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In this lab we will focus on improving the performance of the MSP and attempt to optimize your code.

So far in this course, programming assignments have focused on functionality. In most applications of embedded programming, speed and power performance are equally important. Long battery life is won through judicious hardware and software design. Skillful programming will allow the same job to be done with cheaper parts to improve the bottom line. This lab will introduce the basic concepts behind power and speed performance improvement.

Speed performance

It is well known from the consumer PC market that the speed of computers can be measured in hertz. It is less well known that the frequency of the computer's processor does not adequately indicate a computer's performance or even the performance of the processor itself. By using the ELEC226 board, the choice of processor and speed has been made, but the question of speed is a different one in embedded programming. While the dominant paradigm in consumer personal computing is to increase the performance of the computer to allow the system to do more with each generation, embedded processors are chosen to be able to perform specific tasks. The cheapest processor that can meet the specifications for the design will be chosen. While the issue and business conditions make the situation much more complicated than just price, the pressure is still toward choosing a part with less performance, not more.

In order to improve the performance of a software application, it is necessary to understand the way performance is measured. Measuring performance between platforms and software packages is a problematic endeavor, improving the performance of a single program on a single platform is much simpler. a detailed explanation of the nuances of performance measurement in computing is beyond the scope of this lab, simple way to gauge the amount of time a program will take to perform a task is to count the number of processor cycles that the code will take. On the MSP430, each CPU instruction, jump, and interrupt takes a fixed number of cycles as explained in the MSP430 User’s Guide. Taking into account branching, function calls, and interrupts the assembly code of a program can be used to calculate the time needed for a section of code.

Performance tips

As mentioned above, embedded programming has different priorities from personal computing. Because the embedded programmer is usually trying to accomplish a specific task within a certain amount of time, the most important test of performance is whether the program is performing calculations on the inputs as fast as the inputs can enter the system. The goal is to make applications " real time ."

When the first draft of a program is unable to keep up with the required sampling, it is necessary to reduce execution time. Often, changing the hardware configuration is not possible; and software speed gains are almost always more cost effective.

There are many approaches to improving speed performance. Incredible amounts of research go into new algorithms for common problems to improve the way that problem is solved. However, simply eliminating unnecessary instructions is a good start to improving performance. Test code left in a final version, any unnecessary instructions in a loop, and can all significantly increase the time in a section of code.

In C, unnecessary code takes the form of too many method calls inside of a loop because each function call costs additional instructions. While this is not an important loss for code that is only executed once per sample, in loops that run often, every little gain counts much more. When trying to reduce execution time, it is best to start with the regions of the code where the processor spends the most time. Parts of the program that are only executed rarely have only a small effect on the speed compared to a loop that might run 100 times per sample. If something can be done once, outside of the loop, do not do it many times inside the loop.

Another straightforward way to maximize performance on the hardware provided is to make judicious use of timers and other instruction saving interrupts. The timer interrupts allow the processor to periodically check on the status of the program without the use of slow while () loops. However, for correct program behavior, it is important to do the minimum possible in the interrupt. This is most important with interrupts that happen frequently because the control flow of the program can be thrown off when interrupts happen faster than the system can handle them. If the same interrupt occurs a second time before the first occurrence of the interrupt has exited there, program behavior is much more difficult to control. It is much easier to simply ensure that the interrupt is short enough to avoid the danger all together.

Avoid recalculating values. If a piece of information is reusable, save it rather than recalculating it to save time. Sometimes memory is so scarce that this may not be possible.

Don’t use the printf function unless you absolutely must. It can be quite slow if used repeatedly. Use breakpoints instead.

Don’t leave legacy code from previous revisions running. If you believe you may no longer need a part of the program, comment it out and note what you did in the comments.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Microcontroller and embedded systems laboratory. OpenStax CNX. Feb 11, 2006 Download for free at http://cnx.org/content/col10215/1.29
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