This document specifies both the interface and the behavior of the API services. Behavior is specified to the extent needed to describe functionality relevant to calling applications.

Where necessary, assumptions are made as to the support or behavior provided by the operating system and hardware. This should not be construed as a specification for the O/S or hardware. However, where the O/S or hardware does not coincide with the stated assumptions, the API behaviors specified herein may not match the actual behavior.

ARINC 653 is intended for use in a partitioned environment. In order to assure a high degree of portability, aspects of the partitioned environment are discussed and assumed. However, this specification does not define the complete system, hardware, and software requirements for partitioning nor does it provide guidance on proper implementation of partitioning, and in particular, robust partitioning. It must not be construed that compliance to ARINC 653 assures robust partitioning.

Purpose

This document specifies the baseline operating environment for application software used within Integrated Modular Avionics (IMA) and traditional ARINC 700-series avionics.

The primary objective of this Specification is to define a general-purpose APEX (APplication/EXecutive) interface between the Operating System (O/S) of an avionics computer resource and the application software. Included within this specification are the interface requirements between the application software and the O/S and the list of services which allow the application software to control the scheduling, communication, and status information of its internal processing elements.

This Specification defines the data exchanged statically (via configuration) or dynamically (via services) as well as the behavior of services provided by the O/S and used by the application. It is not the intent of this specification to dictate implementation requirements on either the hardware or software of the system, nor is it intended to drive certain system-level requirements within the system which follows this standard.

The majority of this document describes the runtime environment for embedded avionics software. This list of services identifies the minimum functionality provided to the application software and is, therefore, the industry standard interface. It is intended for this interface to be as generic as possible, since an interface with too much complexity or too many system-specific features is normally not accepted over a variety of systems. The software specifications of the APEX interface are High-Order Language (HOL) independent, allowing systems using different compilers and languages to follow this interface.

This document is intended to complement ARINC Report 651. It is expected that this document will evolve to contain additional functionality and capability. Supplements to this document will be prepared as needed by the industry.