RTEMS
RTEMS (Real-Time Executive for Multiprocessor Systems) è un sistema operativo di tipo real-time operating systemdistribuito in modalità open source real-time operating system e progettato per sistemi embedded systems.
L' acronimo RTEMS deriva inizialmente dal nome del progetto, Real-Time Executive for Missile Systems, che poi fu trasformato in Real-Time Executive for Military Systems e quindi nel più pacifico Real-Time Executive for Multiprocessor Systems. Lo sviluppo dell' RTEMS inizio' verso la fine degli anni 80 del secolo scorso, mentre le prime versioni disponibili, scaricabili tramite ftp, risalgono al 1993. RTEM viene gestito dalla società OAR Corporation, in cooperazione con un comitato di coordinamento che include una rappresentanza degli utenti di questo sistema.
RTEMS è stato portato su molte architetture e CPU, tra cui:
- ARM
- Blackfin
- ColdFire
- Texas Instruments C3x/C4x DSPs
- H8/300
- i386, Pentium, e i membri della famiglia X86
- 68K
- MIPS
- Nios_II
- PowerPC
- SuperH
- SPARC
Una particolarità di RTEMS, rispetto a altri sistemi operativi, è il supporto a molte API standard,incluso le API POSIX e le API ITRON del progetto TRON. Le API native di RTEMS sono ora denonimate "Classic RTEMS API" e furono originariamente basate sulle specifiche RTEID, acronimo di Real-Time Interface Executive Definition. RTEMS include lo stack TCP/IP derivato da FreeBSD e supporta molti filesystems, tra cui NFS e il FAT filesystem.
RTEMS does not provide any form of memory management or processes. In POSIX terminology, it implements a single process, multithreaded environment. This is reflected in the fact that RTEMS provides nearly all POSIX services other than those which are related to memory mapping, process forking, or shared memory. RTEMS closely correponds to POSIX Profile 52 which is "single process, threads, filesystem" (see http://www.linuxdevices.com/news/NS3992179355.html).
RTEMS is used in many application domains. The EPICS community includes multiple persons 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 Mongoose-V, Coldfire, and PowerPC architectures, which are available in space hardened models. RTEMS is currently circling Mars as part of the Electra software radio (see Mars Reconnaissance Orbiter).
RTEMS is distributed under a modified GPL licence, allowing linking RTEMS objects with other files without requiring 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 Ada programming language.