SOFTWARE OPTIMIZATION TECHNIQUES - Software Design for Six-Sigma: A Roadmap for Excellence - page 447

Utilization % Zone Type Type of Application

0-25 CPU under utilized General purpose

25-50 Very safe ,,

51-68 Safe ,,

69 Theoretical limit Embedded system

700-82 Questionable Embedded system

83-99 Dangerous Embedded system

FIGURE 17.3 Typical CPU utilization zones and typical applications
and recommendations.

The following is a simple example of a background loop:

int main( void )
{

SetupInterrupts();
InitializeModules();
EnableInterrupts();
while(1) /* endless loop - spin in the background */
{
CheckCRC();
MonitorStack();
... do other non time critical logic here.
}

}

This depiction is an oversimplification, as some kind of work often is done in the
background task. However, the logic coded for execution during the idle task must
have no hard real-time requirements. In fact, one technique that may be used in an
overloaded system is to move some of the logic with less strict timing requirements
out of the hard real-time tasks and into the idle task.

17.3.4 Memory Requirements

A system's memory can be important for a real-time system, as a computer's memory
directly can influence the performance of a real-time system. In particular, a system's
memory can affect access time. Access time is defined as the interval between when a
datum is requested and when it is available to the CPU. The effective access time may
depend on the memory type as well as the memory technology, the memory layout,
and other various factors. In the last few years, memory has become cheaper and more
plentiful. Thus, memory has become less of an issue than it was a decade or two ago.
However, embedded real-time systems must be small, inexpensive, and efficient.