Reliability Improvement of the Dual-Priority Protocol under Unreliable Transmission
Résumé
The dual-priority is a scheduling policy providing the guarantees needed by periodic or sporadic hard real-time tasks while decreasing the response time for aperiodic soft real-time tasks. This scheduling policy can be applied to message scheduling and its performance on CAN (Controller Area Network) will be assessed. Nevertheless, when used in an electromagnetic stressed environment (e.g. automotive communication) leading to transmission errors, this scheduling strategy could lead to serious disappointments. It will be explained why the hard real-time traffic is highly sensitive to transmission errors. The risks of deadline failure will be quantified and a simple mechanism that provides probabilistic guarantees to prevent hard real-time frames from missing their deadlines, will be proposed. This mechanism is compared in terms of performance to the original dual-priority strategy. The chosen performance metrics are the deadline failure probability for hard real-time traffic, the average response time and the variance in response time for soft real-time traffic.