CCS/TMS320C6713B: Problems using fft function from DSPLIB

Tool/software: Code Composer Studio

Hi,
I have some problems using DSPF_sp_cfftr2_dit function from DSPLIB (dsp67x.lib) in CCS v5.3 (DSK6713). If the following line is included in the code:

DSPF_sp_cfftr2_dit(fft_in, coeffs, wlen);

I am always getting the noise signal from the codec output (even if the fft result is not directed at the headphone output - please see the code below).

I am getting no errors or warnings while building my project. My configuration is:

linker search paths:
- path to dsplib/lib/dsp67x.lib
- path to rts6700.lib

include options:
- path to dsplib/include

#define CHIP_6713 1

#include <stdio.h>
#include <c6x.h>
#include <csl.h>
#include <csl_mcbsp.h>
#include <csl_irq.h>
#include <math.h>

#include "dsk6713.h"
#include "dsk6713_aic23.h"

#include "DSPF_sp_cfftr2_dit.h"
#include "utility.h"


DSK6713_AIC23_CodecHandle hCodec;			    // Codec handle
DSK6713_AIC23_Config config = DSK6713_AIC23_DEFAULTCONFIG;  // Codec configuration with default settings

#define M_PI 3.14159265358979323846
#define wlen 1024
#define hop2 256
#define hop1 203

#pragma DATA_ALIGN(fft_in, 8)
#pragma DATA_ALIGN(coeffs, 8)

volatile float buffer_in[1280];
volatile Uint16 j=0;
volatile Uint8 frame_ready_flag=0;

float fft_in[2*wlen];	// Processing frame
float coeffs[wlen]={0};

interrupt void serialPortRcvISR(void);

void main()
{

	DSK6713_init();		// Initialize the board support library, must be called first
    hCodec = DSK6713_AIC23_openCodec(0, &config);	// open codec and get handle

	// Configure buffered serial ports for 32 bit operation
	// This allows transfer of both right and left channels in one read/write
	MCBSP_FSETS(SPCR1, RINTM, FRM);
	MCBSP_FSETS(SPCR1, XINTM, FRM);
	MCBSP_FSETS(RCR1, RWDLEN1, 32BIT);
	MCBSP_FSETS(XCR1, XWDLEN1, 32BIT);

	// set codec sampling frequency
	DSK6713_AIC23_setFreq(hCodec, DSK6713_AIC23_FREQ_44KHZ);

	// interrupt setup
	IRQ_globalDisable();			        // Globally disables interrupts
	IRQ_nmiEnable();				        // Enables the NMI interrupt
	IRQ_map(IRQ_EVT_RINT1,15);		// Maps an event to a physical interrupt
	IRQ_enable(IRQ_EVT_RINT1);		// Enables the event
	IRQ_globalEnable();				// Globally enables interrupts

	Uint8 frame_status = 0;
	Uint16 pin=0, pout=0;
	Uint16 i=0;

	tw_genr2fft(coeffs, wlen);
	bit_rev(coeffs, wlen>>1);

	// Wait until the first frame will be ready to process
	while(frame_status != 4){
		frame_status += frame_ready_flag;
		frame_ready_flag = 0;
	}

	while(1)
	{
		if (frame_ready_flag == 1){
			frame_ready_flag = 0;

			for (i=0; i<1024; i++){
				fft_in[2*i]   = buffer_in[(i+pin)%1280];
				fft_in[2*i+1] = 0;
			}
			DSPF_sp_cfftr2_dit(fft_in, coeffs, wlen);
			bit_rev(fft_in, wlen);

			pin += 256;
		}
	}
}

interrupt void serialPortRcvISR()
{
	union {Uint32 combo; short channel[2];} temp;

	temp.combo = MCBSP_read(DSK6713_AIC23_DATAHANDLE);

	buffer_in[j] = (float)temp.channel[0];
	j++;
	// Set frame_ready_flag to 1 if the next frame is ready
	if (j%256 == 0){
		frame_ready_flag = 1;
	}
	// Clear circular buffer index
	if (j == 1280){
		j = 0;
	}

	MCBSP_write(DSK6713_AIC23_DATAHANDLE, temp.combo);
}

Could you please point me what could be a reason of that?