Arrival Order Processing of Service Requests in Full Hardware Implementation of RTOS-Based Systems

As an approach to drastically enhance the response performance of RTOS-based systems, Oosako proposed a full hardware scheme in which all the tasks/handlers as well as RTOS functions are implemented by hardware. In the architecture proposed so far to realize this hardware scheme, however, service requests from tasks were processed only in the order of tasks' priorities, while some RTOSs stipulate services must be processed in the order of arrival of requests. This paper proposes a hardware mechanism to enable both priority order processing and arrival order processing so that the processing order is selectively defined service by service. This is realized by newly designing an arrival order recording hardware and extending the function of the request arbitration module and flag registers to record the waiting tasks. Based on the proposed method, a management hardware that provides the functions of TOPPERS/ASP3 has been designed in Verilog HDL. The new feature has been successfully implemented, at the cost of 2.6% increase in circuit size.