As mentioned above rectangle.c will also toggle the parallel port, but it will do it load independent, so if rectangle.o is running on the second PC then you will not be able to timeout rt_irq_gen.o on the MiniRTL system. At the same time rectangle.c is an example of simple real time multitasking. Two threads are running, one that sets the pins D0-D7 ''Hi'' and one that set them ''Lo''.