<< Chapter < Page Chapter >> Page >

Parameter passing

The parameter passing convention between assembly and C is simple for single input, single output assembly functions.From a C program, the input to an assembly program is in the low part of accumulator A with the output returned in the same place. In this example, the function filter takes the right input sample from A and returns a single output in A (note the left shift by 16 to put the result in the low part of A ). When more than one parameter is passed to an assembly function, the parameters are passed on thestack (see the core file description for more information). We suggest that you avoid passing or returning more than oneparameter. Instead, use global memory addresses to pass in or return more than one parameter. Another alternative isto pass a pointer to the start of a buffer intended for passing and returning parameters.

Registers modified

When entering and leaving an assembly function, the ENTER_ASM and LEAVE_ASM macros ensure that certain registers are saved and restored. Sincethe C program may use any and all registers, the state of a register cannot be expected to remain the same between callsto assembly function(s). Therefore, any information that needs to be preserved across calls to anassembly function must be saved to memory! In this example, stateptr keeps track of the location of the current sample in the circular buffer firstate . Why don't we need to keep track of the location of the coefficient pointer ( AR2 in this example) after every sample?

Compiling and linking

A working program can be produced by compiling the C code and linking assembly modules and the core module. Thecompiler translates C code to a relocatable assembly form. The linker assigns physical addresses on the DSP to therelocatable data and code segments, resolves .global references and links runtime libraries.

The procedure for compiling C code and linking assembly modules has been automated for you in the batch file v:\ece320\54x\dsptools\C_ASM.bat . Copy the files lab3main.c , and lab3filt.asm from the v:\ece320\54x\dspclib\ directory into your own directory on the W: drive. Using Matlab, write the coefficients you created in the prelabinto a coef1.asm file. Then, type c_asm lab3main lab3filt to produce a lab3main.out file to be loaded onto the DSP. Load the output file onto the DSP as usual and check that isthe FIR filter you designed.

Cascade of fir1 and fir2

Modify the lab3filt.asm assembly module to implement a cascade of filters FIR1 and FIR2. Note thatboth _filter and _init_filter will need to be modified. Compile and link the new assemblymodule and confirm it has the frequency response which you expect from cascading FIR1 and FIR2.

Complete multirate system

Once you have the cascaded system working, implement the multirate system composed of the three FIR filters bymodifying the assembly modules in lab3filt.asm . In order to implement the sample rate converters, you willneed to use a counter or a loop. The upsampling block and downsampling block are not implemented as seperatesections of code. Your counter or loop will determine when the decimated rate processing is to occur aswell as when to insert zeros into FIR3 to implement the zero-filling up-sampler.

Some instructions that may be useful for implementing your multirate structure are the addm (add to memory) and bc (branch conditional) instructions. You may also find the banz (branch on auxiliary register not zero) instruction useful, depending on how you implement your code. As the counter is state information that needs to be preservedbetween calls to filter , the counter must be saved in memory.

In order to experiment with multirate effects in yoursystem, make the downsampling factor ( D U ) a constant which can be changed easily in your code. Is there a critical( D U ) associated with this system above which aliasing occurs?

It will be useful both for debugging and for experimentation to show the output of your system at various points in theblock diagram. By modifying the C code in lab3main.c and the assembly modules in lab3filt.asm , send the following sequences to the DSP output

  • output of FIR1
  • input to FIR2 (after downsampling)
  • input to FIR3 (after upsampling)
You will have to pass these samples to the main C program by storing them in memory locations as described in . Note that the input to FIR2 is at the downsampled rate.

Grading and oral quiz

For the quiz, you should be prepared to change the decimation rate upon request, and explain the effects ofchanging the decimation rate on the system's output.

As usual, your grade will be split up into three sections:

  • 1 point: Prelab
  • 4 points: Code (Code which is complete and working at the beginning of the lab period gets fullcredit.)
  • 5 points: Oral Quiz
The oral quiz may cover various problems in multirate sampling theory, as well as the operation of your codeitself and details about the instructions you've used in your code. Be prepared to explain, in detail, the operationof all of your code, even if your lab partner wrote it! You may also be asked to make changes to your code and topredict, and explain, the effects of these changes.

Extra credit: 1 point

One of the main benefits of multirate systems is efficiency. Because of downsampling, the output of FIR1 is used only oneof D times. Make your assembly module more efficient by using this fact.

Similarly, at the input of FIR3, D 1 of every D samples is zero. So, for a fixed downsampling factor D , it is possible to make use of this fact to create D different filters (each a subset of the coefficients of FIR3) to be used at the D time instances. This technique is referred to as polyphase filtering and can be found in most modern DSPtextbooks. These filters are more efficient as the sum of the lengths of the filters is equal to the length of FIR3.Apply this fact for D 4 .

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
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
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
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
Sanket Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Ece 320 - spring 2003. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10096/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ece 320 - spring 2003' conversation and receive update notifications?

Ask