Performance evaluation of STRON: A hardware implementation of a real-time OS

In a real-time system, it is required to reduce the response time to an int errupt signal, as well as the execution time of a Real-Time Operating Syste m (RTOS). In order to satisfy this requirement, we have proposed a method o f implementing some of the functionalities of an RTOS using hardware. Based on this idea, we have implemented a VLSI chip, called STRON (silicon TRON: The Realtime Operating system Nucleus), to enhance the performance of an R TOS, where the STRON chip works as a peripheral unit of any MPU. In this pa per we describe the hardware architecture of the STRON chip and the perfor mance evaluation results of the RTOS using the STRON chip. The following re sults were obtained. (1) The STRON chip is implemented in only about 10,000 gates when the number of each object (task, event flag, semaphore, and int errupt) is 7. (2) The task scheduler can execute within 8 clocks in a fixed period using the hardware algorithm when the number of tasks is 7. (3) Mos t of the basic mu ITRON system calls using the STRON chip can be executed i n a fixed period of a few microseconds. (4) The execution time of a system call, measured by a multitask application program model, can be reduced to about one-fifth that in the case of the conventional software RTOS. (5) The total performance, including context switching, is about 2.2 times faster than that of the software RTOS. We conclude that the execution time of the part of the system call implemented by the STRON chip can almost be ignored , but the part of the interface software and context switching related to t he architecture of a MPU strongly influence the total performance of an RTO S.