Standards

2. Standards#

This chapter describes each of the standards which RTEMS tracks API alignment with. As a general rules, these standards are related to the POSIX or C programming language standards. Many are the result of domain specific efforts to define subsets or profiles or the full POSIX standard which are suitable for a specific domain. Each API set is considered a “profile” against which the full capability set of RTEMS is evaluated.

The RTEMS Complete Profile is the complete set of POSIX, BSD, and C programming language functions supported by RTEMS. This profile is independent of any standard and represents a union of multiple standards. For example, RTEMS supports BSD derived functions that are not in POSIX.

The IEEE Standard 1003.1 is the POSIX standard which is maintained by The Open Group. Specifically, IEEE Standard 1003.1-2003 is the 2003 edition of the POSIX standard which is referred to by The Open Group as Issue 6. IEEE Standard 1003.1-2008 is the 2003 Edition of the standard with two Technical Corrigenda applied. It does not have an issue number associated with it. IEEE Standard 1003.1-2017 is also known as Issue 7. Each edition of the POSIX standard tends to add some functions, deprecate some functions, and obsolete (e.g. remove) other functions.

API differences between Issue 5 and Issue 6 are documented at https://pubs.opengroup.org/onlinepubs/009695399/xrat/xsh_chap01.html. There is not a summary for the changes between Issue 6 as published and what was released as 1003.1-2008. However, there is a summary of API changes from Issue 6 to Issue 7 (POSIX 1003.1-2017) at https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap01.html.

Issue 8 was published in June 2024. The HTML version is not yet available on the web. It did include a list of newly added functions and deprecated functions.

PSE51 through PSE54 are Open Group defined profiles of the 2003 edition of the POSIX standard. These profiles are:

  • Profile 54 - Multipurpose

    • 1003.1-2003 Base Multi-process, Threads and File System

  • Profile 53 - Dedicated

    • Multi-process, Threads and File System

  • Profile 52 - Controller

    • Single Process, Threads, and File System

  • Profile 51 - Minimal

    • Single Process, Threads, with No File System

The C99 Programming Language standard defines the Standard C Library. This library is largely included by reference in the POSIX standard.

The C11 Programming Language standard defines also defines an updated version of the Standard C Library. It deletes a few functions from the C99 version but adds many functions. A large portion of these functions are optional and not commonly implemented.

Similarly, the C17 Programming Language standard defines an updated version of the Standard C Library.

The Open Group FACE Consortium (https://www.opengroup.org/face) has defined four POSIX profiles targetting the avionics application domain. The FACE Technical Standard has been through multiple revisions and the POSIX API profiles are identical in Editions 1.0, 2.0, 2.1, and 2.1.1. In these editions, the profiles and the approximate number of APIs in each are as follows:

  • Security - ~165 APIs, single process, no FILE *

  • Safety Basic - ~250 APIs, single process, some FILE *

  • Safety Extended - ~335 APIs, multi-process, more FILE *

  • General Purpose - ~825 APIs, multi-process, much more

FACE Technical Standard, Edition 3.0 adds the requirement for an operating system to support clock_nanosleep() in all profiles and defines one additional subcommand for the posix_devctl() functions.

FACE Technical Standard, Edition 3.1 has a number of minor changes to the profiles. Most of these were to improve alignment with the Software Communications Architecture (SCA) profiles. Additionally, some inconsistencies in the profiles were noticed and addressed while doing the alignment review.

FACE Technical Standard, Edition 3.2 has a few minor changes to the profiles.

RTEMS provides all of the functions required by the FACE Safety BASE profile and all of the functions in the Safety Extended profile which do not require multiple processes. Similarly, RTEMS provides nearly all of the functions in the General Purpose profile which do not require multiple processes. Support for the functions defined in fenv.h is processor architecture dependent.

The Software Communications Architecture (SCA) specification targets the requirements for software-defined radios. This specification was originally developed in support of the Joint Tactical Radio System (JTRS) program in conjunction with the Object Management Group (OMG). This standard is now maintained by the Wireless Innovation Forum with support from the U.S. Navy Joint Tactical Network Center (JTNC). Some URLs of interest:

The SCA standard is hosted at the Wireless Innovation Forum with JTNC hosting supplemental information.

RTEMS includes all functions required by the SCA POSIX profiles.