Domain Function and Scheduling Method to Achieve Safety in Embedded Systems

This paper proposes a scheduling method with a domain system for safety related tasks in order to prevent interference from non-safety-related interrupt handlers. There is a growing demand for safety on embedded real-time systems. Safety-related tasks must run with specific deadlines since their processes, such as a process handling system failure, prevent catastrophic damages to life, the environment and property. On the other hand, many real-time operating systems have a function to manage interrupt handlers which are triggered by hardware interrupts. The problem of the interrupt handler is that the non-safety-related interrupt handler interferes with the safety-related tasks because the interrupt processing is immediately executed. This paper proposes a domain system and a scheduling method based on the preemptive and priority-based scheduling considering a degree of safety. Domains are categorized into safety domains and normal domains. Every task and every interrupt handler belongs to one domain. The interrupt handlers and tasks are scheduled considering priority, the safety type of the domain and the object type. With this scheduling, a task in a safety domain is executed before an interrupt handler in a normal domain. By measuring the execution time of tasks in the safety domain, we show that our scheduling method prevents the interrupt handlers in normal domains from interfering with safety domain task execution.