Computers as Components, 2nd Edition

6.2 Preemptive Real-Time Operating Systems 309

iteration including the execution of several complete processes. Here, the time

quantum is in general smaller than the execution time of any of the processes.

How do we switch between processes before the process is done? We cannot

rely on C-level mechanisms to do so. We can, however, use assembly language to

switch between processes. The timer interrupt causes control to change from the

currently executing process to the kernel; assembly language can be used to save

and restore registers.We can similarly use assembly language to restore registers not

from the process that was interrupted by the timer