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 A real-time operating system (RTOS) is an operating system (OS) for real-time computing applications that processes data and events that have critically defined time constraints. A RTOS is distinct from a time-sharing operating system, such as Unix ...

(RTOS) designed for

embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...

s. It is

free and open-source software Free and open-source software (FOSS) is software available under a license that grants users the right to use, modify, and distribute the software modified or not to everyone free of charge. FOSS is an inclusive umbrella term encompassing free ...

. Development began in the late 1980s with early versions available via

File Transfer Protocol The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and d ...

(ftp) as early as 1993. OAR Corporation managed the RTEMS project in cooperation with a steering committee until the early 2000's when project management evolved into a subset of the core developers managing the project. In 2014, hosting was moved from OAR Corporation to the Oregon State Universit
Open Source Lab hosting

Design

RTEMS is designed for real-time embedded systems and to support various open application programming interface (

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

) standards including Portable Operating System Interface (

POSIX The Portable Operating System Interface (POSIX; ) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines application programming interfaces (APIs), along with comm ...

) and μITRON (dropped in RTEMS 4.10). The API now known as the Classic RTEMS API was originally based on the Real-Time Executive Interface Definition (RTEID) specification. RTEMS includes a

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manch ...

of the

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

(TCP/IP stack) and support for various file systems including

Network File System Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems (Sun) in 1984, allowing a user on a client computer to access files over a computer network much like local storage is accessed. NFS, like ...

(NFS) and

File Allocation Table File Allocation Table (FAT) is a file system developed for personal computers and was the default file system for the MS-DOS and Windows 9x operating systems. Originally developed in 1977 for use on floppy disks, it was adapted for use on Ha ...

(FAT). RTEMS provides extensive multi-processing and memory-management services.

Architectures

RTEMS has been ported to various target processor architectures: * ARM *

AArch64 AArch64, also known as ARM64, is a 64-bit version of the ARM architecture family, a widely used set of computer processor designs. It was introduced in 2011 with the ARMv8 architecture and later became part of the ARMv9 series. AArch64 allows ...

Atmel AVR AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. They are 8-bit RISC single-chip microcontrollers based on a modified Harvard architecture. AVR was one of the first microcontroller ...

Blackfin Blackfin is a family of 16-/32-bit microprocessors developed, manufactured and marketed by Analog Devices. The processors have built-in, fixed-point digital signal processor (DSP) functionality performed by 16-bit multiply–accumulates (MA ...

* Freescale, now NXP ColdFire *

Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...

– C3x/C4x DSPs * Intel –

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

architecture members

80386 The Intel 386, originally released as the 80386 and later renamed i386, is the third-generation x86 architecture microprocessor from Intel. It was the first 32-bit processor in the line, making it a significant evolution in the x86 architect ...

Pentium Pentium is a series of x86 architecture-compatible microprocessors produced by Intel from 1993 to 2023. The Pentium (original), original Pentium was Intel's fifth generation processor, succeeding the i486; Pentium was Intel's flagship proce ...

, and above * LatticeMico32 * Microblaze * 68k * MIPS *

Nios II Nios II is a 32-bit embedded processor architecture designed specifically for the Altera family of field-programmable gate array (FPGA) integrated circuits. Nios II incorporates many enhancements over the original Nios architecture, making ...

OpenRISC OpenRISC is a project to develop a series of open-source hardware based central processing units (CPUs) on established reduced instruction set computer (RISC) principles. It includes an instruction set architecture (ISA) using an open-source lic ...

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

* Renesas –

H8/300 The Hitachi H8 is a large family of 8-bit, 16-bit and 32-bit microcontrollers made by Renesas Technology, originating in the early 1990s within Hitachi Semiconductor. The original design, the H8/300, was an 8-bit processor that had a 16-bit ...

, M32C,

M32R The M32R is a 32-bit RISC instruction set architecture (ISA) developed by Mitsubishi Electric for embedded microprocessors and microcontrollers. The ISA is now owned by Renesas Electronics Corporation, and the company designs and fabricates M32R ...

SuperH SuperH (or SH) is a 32-bit reduced instruction set computing (RISC) instruction set architecture (ISA) developed by Hitachi and currently produced by Renesas. It is implemented by microcontrollers and microprocessors for embedded systems. At the ...

RISC-V RISC-V (pronounced "risk-five") is an open standard instruction set architecture (ISA) based on established reduced instruction set computer (RISC) principles. The project commenced in 2010 at the University of California, Berkeley. It transfer ...

RV32, RV64 using

QEMU The Quick Emulator (QEMU) is a free and open-source emulator that uses dynamic binary translation to emulate a computer's processor; that is, it translates the emulated binary codes to an equivalent binary format which is executed by the mach ...

* SPARC – ERC32, LEON, V9 * V850

Uses

RTEMS is used in many application domains. The Experimental Physics and Industrial Control System (

EPICS Epic commonly refers to: * Epic poetry, a long narrative poem celebrating heroic deeds and events significant to a culture or nation * Epic film, a genre of film defined by the spectacular presentation of human drama on a grandiose scale Epic(s) ...

) 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

architectures, which are available in space hardened models. RTEMS is currently orbiting Mars as part of the Electra software radio on

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Mars Reconnaissance Orbiter The ''Mars Reconnaissance Orbiter'' (''MRO'') is a spacecraft designed to search for the existence of water on Mars and provide support for missions to Mars, as part of NASA's Mars Exploration Program. It was launched from Cape Canaveral on Au ...

, and the ESA's

Trace Gas Orbiter The ExoMars Trace Gas Orbiter (TGO or ExoMars Orbiter) is a collaborative project between the European Space Agency (ESA) and the Russian Roscosmos agency that sent an atmospheric research orbiter and the ''Schiaparelli'' demonstration lande ...

., as well as passing by the sun on the

Parker Solar Probe The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a NASA space probe launched in 2018 to make observations of the Stellar corona, Sun's outer corona. It used repeated Gravity assist, gravity assists from ...

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 The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

(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.

References

External links