Frequently Asked Questions

FRESCOR.org is an independent knowledge resource about real-time embedded systems, relaunched in 2026. We publish in-depth articles on scheduling, timing analysis, RTOS platforms, embedded architectures and real-time networking, along with free tools such as the schedulability calculator and a glossary. The site also keeps a factual archive of the original FRESCOR research project. You can read more about our mission and principles on the About Us page.

No. This site is not operated by, affiliated with or endorsed by the original FRESCOR consortium, any of its partner organizations, or the European Commission. The FRESCOR project ran from 2006 to 2009 under the EU Sixth Framework Programme and was coordinated by the Universidad de Cantabria. We describe it for historical and educational purposes on pages such as the project overview and partners, written from publicly available information.

The FRESCOR project (FP6/2005/IST/5-034026) aimed to integrate contract-based flexible scheduling into component-based design for embedded systems. Components declare their resource and timing needs as contracts, and a framework guarantees them while distributing spare capacity. Its results were to be evaluated in multimedia phone video streaming, software-defined radio and digital video surveillance. See the objectives and expected results pages for more.

Our content is produced by the team behind FRESCOR.org, with a focus on real-time and embedded engineering. Technical claims are checked against primary sources such as textbooks, standards, official documentation and peer-reviewed literature, and every article lists its references. We do not invent statistics, quotes or testimonials. Our full approach to sourcing, corrections and independence is described in the editorial policy.

Please use the contact page or e-mail support@frescor.org. For corrections, include the page address, the passage in question and, ideally, a reference that supports the fix. We review every report and update the article and its “last updated” date when a correction is needed. Topic suggestions are very welcome, especially questions you have not found answered clearly elsewhere.

A real-time system is one whose correctness depends not only on the result it produces but also on when it produces it. Each task has timing constraints, usually expressed as deadlines. Real-time does not mean “fast”; it means predictable. A slow system that always meets its deadlines is real-time, while a fast one that occasionally misses them may not be. Our article What Is a Real-Time Embedded System? explains the idea in depth.

Missing a hard deadline is considered a system failure, potentially with safety consequences, as in airbag deployment or flight control. A result delivered after a firm deadline is useless and discarded, but occasional misses are tolerable, as with a dropped video frame. With a soft deadline, a late result still has some value that decreases with lateness. These categories determine which analysis and scheduling techniques are appropriate. See the glossary for related terms.

Rate Monotonic (RM) assigns fixed priorities by period and is supported by virtually every RTOS; its behavior under overload is predictable for high-priority tasks. Earliest Deadline First (EDF) uses dynamic priorities and can schedule any task set with utilization up to 100% on a single processor under the classic model, but needs more runtime support. Our practical comparison walks through the trade-offs with examples.

The worst-case execution time (WCET) is the longest time a piece of code can take to execute on a given platform, considering all inputs and hardware states. It is hard to determine because modern processors use caches, pipelines, branch prediction and shared buses whose behavior depends on execution history. Testing alone rarely triggers the true worst case. Static, measurement-based and hybrid methods each address this differently, as explained in our WCET analysis methods article.

Contract-based scheduling lets each software component state its requirements, such as a minimum processor budget per period and a deadline, as a contract. The scheduler admits the contract only if it can be guaranteed alongside existing ones, then enforces it through resource reservations so components cannot interfere with each other. Spare capacity can be shared according to importance. Read Contract-Based Scheduling Explained for the full picture.

The schedulability calculator takes a set of periodic tasks, each with an execution time, period and optional deadline, and checks it under Rate Monotonic and Earliest Deadline First scheduling. It reports total utilization, compares it against the Liu and Layland bound, performs exact response-time analysis for fixed priorities and draws a Gantt chart of the schedule. It is designed to perform its calculations in your browser, and it is free to use without an account.

The calculator is an educational and sanity-checking tool. It uses the classic independent periodic task model on a single processor and does not account for blocking, release jitter, interrupts, cache effects or multicore interference unless stated. Its results are only as good as the execution times you enter. For production or certified systems, use qualified analysis tools and processes. Our disclaimer explains this, and our schedulability audit offers a more thorough review.

Begin with What Is a Real-Time Embedded System? for the core vocabulary. Then read Rate Monotonic vs Earliest Deadline First and work through the response-time analysis example, trying the task sets in the calculator. After that, priority inversion and choosing an RTOS connect the theory to real platforms.

We review articles when relevant standards, kernel features or RTOS releases change, and whenever a reader reports an error. Each article shows a “last updated” date so you can judge how current it is. Fast-moving topics, such as RTOS comparisons and Linux scheduling features, are revisited more often than foundational theory. The blog lists all articles, and the site map shows every page.

Linking to any page on the site is always welcome. Short quotations with attribution and a link back to the original article are fine for commentary, teaching and research. Republishing full articles or substantial portions requires our prior written permission. Details are in our terms and conditions. If you believe content on our site infringes your rights, please follow the process in our DMCA policy.

FRESCOR.org offers a schedulability audit, RTOS selection and migration consulting, a WCET and timing analysis service, real-time Linux tuning with PREEMPT_RT and SCHED_DEADLINE, a contract-based scheduling training workshop, and a downloadable eBook, The Embedded Timing Field Guide. Each is described on the services page with its scope, deliverables and typical timeline. Our services are kept separate from editorial content, as explained in our editorial policy.

After you place an order on the services page, we contact you to schedule a kick-off call. During that call we review your system, goals and constraints and confirm the scope. The final scope, deliverables and timeline are then set out in a written statement of work before any substantive work begins. If you are unsure which service fits your needs, contact us first and we will help you choose.

Refund terms depend on the type of purchase. Consulting services and workshops can generally be cancelled before work starts or before the scheduled session, subject to the conditions in our policy. Downloadable products such as the eBook are treated differently once the file has been accessed, in line with applicable consumer law. Please read our refund policy for the full conditions, and contact support@frescor.org with your order details if you need help.

Yes. Source code, designs, timing data and other material you share during an engagement are used only to deliver the agreed service and are not published or shared with third parties. If you need a mutual non-disclosure agreement before sending sensitive material, raise it when you first contact us. How we handle personal data more generally is described in our privacy policy, and the specific confidentiality terms of an engagement are confirmed in its statement of work.

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