From: lex@cc.gatech.edu
Jonathan Griffitts writes:
> I don't think you have grasped the whole "embedded computer" mindset.
[...]
> Your typical design requirement spec for the processor subsystem would
> include something like:
> - 100 square cm of board space is available.
> - You may use a maximum of X Watts, but never for more than XX seconds
[etc]
Right, but so long as the requirements are moderate, then increasing
these specs should simply require more of some components without
changing the overall design. It takes little design effort and only
moderate $$'s to simple have *more* board space, or *more* shielding,
or *more* overall mass. It only becomes a problem if you increase the
requirements by so much that you need a totally new design approach to
power generation or shielding or whatever.
So long as the requirements stay modest -- and I know of know reasons
why they would not be -- then secondary effects just increase the cost
of components without increasing risk or affecting design time. But
I'd love to know more.
> The situation I'm talking about is not limited to space probes, by the
> way. Think about the constraints on the processors in disk drives, or
> inkjet printers, or automobile engine controllers, or cell phones, or
> digital hearing aids, pacemakers, . . . the list is endless.
Mass produced items are different. For mass produced items, the cost
of the components can make a big difference on profits. 10 cents per
wristwatch is a lot, while $10,000 per Mars rover is peanuts. Thus,
for a Mars rover, it is more important to decrease risk and to save
design time, than it is to decrease the cost of components.
Imagine walking into a design meeting and saying you have a way to
save $10,000 in hardware cost, while costing only $10,000 in
development time and increasing the risk of failure by 1%. That would
be persuasive for hearing aids, but not for Mars rovers.
-Lex
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