OSEK/VDX [1] is a joint project of the automotive industry that aims to the definition of an industry standard for an open-ended architecture for distributed control units in vehicles.
The objective of the standard is to describe an environment which supports efficient utilization of resources for automotive control unit application software. This standard can be viewed as a set of API for real-time operating system (OSEK) integrated on a network management system (VDX) that together describes the characteristics of a distributed environment that can be used for developing automotive applications.
The typical applications that have to be implemented have tight real-time constraints and an high criticality (for example, a power-train application). Moreover, these applications have to be made in a huge number of unit, therefore there is a need to reduce the memory footprint to a minimum enhancing as possible the OS performance.
Here are some keywords that helps to better characterize the philosophy that drove the main architectural choices of the OSEK Operating System:
The operating system is intended for use on a wide range control units (either system with minimal hardware resources like RAM, ROM, CPU time, i.e. 8 bit microcontrollers). To support a wide range of systems the standard defines four conformance classes that tightly specifies the main features of an OS. Note that memory protection is not supported at all.
The standard specifies an ISO/ANSI-C interface between the application and the operating system that is identical in all the implementations of the OS. The aim of this interface is to give the ability to transfer an application software from one ECU to another ECU without bigger changes inside the application. Due to the wide variety of hardware where the OS has to work in, the standard does not specify any interface for the Input/Output subsystem. Note that this fact reduces (if not prohibits) the portability of the application source code, since the I/O system is one of the main software part that impacts on the architecture of the software. We can say that the prime focus is not to achieve 100% compatibility between the application modules, but to ease their direct portability between compliant operating systems.
Another prerequisite needed to adapt the OS to a wide range of hardware is a high degree of modularity and configurability. This configurability is reflected by the toolchain proposed by the OSEK standard, where some configuration tools help the designer in tuning the system services and the system footprint. Moreover, a language called OIL (OSEK Implementation Language) is proposed to help the definition of a standardized configuration information.
All the OS objects and features are statically allocated. This fact allow to simplify all the OS: the number of application tasks, resources and services requested are defined at compile time. Note that this approach ease the implementation of an OS capable of running on ROM, and moreover it is completely different from a dynamic approach followed in other OS standards like for example POSIX.
The OSEK Standard provides the specification of OSEKTime OS, a time triggered OS that can be fully integrated in the OSEK/VDX framework.
In the following sections the main features of the OSEK/VDX standard will be analyzed in detail.
| [1] | The term OSEK means ``Offene Systeme und deren Schnittstellen für die Elektronik im Kraftfahrzeug'' (Open systems and the corresponding interfaces for automotive electronics); the term VDX means Vehicle Distributed eXecutive. This chapter shortly describe the specification of the Operating System Specification, release 2.2, and recalls some other OSEK documents. |