ABSTRACT
Using the standard programming approach the modules shown in Figure 2 are treated as procedures or subroutines o f a single main program. The flow o f such a program is illustrated in Figure 3. This structure is easy to program. However, i t imposes the most severe o f the real-time constraints, that is, the requirement that the clock module must run every 20 ms on all o f the modules. For the system to work the clock module and any one o f the other modules must complete their op erations wi thin 20 ms. I f th t2 t4, t5 and t6 are the maximum execution times for the modules clock, speed control, logic control, operator display, operator input and message communication respectively then a requirement for the system to work can be expressed as:
ti + M A X (t2, t3, U, t5, t6) < 20 ms
