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114 CHAPTER THREE
Here are a couple of recent web sites with lists of embedded processors that could be
considered. The lists are neither exhaustive nor are they correct, but it’s a place to start:
www.e-insite.net/ednmag/index.asp?layout=article&stt=000&articleid=
CA245647&pubdate=10/3/2002
www.cera2.com/micr/index.htm
We should observe certain rules during the selection process:

Make sure none of the requirements of the design are too restrictive. If the design
requirements are so tight as to eliminate all but one candidate, then change the
design. If the design or components have no wiggle room, the project is much
more likely to run into problems.
Make sure that any processor candidate exceeds most of the requirements by a
good margin.
Don’t spend a massive amount of time on the selection process. Among the final
candidates, more than one perfectly good choice should be available.
Prioritize the requirements. No processor will be a perfect fit for the requirements. If
the most important requirements are identified, it may help to make the choice clear.
Several possible strategies can be used for any search. Here are a few pointers that
can be used during the process:

If the project advisors suggest a specific candidate, consider it for final selection
and require the other candidates to knock it out of the number one spot by exhibit-
ing clearly superior characteristics.
Another alternative is simply to disqualify candidates until few are left. The search
process itself involves solving a number of problems simultaneously. The speci-
fications for the robot and for the control algorithms impose many constraints on
the processor selection process. Each constraint can be used to eliminate many
candidates.
Consider starting with the constraint that is the hardest to overcome. Often, the
most difficult constraint will eliminate most of the processor candidates. The
quicker we can narrow the field down to a very few candidates, the less work the
selection process will take up.

CONSTRAINTS
What are the sorts of constraints commonly considered during the selection of a proces-
sor? The following pages contain a basic checklist of things to look into when select-
ing a computer.