Using Dual Priority scheduling to improve the resource utilization in the nMPRA microcontrollers

The current practice in most of the safety-critical areas, including automotive, avionics systems and factory automation, encouraging the use of real-time time-trigger schedulers that does not allow interference to take place between safety-critical components and non-critical. Furthermore, in these systems the lack of interference between safety-critical components and non-critical components is achieved by a strict isolation between components with different degrees of severity. This approach can assure, easily, the certification of the safety-critical functionality, but leads to very low resource utilization. For this purpose it will be presented a solution that when the system enters into a state that is different from the normal running state (test service), allowing relaxation and a change in the activation time of tasks (release) violating the fixed priorities scheduling, but avoiding starvation of the system tasks. The proposed solution modifies a static scheduler in a dynamic scheduler depending on the system status using Dual Priority scheduling. The algorithm has been proposed to be implemented on a nMPRA processor, by multiplying hardware resources (PC, pipeline registers and file registers) and other facilities (events, mutexes, interrupts, IPC communication, timer´s, the static scheduler and support for dynamic scheduler) provides a switching and response time for events within 1 to 3 machine cycles.