# 9.3 Lab 9: optimization and low power modes

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In this lab, we will learn the basics of optimizing code intended for embedded systems.

## Fibonacci optimization

The " Reducing Power Consumption " module discusses why it is important to keep power in mind when programming embedded devices. We have yet to consider this while programming the previous labs. Writing efficient code is the first step in improving power consumption, next we can disable all parts of the board that aren't currently being used.

Take the following piece of code: ```long fibo(int n) { if (n < 2) return n; else return fibo(n-1) + fibo(n-2); }``` It recursively calculate the nth number in a Fibonacci sequence recursively. Recursion makes this piece of code easier to read, however, it is very inefficient and consumes far more memory than it has to. If you try to compute a large number, say `fibo(50)` , then it will take much longer and will consume more power than it should.

The original program is very inefficient and wastes memory in several of the ways described in the inefficient Memory Conservation module. Modify the code to eliminate the memory waste and improve the speed of the program. Note that there is a tradeoff between speed and memory (though at first the program is simply gratuitously wasteful). What is the nature of the tradeoff? Assuming the one addition takes one cycle to complete, how long would it take the original code to complete `fibo(50)` ? How long would it take your new, improved version? Assume that you are only considering the addition operations.

## Low power modes

Modify your project so that the processor remains in one of the low power modes whenever it is not doing any calculations. Wake up from low power mode when a pushbutton interrupt fires, and have your program compute `fibo(50)` . Output the result to the standard out display. What is the result? (Hint: 12,586,269,025) Make the result is correct number. As soon as the calculation is done, return to low power mode. Make sure to turn on the Red LED while in an idle state.

A number must be small enough to fit in its given type. If it is too large, you may get unpredictable results. Try using a `long long` for extra huge numbers. If your standard out does not support such large data types then you may have to use bit-wise operations to separate the number into smaller chunks suitable for printing.

Measure the power consumed by the entire device when you are in low power mode and when it is computing something. You may want to have the processor compute something indefinitely, in order to get a more accurate result.

what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
how did you get the value of 2000N.What calculations are needed to arrive at it
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