Input and Output with the DSK - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 63

product of the carrier and baseband signals (within the output equation) is scaled
by 2 12 (shifted right by 12). Projects on modulation are included in Chapter 10.

Example 2.15: Sweep Sinusoid Using a Table with
8000 Points ( sweep8000 )

Figure 2.24 shows a listing of the program sweep8000.c , which generates a sweep-
ing sinusoidal signal using a table lookup with 8000 points. The header file
sine8000_table.h contains the 8000 data points that represent a one-cycle sine
wave. Since the output rate is F s

8 kHz, 8000 points are chosen to represent a
1-second interval. The file sine8000_table.h (in the folder sweep8000 ) is gen-
erated with MATLAB using

=

1000*sin(2*pi*i*start_freq/8000)

// Sweep8000.c Sweep sinusoid using table with 8000 points

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
#include "sine8000_table.h" //one cycle with 8000 points
short start_freq = 100; //initial frequency
short stop_freq = 3500; //maximum frequency
short step_freq = 200; //increment/step frequency
short amp = 30; //amplitude
short delay_msecs = 1000; //# of msec at each frequency
short freq; //variable frequency

short t;
short i = 0;

void main()
{
comm_poll(); //init DSK, codec, McBSP
while(1) //infinite loop

{
for(freq=start_freq;freq<=stop_freq;freq+=step_freq)
{ //step thru freqs
for(t=0; t<8*delay_msecs; t++) //output 8*delay_msecs samples
{ // at each freq
output_sample(amp*sine8000[i]);//output
i = (i + freq) % 8000; //next freq sample
}
}
}
}

FIGURE 2.24. Program to generate a sweeping sinusoid using a lookup table with 8000
points ( sweep8000.c ).