Time-triggered Architecture

Time-triggered architecture (abbreviated as TTA), also known as a time-triggered system, is a computer system that executes one or more sets of tasks according to a pre-determined and set task schedule.Pont, M.J. (2001) "Patterns for Time-Triggered Embedded Systems", Addison-Wesley / ACM Press. . Implementation of a TT system will typically involve use of a single interrupt that is linked to the periodic overflow of a timer. This interrupt may drive a task scheduler (a restricted form of real-time operating system). The scheduler willin turnrelease the system tasks at predetermined points in time.

History and development

Because they have highly deterministic timing behavior, TT systems have been used for many years to develop safety-critical aerospace and related systems.Ward, N. J. (1991) "The static analysis of a safety-critical avionics control system", in Corbyn, D.E. and Bray, N. P. (Eds.) "Air Transport Safety: Proceedings of the Safety and Reliability Society Spring Conference, 1991" Published by SaRS, Ltd.

An early text that sets forth the principles of time triggered architecture, communications, and sparse time approaches is ''Real-Time Systems: Design Principles for Distributed Embedded Applications'' in 1997.Kopetz, H. (1997) "Real-Time Systems: Design Principles for Distributed Embedded Applications", Springer International Series in Engineering and Computer Science. .

Use of TT systems was popularized by the publication of ''Patterns for Time-Triggered Embedded Systems'' (PTTES) in 2001 and the related introductory book ''Embedded C'' in 2002.Pont, M.J. (2002) "Embedded C", Addison-Wesley. . The PTTES book also introduced the concepts of time-triggered hybrid schedulers (an architecture for time-triggered systems that require task pre-emption) and shared-clock schedulers (an architecture for distributed time-triggered systems involving multiple, synchronized, nodes).

Since publication of PTTES, extensive research work on TT systems has been carried out.Phatrapornnant, T. and Pont, M.J. (2006) "Reducing jitter in embedded systems employing a time-triggered software architecture and dynamic voltage scaling", IEEE Transactions on Computers, 55(2): 113–124.

Current applications

Time-triggered systems are now commonly associated with international safety standards such as IEC 61508 (industrial systems), ISO 26262 (automotive systems), IEC 62304 (medical systems) and IEC 60730 (household goods).

Alternatives

Time-triggered systems can be viewed as a subset of a more general event-triggered (ET) system architecture (see event-driven programming).

Implementation of an ET system will typically involve use of multiple interrupts, each associated with specific periodic events (such as timer overflows) or aperiodic events (such as the arrival of messages over a communication bus at random points in time). ET designs are traditionally associated with the use of what is known as a real-time operating system (or RTOS), though use of such a software platform is not a defining characteristic of an ET architecture.

See also

* Event-driven programming (an alternative architecture for computer systems)
* IEC 61508 (a related safety standard)
* ISO 26262 (a related safety standard)
* DO-178C (a related safety standard)
* Life-critical system (a common application for TT architectures)

References

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Software architecture
Safety
Safety engineering
International standards
Electrical standards
IEC standards
Automotive standards
Automotive safety
Networks