救助 急急急。DSP C5515 怎么调用dsplib 里 rifft（）和cbrev（）转回时域。

Question

代码里已经给出来 fft后，在c5515的显示屏上出现了bargraph的图案，转到了频域。如何再调用dsplib里的rifft（）和cbrev（）转回时域，并且在显示屏上出来正弦波？``代码如下，如果我再写一个ifft的子函数，我是不是要新定义一个buffer 然后input是calculate_power 的buffer？

#include "stdio.h"
#include "usbstk5515.h"
#include "usbstk5515_led.h"
#include "aic3204.h"
#include "PLL.h"
#include "bargraph.h"
#include "oled.h"
#include "pushbuttons.h"
#include "stereo.h"
#include "dsplib.h"

Int16 left_input;
Int16 right_input;
Int16 left_output;
Int16 right_output;
Int16 mono_input;

#define SAMPLES_PER_SECOND 8000

/* Use 20 for guitar */
#define GAIN_IN_dB 0

unsigned long int i = 0;

unsigned int Step = 0;
unsigned int LastStep = 99;

int j = 0;
int k = 0;
int m = 0;
int display_counter = 0;
int waveform_counter;
long delay;

DATA input_buffer[1024]; /* Must be declared as DATA for dsplib compatibility */

DATA buffer2[1024];
int display_buffer[96];
int buffer1[96];

/*****************************************************************************/
/* calculate_power() /
/---------------------------------------------------------------------------*/
/* /
/ Parameter 1: Real term a. /
/ Parameter 2: Immaginary term jb. /
/ /
/ RETURNS: a*a + b*b. Result will always be positive. /
/ /
/****************************************************************************/

int calculate_power (int a, int b)
{

return ( (int) ( ( (long)a * a + (long) b * b) >> 14) );
}

/*****************************************************************************/
/* calculate_FFT() /
/---------------------------------------------------------------------------*/
/* /
/ Parameter 1: Latest audio input (real value). /
/ Parameter 2: size of FFT e.g. 128, 512 and 1024 elements. /
/ /
/ RETURNS: None. /
/ /
/****************************************************************************/

void calculate_FFT(int input, int size)
{
static int i = 0;
static int counter = 0;

buffer2[i] = input; /* Store as a real value /
i++;
buffer2[i] = 0; / Store with an imaginary value of 0 */
i++;

if ( i >= size-1)
{
i = 0;

/* Perform complex FFT using N real and N imaginary values */

cfft (&buffer2[0], size/2, SCALE);

cbrev(&buffer2[0], &buffer2[0], size/2);

for ( j = 0 ; j < 96 ; j ++)
 {
  display_buffer[j] = calculate_power((int) buffer2[2*j], (int)buffer2[2*j+1]); 
 }

counter++;
if ( counter >= 1)
{
  /* Slow down the number of updates to make display easier to see */   
  counter = 0;  
  oled_display_bargraph( &display_buffer[0]);
}     

}
}

/* ------------------------------------------------------------------------ *

• *
• main( ) *
• *

• ------------------------------------------------------------------------ /
  void main( void )
  {
  / Initialize BSL */
  USBSTK5515_init( );

  /* Initialize PLL */
  pll_frequency_setup(120);

  /* Initialise hardware interface and I2C for code */
  aic3204_hardware_init();

  /* Initialise the AIC3204 codec */
  aic3204_init();

  /* Turn off the 4 coloured LEDs */
  USBSTK5515_ULED_init();

  /* Initialise the OLED LCD display /
  oled_init();
  SAR_init();
  / Flush display buffer */
  oled_display_message(" ", " ");

  printf("\n\nRunning Project Spectrum Analyser\n");
  printf( "<-> Audio Loopback from Microphone In --> to Headphones/Lineout\n\n" );

  /* Setup sampling frequency and 30dB gain for microphone */
  set_sampling_frequency_and_gain(SAMPLES_PER_SECOND, GAIN_IN_dB);

  oled_display_message("Application 20 ", "Spectrum Analyser ");

  /* New. Add descriptive text */
  puts("\n Bargraph at 6dB intervals");
  puts("\n Press SW1 for DOWN, SW2 for UP, SW1 + SW2 for reset\n");
  puts(" Step 1 = Straight through, no signal processing. Set levels");
  puts(" Step 2 = Waveform view");
  puts(" Step 3 = FFT 1024 Display. Calculate power and display as bargraph");
  puts(" Step 4 = FFT 512 Display. Calculate power and display as bargraph");

  /* Default to XF LED off */
  asm(" bclr XF");

  for ( i = 0 ; i < SAMPLES_PER_SECOND * 600L ;i++ )
  {

  aic3204_codec_read(&left_input, &right_input); // Configured for one interrupt per two channels.

  mono_input = stereo_to_mono(left_input, right_input);

  Step = pushbuttons_read(4);

  if ( Step == 1 )
  {
  if ( Step != LastStep )
  {
  oled_display_message("STEP1 No Processing", "Set Levels ");
  LastStep = Step;

    } 
   left_output = left_input;      // Straight trough. No processing.
   right_output = right_input;
  
  } 
  

  else if ( Step == 2)
  {
  if ( Step != LastStep)
  {
  oled_display_message("STEP2 ", " Waveform View");
  LastStep = Step;
  display_counter = 0;
  waveform_counter = 0;
  }

   if ( display_counter < 8000)
     {
      display_counter++;
     } 
  
   if (display_counter >= 8000)
     {
      buffer1[k] = mono_input;
      k++;
  
      if ( k >= 96)
       {
         k = 0;   
         waveform_counter++;
         if ( waveform_counter >= 6)
           {
             waveform_counter = 0;    
             oled_display_waveform(&buffer1[0]);
             delay = 0xFFFFFF;
             while ( delay--)
              {
               /* Wait */ 
              }   
           }  
       }
  
     }
  
  } 
  

  else if ( Step == 3)
  {
  if ( Step != LastStep)
  {
  oled_display_message("STEP3 ", " FFT 1024 Display");
  LastStep = Step;
  display_counter = 0;
  }

   if ( display_counter < 8000)
     {
      display_counter++;
     } 
  
   if (display_counter >= 8000)
     {  
      calculate_FFT(mono_input, 1024);
     }
  }  
  

  else if ( Step == 4)
  {
  if ( Step != LastStep)
  {
  oled_display_message("STEP4 ", " FFT 512 Display");
  LastStep = Step;
  display_counter = 0;
  }

   if ( display_counter < 8000)
     {
      display_counter++;
     } 
  
   if (display_counter >= 8000)
     {  
      calculate_FFT(mono_input, 512);
     }                
  
  }   
  

  aic3204_codec_write(left_output, right_output);

  if ( Step == 1)
  {
  /* Only display bargraph when setting up. Distracting otherwise */
  
  bargraph_6dB(left_output, right_output);
  }
  }

  /* Disable I2S and put codec into reset */
  aic3204_disable();

  printf( "\n***Program has Terminated***\n" );

  oled_display_message("PROGRAM HAS ", "TERMINATED ");

  SW_BREAKPOINT;
  }

/* ------------------------------------------------------------------------ *

• *
• End of main.c *
• *
• ------------------------------------------------------------------------ */