Page 40 - Embedded Microprocessor Systems Real World Design

Since there are fewer oscillators, there usually will be less EMI. On the other
hand, a faster processor may be required, operating at a higher frequency and
generating a lot of EMI.
If the design changes so that intertask communication must be added, such as
for motor synchronization, a distributed design may require that interfaces be
added to each distributed CPU. In a single-CPU design, such a change is likely
to be only to the software.
It is easier to download or update code in a single-CPU system.
Debug of a single-CPU system may be easier since all the functions are in a single
place and all the interactions can be examined. Of course, these interactions as
well as the task switching and general complexity of the code can complicate
debug as well.
Fewer development tools are needed since there is only one processor. In a dis-
tributed system, the same thing can be achieved by using only one type of CPU;
however, this defeats the ability to match the CPU to the task.
If an RTOS is used, there will be fewer license fees in a single-CPU system.
However, a more complex, more expensive RTOS may be required.
With increasing processor power at decreasing cost, I think more single-CPU
designs are to be expected. Some designs will take advantage of increased CPU
horsepower to add new functions, such as real-time signal processing. But motors
and other electromechanical devices are getting no faster, so systems that interact
with these devices probably will use fewer, more powerful processors. Complex
systems that use a single Pentiumclass CPU and a few 8-bit microcontrollers as
smart sensors would not be surprising.

Specifications Summary

Let’s summarize the contents of the design documents described in this chapter
before we look at the actual design in the rest of the book.
The requirements document describes:
What the design or system is to do
The user interface, if any
Any external interfaces to other systems
What the real world I/O consists of

Hardware specifications (one per board or subsystem) describe:
The requirements, restated from engineering or requirements documents
How the hardware implements the functionality
The software interfaces to the hardware

System Design 25