VAXELN Experimentation: Programming a Real-Time Periodic Task Dispatcher Using VAXELN Ada 1.1

Abstract

The ideas and findings in this report should not be construed as an official DoD position. It is published in the interest of scientific and technical information exchange. Review and Approval This report has been reviewed and is approved for publication. FOR THE COMMANDER

Aperiodic task scheduling for Hard-Real-Time systems

“…In fact, with the period transformation method, the utilization threshold can, in principle, be arbitrarily close to 100 % (Sha and Goodenough 1988). As an example of the high degree of schedulable utilization attainable with the rate monotonic algorithm, a schedulable utilization level of 99 % was achieved for the Navy's Inertial Navigation System (Borger 1987).…”

Scheduling Sporadic and Aperiodic Events in a Hard Real-Time System

“…For simplicity, we assume that periodic tasks have hard deadlines and constant execution times. 1 In Chapter 2 we will review related work on scheduling periodic and aperiodic tasks. Chapter 3 introduces the Sporadic Server (SS) algorithm for scheduling aperiodic tasks and illustrates its operation with several examples.…”

“…In fact, with the period transformation method, the utilization threshold can, in principle, be arbitrarily close to 100% [9]. As an example of the high degree of schedulable utilization attainable with the rate monotonic algorithm, a schedulable utilization level of 99% was achieved for the Navy's Inertial Navigation System [1].…”

“…Task x 1 has the shorter period and thus is assigned a higher priority than task x 2 by the rate monotonic algorithm. For these examples both t 1 For this periodic task set, the maximum server sizes were determined for the DS, PE, and SS algorithms. For each algorithm the server's period was chosen to be 5 units of time.…”

Real-time software engineering in Ada: observations and recommendations

“…If this conditional entry call fails, the periodic task has missed a deadline and appropriate action can be taken. Details on how to implement this periodic tasking scheme in Ada are explained by Borger [2].…”