedded systems in medical devices and aircraft navigation controls, to industrial processes, telecommunications and robotics.

Why use an RTOS?

The main feature of an RTOS is its predictability. With an RTOS, developers can ensure specific tasks are executed within a fixed timeframe. This feature is critical in systems where even minor delays can become critical, such as life support systems or air traffic control mechanisms, or when processes or threads need to be executed within a specific timeframe.

Furthermore, an RTOS offers robust control over system resources. It empowers developers to manage the allocation of processing power, ensuring critical tasks receive precedence over less vital ones. This function helps prevent system overloads or ‘bottlenecks’ that can slow down or crash the system.

Lastly, despite their specialized nature, most RTOSs are designed for compactness and efficiency, requiring less memory and power than many general-purpose operating systems. This quality makes them ideal for devices with resource constraints, such as embedded systems.

With this foundation in what an RTOS is and why it’s beneficial, we’ll further explore the types of RTOS, their requirements, how they function, and how SUSE can help with Linux-based RTOS implementations in the next sections.

Types of RTOS

We should understand that ‘Real-Time’ is not a monolithic concept; instead, there are three categories of Real-Time Operating Systems:

Hard Real-Time Operating Systems: These systems are designed for applications where missing a deadline is considered a system failure. For instance, in an anti-lock braking system, not responding to a sensor reading in time could be catastrophic.

Soft Real-Time Operating Systems: In these systems, missing a deadline is undesirable but not catastrophic. For instance, in a video streaming service, a delay in data processing might cause a temporary video glitch, but the system continues to function.

Firm Real-Time Operating Systems: These systems fall in between hard and soft RTOS. Here, missing a deadline is still considered a system failure, but it doesn’t have catastrophic consequences. For example, in automated factory systems, if a component is not in the right place at the right time, it may lead to production issues but not immediate dangerous consequences.

Linux, as an example, can be configured as a soft real-time operating system using its standard kernel or as a hard real-time operating system using patches such as PREEMPT_RT (Real-Time Patch).

RTOS requirements

To be considered Real Time, an operating system needs to meet a series of key requirements:

RTOS Requirement Explanation
Determinism Ensures operations happen within a strictly defined time frame.
Task Prioritization Prioritizes tasks based on their urgency and allocates CPU resources accordingly.
Concurrency Supports running multiple tasks at the same time or creating the appearance of simultaneity through multitasking.
Memory Management Efficiently allocates and deallocates memory segments without fragmentation, maximizing available memory at all times.
Minimal Latency Ensures the time taken to respond to an external event is minimal and consistent.
Reliability and Stability Highly necessary as many real-time systems are mission-critical.
Footprint Must have a small memory footprint due to frequent embedding in systems with constrained resources.

How does an RTOS work?

An RTOS achieves real-time behaviour through a combination of task scheduling, interrupt management, intertask communication and resource allocation. Let’s dig into the details:

Task Scheduling Interrupt Management Intertask Communication and Synchronization Resource Allocation
RTOS uses various scheduling algorithms, such as Rate Monotonic Scheduling or Earliest Deadline First, to decide which task should be executed at any given moment To ensure minimal response times, an RTOS must be able to quickly process interrupts and, if necessary, pre-empt an ongoing task to deal with the interrupt Tasks within an RTOS often need to communicate or synchronize with each other. RTOS provides mechanisms like semaphores, message queues, and event flags for this purpose The RTOS allocates resources such as CPU time, memory, and peripherals to different tasks according to their priority and needs

Why Linux is a perfect RTOS?

The open source nature of Linux provides the flexibility to shape the system to meet unique real-time demands. Implementing specific modifications, such as the PREEMPT_RT patch, can transform a standard Linux system into a high-performing real-time system.

Linux also offers unparalleled hardware support, extending from compact single-board computers like the Raspberry Pi to large-scale servers.

This adaptability allows for the effective deployment of Linux across diverse real-time applications, regardless of their complexity. Moreover, as a feature-rich platform supported by an extensive open community and trusted enterprise-level vendors, Linux is used and rigorously tested in a wide range of environments. As the most widely used operating system in the world, Linux is consistently improved and refined across all kinds of scenarios, which is an advantage hard to match by any other RTOS.

How SUSE can help

SUSE, known for its enterprise-grade Linux distributions, is well-poised to assist in implementing an RTOS solution.

SUSE Linux Enterprise Real Time is based on the latest real-time Linux kernel and includes the open source community’s latest real-time patch set—pre-empt RT—a set of patches that support pre-emption with adaptive locks, per device, interrupt threads and priority inheritance. It also includes support for CPU shielding, resource assignment, and high-resolution timers, as well as kernel drivers for the latest NVMe over Fabric and RDMA software stack.

In conclusion, a Real-Time Operating System is a critical component for many embedded and industrial systems. Understanding what an RTOS is, why we use them, their types, requirements and working principles can provide crucial insights into the digital world that powers our lives. With solutions like SUSE Linux Enterprise Real Time, we can leverage the adaptability and efficiency of RTOS to create reliable, responsive and robust applications with a leader in the Real Time and Embedded Enterprise Linux market.

Juan Herrera Utande
Juan Herrera Utande   Head of Technical Marketing