A timing constraints control technique for embedded real time systems

The real-time applications have a growing complexity and size which have to be well controlled. They can be viewed as a set of synchronized tasks, communicating and sharing critical resources. One of the main difficulties in the real-time application design is time constraints meeting. All tasks have to be running before their predefined deadlines. At this level, the integration of real time operating systems (RTOS) in the real-time systems design flow is necessary to enable scheduling tasks and managing the competition between them with respect of timing constraints. One of the problems encountered here is that one task may have different execution times. It may exceed its predefined WCET and then its deadline for many reasons. The problem is that one deadline exceeding may cause subsequent constraints violations which may disrupt the functioning of the system. This paper deals with this particular issue. It presents a new technique that permits the monitoring of tasks under execution. It controls their timing constraints by means of watchdog concept and detects deadline missing. That information is used to tune the target application parameters in order to satisfy timing constraints for the further computation iterations. We have implemented this technique in the RTOS MicroC/OS-II using the EDF scheduling policy. This technique has been validated using an Altera FPGA prototyping platform and the 3D rendering application.