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
A real-time operating system (RTOS) is an operating system (OS) for real-time applications that processes data and events that have critically defined time constraints. An RTOS is distinct from a time-sharing operating system, such as Unix, which m ...
). 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
A safety-critical system (SCS) or life-critical system is a system whose failure or malfunction may result in one (or more) of the following outcomes:
* death or serious injury to people
* loss or severe damage to equipment/property
* environme ...
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
IEC 61508 is an international standard published by the International Electrotechnical Commission consisting of methods on how to apply, design, deploy and maintain automatic protection systems called safety-related systems. It is titled ''Functio ...
(industrial systems),
ISO 26262
ISO 26262, titled "Road vehicles – Functional safety", is an international standard for functional safety of electrical and/or electronic systems that are installed in serial production road vehicles (excluding mopeds), defined by the Interna ...
(automotive systems),
IEC 62304 (medical systems) and
IEC 60730
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(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
In computer programming, event-driven programming is a programming paradigm in which the flow of the program is determined by events such as user actions ( mouse clicks, key presses), sensor outputs, or message passing from other programs or t ...
).
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
A real-time operating system (RTOS) is an operating system (OS) for real-time applications that processes data and events that have critically defined time constraints. An RTOS is distinct from a time-sharing operating system, such as Unix, which m ...
(or RTOS), though use of such a software platform is not a defining characteristic of an ET architecture.
See also
*
Event-driven programming
In computer programming, event-driven programming is a programming paradigm in which the flow of the program is determined by events such as user actions ( mouse clicks, key presses), sensor outputs, or message passing from other programs or t ...
(an alternative architecture for computer systems)
*
IEC 61508
IEC 61508 is an international standard published by the International Electrotechnical Commission consisting of methods on how to apply, design, deploy and maintain automatic protection systems called safety-related systems. It is titled ''Functio ...
(a related safety standard)
*
ISO 26262
ISO 26262, titled "Road vehicles – Functional safety", is an international standard for functional safety of electrical and/or electronic systems that are installed in serial production road vehicles (excluding mopeds), defined by the Interna ...
(a related safety standard)
*
DO-178C
DO-178C, Software Considerations in Airborne Systems and Equipment Certification is the primary document by which the certification authorities such as FAA, EASA and Transport Canada approve all commercial software-based aerospace systems. The do ...
(a related safety standard)
*
Life-critical system
A safety-critical system (SCS) or life-critical system is a system whose failure or malfunction may result in one (or more) of the following outcomes:
* death or serious injury to people
* loss or severe damage to equipment/property
* environme ...
(a common application for TT architectures)
References
{{reflist
Software architecture
Safety
Safety engineering
International standards
Electrical standards
IEC standards
Automotive standards
Automotive safety
Networks