Real-Time Optimization of TTCAN Networks 2008-01-0275
Controller Area Network is widely used as a communications network in automotive applications and operates either by spontaneous or time triggered messaging. Time triggered messaging is the preferred option on modern systems as it allows all messages access to the bus at some defined period in time. Using time triggered messaging alone does not allow real-time access to the network, therefore spontaneous messaging is used in conjunction with the time triggered messaging to ensure a real-time system.
Schedulers are essentially designed to load balance system resources and presently there are two types of schedulers available for the development of TTCAN message sets. They are the Stochastic and Heuristic scheduler, which are both useful, but they do not provide the capability of ensuring real-time messages arrive within their deadline.
Stochastic schedulers generate message sets by a probability distribution and heuristic schedulers develop a message set solution by trial and error. They both define the optimum message set as the one with the least jitter by use of a cost function analysis, but neither scheduler can take into account the effect the schedule may have on spontaneous real-time messaging.
The ideal TTCAN message schedule is one where all messages are separated by the same size arbitration windows. This provides the optimum real-time performance. However with messages of different time periods being broadcast, it should be realized that arbitration windows will nearly always be of different sizes. This paper outlines the development of a new statistical message scheduler. This scheduler has been devised and demonstrated to produced an optimum message set for real-time operation on a TTCAN network and hence improve the results produced by stochastic or heuristic techniques.