# 7.2 Lab  (Page 7/11)

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Does the output match your expectations based on the theory? Does this application illustrate any limitations of the FFT implementation?(Hint: note that most of the values in the FFT input are zero.) The previously-given C implementation uses a similar algorithm as theTI FFT; take a look at the C code for help. What are the limitation(s) of the FFT that show up in this application?

In lab4b.h M sets the number of autocorrelation points that are calculated. What is the maximum valueof M that allows the reference routines to run in real time? In determining this value you may find it useful to connect awave-function generator to the input and copy inputs into display_inputs . You may limit M to powers of 2 minus 1 .

## Quiz information

From your prelab experiments, you should be able to describe the effect of windowing and zero-padding on FFT spectralanalysis. In your DSP system, experiment with different inputs, changing $N$ and the type of window. Can you explain what happens as the input frequency is increased beyond the Nyquist rate? Does the $\left|X(k)\right|^{2}$ coincide with what you expect from Matlab? What is the relationship between the observed spectrum and the DTFT?What would happen if the FFT calculation takes longer than it takes to fill inputs with $N$ samples? How long does it take to compute each FFT? What are the tradeoffs between writing code in C versus assembly?

## Appendix a:

1 /* v:/ece420/54x/dspclib/lab4main.c */ 2 /* dgs - 9/14/2001 */ 3 /* mdk - 2/10/2004 C FFT update */ 4 5 #include "v:/ece420/54x/dspclib/core.h" 6 7 /* comment the next line to use assembly fft */ 8 #define C_FFT 9 10 #ifdef C_FFT /* Use C FFT */ 11 12 #include "window.h" 13 #include "lab4.h" /* Number of C FFT points defined here */ 14 15 /* function defined in lab4fft.c */ 16 void fft(void); 17 18 /* FFT data buffers */ 19 int real[N]; /* Real part of data */ 20 int imag[N]; /* Imaginary part of data */ 21 22 #else /* Use assembly FFT */ 23 24 #define N 1024 /* Number of assembly FFT points */ 25 26 /* Function defined by c_fft_given.asm */ 27 void bit_rev_fft(void); 28 29 /* FFT data buffers (declared in c_fft_given.asm) */ 30 extern int bit_rev_data[N*2]; /* Data input for bit-reverse function */ 31 extern int fft_data[N*2]; /* In-place FFT & Output array */ 32 extern int window[N]; /* The Hamming window */ 33 34 #endif /* C_FFT */ 35 36 37 /* Our input/output buffers */ 38 int inputs[N]; 39 int outputs[N]; 40 41 volatile int input_full = 0; /* volatile means interrupt changes it */ 42 int count = 0; 43 44 45 interrupt void irq(void) 46 { 47 int *Xmitptr,*Rcvptr; /* pointers to Xmit & Rcv Bufs */ 48 int i; 49 50 static int in_irq = 0; /* Flag to prevent reentrance */ 51 52 /* Make sure we're not in the interrupt (should never happen) */ 53 if( in_irq ) 54 return; 55 56 /* Mark we're processing, and enable interrupts */ 57 in_irq = 1; 58 enable_irq(); 59 60 /* The following waitaudio call is guaranteed not to 61 actually wait; it will simply return the pointers. */ 62 WaitAudio(&Rcvptr,&Xmitptr); 63 64 /* input_full should never be true... */ 65 if( !input_full ) 66 { 67 for (i=0; i<BlockLen; i++) 68 { 69 /* Save input, and echo to channel 1 */ 70 inputs[count] = Xmitptr[6*i] = Rcvptr[4*i]; 71 72 /* Send FFT output to channel 2 */ 73 Xmitptr[6*i+1] = outputs[count]; 74 75 count++; 76 } 77 } 78 79 /* Have we collected enough data yet? */ 80 if( count >= N ) 81 input_full = 1; 82 83 /* We're not in the interrupt anymore... */ 84 disable_irq(); 85 in_irq = 0; 86 } 87 88 89 main() 90 { 91 /* Initialize IRQ stuff */ 92 count = 0; 93 input_full = 0; 94 SetAudioInterrupt(irq); /* Set up interrupts */ 95 96 while (1) 97 { 98 while( !input_full ); /* Wait for a data buffer to collect */ 99 100 /* From here until we clear input_full can only take * 101 * BlockLen sample times, so don't do too much here. */ 102 103 /* First, transfer inputs and outputs */ 104 105 #ifdef C_FFT /* Use C FFT */ 106 /* I n s e r t c o d e t o f i l l */ 107 /* C F F T b u f f e r s */ 108 109 #else /* Use assembly FFT */ 110 /* I n s e r t c o d e t o f i l l */ 111 /* a s s e m b l y F F T b u f f e r s */ 112 113 #endif /* C_FFT */ 114 115 /* Done with that... ready for new data collection */ 116 count = 0; /* Need to reset the count */ 117 input_full = 0; /* Mark we're ready to collect more data */ 118 119 /**********************************************************/ 120 /* Now that we've gotten the data moved, we can do the */ 121 /* more lengthy processing. */ 122 123 #ifdef C_FFT /* Use C FFT */ 124 125 /* Multiply the input signal by the Hamming window. */ 126 /* . . . i n s e r t C / a s m code . . . */ 127 128 /* Bit-reverse and compute FFT in C */ 129 fft(); 130 131 /* Now, take absolute value squared of FFT */ 132 /* . . . i n s e r t C / a s m code . . . */ 133 134 /* Last, set the DC coefficient to -1 for a trigger pulse */ 135 /* . . . i n s e r t C / a s m code . . . */ 136 137 /* done, wait for next time around! */ 138 139 140 #else /* Use assembly FFT */ 141 142 /* Multiply the input signal by the Hamming window. */ 143 /* . . . i n s e r t C / a s m code . . . */ 144 145 /* Bit-reverse and compute FFT in assembly */ 146 bit_rev_fft(); 147 148 /* Now, take absolute value squared of FFT */ 149 /* . . . i n s e r t C / a s m code . . . */ 150 151 /* Last, set the DC coefficient to -1 for a trigger pulse */ 152 /* . . . i n s e r t C / a s m code . . . */ 153 154 /* done, wait for next time around! */ 155 156 157 #endif /* C_FFT */ 158 159 } 160 }

#### Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
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?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
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
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
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
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
how did you get the value of 2000N.What calculations are needed to arrive at it
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