Input and Output with the DSK - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 55

// Ramptable.c Generates a ramp using a look-up table

#include "dsk6713_aic23.h" //codec-dsk support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
#define table_size (int)0x400 //size of table=1024
short data_table[table_size]; //data table array
int i;

interrupt void c_int11() //interrupt service routine

{
output_sample(data_table[i]);

//ramp value for each Ts

if (i < table_size-1) i++; //if table size is reached

else i = 0; //reinitialize counter

return; //return from interrupt

}

main()
{
for(i=0; i < table_size; i++)
{
data_table[i] = 0x0;

//clear each buffer location

data_table[i] = i * 0x20; //set to 0,32,64,96,..,32736

}
i = 0; //reinit counter

comm_intr(); //init DSK, codec, McBSP

while (1); //infinite loop

}

FIGURE 2.14. Ramp generation program using a lookup table ( ramptable.c ).

Example 2.9: Ramp Generation without a Lookup Table ( ramp )

Example 2.8 is based on loading a table with a set of values, then outputting each
value in the table every sample period, wrapping around when the end of the table
is reached. Figure 2.15 shows a listing of the program ramp.c , which generates a
ramp using an alternative approach to Example 2.8. Starting with an initial output
value of 0, the output value is incremented by 0x20 every sample period T s .The
values sent for output are then 0, 32, 64, 96,...,32,736.
Build and run this project as ramp . Verify that a ramp with a negative slope and
an approximate peak value of 3 V is generated. To obtain a ramp with a positive
slope, change output to

output -= 0x20;

so that the output becomes 0, - 32, - 64,..., - 32,736. Also change the if statement

to reinitialize output ,or

if (output == -0x7FFF)