computer science

RTEMS

RTEMS is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand RTEMS rather than just read about it. In short: Real-Time Executive for Multiprocessor Systems (RTEMS), formerly Real-Time Executive for Missile Systems, and then Real-Time Executive for Military Systems, is a real-time operating system (RTOS) designed for embedded systems. It is free and open-source software.

Key takeaways

RTEMS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect RTEMS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of RTEMS from memory before moving on to harder problems.

Reference excerpt

Real-Time Executive for Multiprocessor Systems (RTEMS), formerly Real-Time Executive for Missile Systems, and then Real-Time Executive for Military Systems, is a real-time operating system (RTOS) designed for embedded systems. It is free and open-source software. Development began in the late 1980s with early versions available via FTP as early as 1993. OAR Corporation managed the RTEMS project in cooperation with a steering committee until the early 2000s when project management evolved into a subset of the core developers managing the project. In 2014, hosting was moved from OAR Corporation to the Open Source Lab at Oregon State University.

Design RTEMS is designed for real-time embedded systems and to support various open application programming interface (API) standards including Portable Operating System Interface (POSIX) and μITRON (dropped in RTEMS 4.10). The API known as the Classic RTEMS API was originally based on the Real-Time Executive Interface Definition (RTEID) specification. RTEMS includes a port FreeBSD Internet protocol suite (TCP/IP stack) and support for various file systems including Network File System (NFS) and File Allocation Table (FAT). RTEMS provides extensive multi-processing and memory-management services.

Architectures RTEMS has been ported to various target processor architectures:

ARM AArch64 Atmel AVR Blackfin Freescale, now NXP ColdFire Texas Instruments – C3x/C4x DSPs Intel – x86 architecture members 80386, Pentium, and above LatticeMico32 Microblaze 68k MIPS Nios II OpenRISC PowerPC Renesas – H8/300, M32C, M32R, SuperH RISC-V RV32, RV64 using QEMU SPARC – ERC32, LEON, V9 V850

Uses RTEMS is used in many application domains. The Experimental Physics and Industrial Control System (EPICS) community includes multiple people who are active RTEMS submitters. RTEMS is also popular for space uses since it supports multiple microprocessors developed for use in space including SPARC ERC32 and LEON, MIPS, ColdFire, and PowerPC architectures, which are available in space hardened models. RTEMS is currently orbiting Mars as part of the Electra software radio on NASA's Mars Reconnaissance Orbiter, and the ESA's Trace Gas Orbiter., as well as passing by the sun on the Parker Solar Probe.

License RTEMS components are currently licensed under a mixture of licenses including a GPL-2.0 derived license with the project working on trying to re-license original components to the project under the two paragraph BSD license. RTEMS was originally distributed under a modified GNU General Public License (GPL), allowing linking RTEMS objects with other files without needing the full executable to be covered by the GPL. This license is based on the GNAT Modified General Public License with the language modified to not be specific to the programming language Ada.

Illustrations

Worked examples

Example 1 — a first encounter with RTEMS

Start with the simplest possible case. Write down what RTEMS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to RTEMS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about RTEMS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of RTEMS

In research: RTEMS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses RTEMS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: RTEMS is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1993 software, ARM operating systems, Embedded operating systems, so understanding it makes those chapters shorter.
In everyday life: Look for RTEMS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study RTEMS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what RTEMS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain RTEMS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RTEMS in simple terms?

Why does RTEMS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study RTEMS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on RTEMS.