Compiler/TM4C123GH6PM: fix_fft on TM4C123GH6PM

Tool/software: TI C/C++ Compiler

I am trying to implement the fix_fft algorithm , most specifically fix_fftr by Tom Roberts on the Tiva launchpad but I'm having trouble getting the correct outputs... See code below

#include <stdbool.h>//
#include <stdio.h>
#include <stdint.h>//
#include <float.h>
#include "inc/hw_memmap.h"//
#include "driverlib/debug.h"
#include "driverlib/gpio.h"//
#include "driverlib/rom.h"
#include "driverlib/sysctl.h"//
#include "driverlib/pin_map.h"
#include "driverlib/ssi.h"
#include "driverlib/pwm.h"
#include "driverlib/pwm.c"
#include "driverlib/adc.h"
#include "driverlib/adc.c"
#include "fix_fft.h"

///////////////Register definitions//////////////////////////////////
#define GPIO_PORTF_DATA_R       (*((volatile unsigned long *)0x400253FC))
#define GPIO_PORTF_DIR_R        (*((volatile unsigned long *)0x40025400))
#define GPIO_PORTF_AFSEL_R      (*((volatile unsigned long *)0x40025420))
#define GPIO_PORTF_PUR_R        (*((volatile unsigned long *)0x40025510))
#define GPIO_PORTF_DEN_R        (*((volatile unsigned long *)0x4002551C))
#define GPIO_PORTF_LOCK_R       (*((volatile unsigned long *)0x40025520))
#define GPIO_PORTF_CR_R         (*((volatile unsigned long *)0x40025524))
#define GPIO_PORTF_AMSEL_R      (*((volatile unsigned long *)0x40025528))
#define GPIO_PORTF_PCTL_R       (*((volatile unsigned long *)0x4002552C))
#define SYSCTL_RCGC2_R          (*((volatile unsigned long *)0x400FE108))
#define GPIO_PORTF_PDR_R        (*((volatile unsigned long *)0x40025514))
///////////////
#define GPIO_PORTA_AMSEL_R (*((volatile unsigned long *)0x40004528))
#define GPIO_PORTA_PCTL_R (*((volatile unsigned long *)0x4000452C))
#define GPIO_PORTA_DIR_R        (*((volatile unsigned long *)0x40004400))
#define GPIO_PORTA_AFSEL_R (*((volatile unsigned long *)0x40004420))
#define GPIO_PORTA_DEN_R (*((volatile unsigned long *)0x4000451C))




*/

////////////////////////////////////////////////////////////////////////

#define true 1
#define false 0

#define GPIO_PORTF_LOCK_R       (*((volatile unsigned long *)0x40025520))
/*

void PWM_RGB_Init(void);
void ADC0_Init(void);
void UnlockPortF(void);
unsigned int ADC_CH0_Sample(void);
//enum color{red,blue,green};
unsigned int Green_ColorTempConvert(unsigned int ADCValue);
unsigned int Blue_ColorTempConvert(unsigned int ADCValue);
unsigned int Red_ColorTempConvert(unsigned int ADCValue);
void processOnTimes(unsigned int* redAddress,unsigned int* blueAddress, unsigned int* greenAddress);
void PF0Pushbutton_Init(void);

*/
short sine20[128]={0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281,-755,-989,-909,-540,0,541,910,990,756,282,-281};
short sine40[128]={0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909,755,-282,-990,-541,540,989,281,-756,-910,-1,0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909,755,-282,-990,-541,540,989,281,-756,-910,-1,0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909,755,-282,-990,-541,540,989,281,-756,-910,-1,0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909,755,-282,-990,-541,540,989,281,-756,-910,-1,0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909,755,-282,-990,-541,540,989,281,-756,-910,-1,0,909,755,-282,-990,-541,540,989,281,-756,-910,-1,909};
short cosine22[128]={1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310,309,809,1000,809,309,-310,-810,-1000,-810,-310};
volatile long FFT_power[64];
int FFT_result[128];



int
main(void)
{

//Fix_FFT Attempt
//fix_fftr(short f[], int m, int inverse)
//Notes: N(number of samples)=2^m, therefore if I want 128, log2(128)=7 so m =7

	int i;
	fix_fftr(cosine22, 7, 0);
    volatile long max=0;
    volatile int maxIndex=0;

    for(i=0;i<64;i++){
    	//capture Power^2
    	FFT_power[i]=((long)cosine22[i]*(long)cosine22[i])+((long)cosine22[i+64]*(long)cosine22[i+64]);
    	//capture max
    	if(FFT_power[i]>max){
    		max=FFT_power[i];
    		maxIndex=i;
    	}
    }


    return(0);

}

My understanding of fix_fftr is that it as arguments are:

1. An array of size N (in my case 128)

2. An "m" factor which is just log2(N) which in my case is 7

3. A flag that tells the function whether I want forward or reverse FFT, in my case should be 0.

And that it simply replaces the array you input with an array containing N/2 real elements (at indices 0 to N/2-1) l and N/2 imaginary elements (at indices N/2 to N).

I started by inserting a cosine function and trying to get back a spike at the frequency of choice. My sampling frequency is 220Hz and the frequency of the wave I am trying to capture is 22Hz. Then, I tried to capture the relative power in each frequency bin (I know you're supposed to sqrt for true power but I skipped that part, sue me). Based on my input in the time domain which is 1/10 the sampling frequency, one would expect the N/10th bin to have the largest peak. However when I run in debug and check my numbers I get a drastically different result than what we expect with strange spikes at various locations:

Needless to say I'm a little stumped right now. If anyone has any tips about fftr or what I'm doing wrong, I'd appreciate it.

Cheers,

Jim