问我使用ATmega164的CodeVisionAVR吉他调谐器代码不能处理超过4个样本

EN

#define M_PI 3.1415926f
#define N 4

unsigned char read_adc(void)
{
ADCSRA |= 0b01000000;  //start conversion;
while (ADCSRA&(0b01000000)); //wait conversion end
return ADCH;
}

float computeDft()
{      
    unsigned char x[N] = {0};
    float max = 0;   
    float maxi = 0;
    float magnitude = 0; 
    int k = 0;
    int n = 0;
    float re = 0;
    float im = 0;          
    for (k = 0; k < N; k++)
    {       
        x[k] = read_adc();            
    }
    for (n = 0; n < N; n++)
    {
        for (k = 0; k < N; k++)
        {       
            re += x[k] * cos(n * k * M_PI / N);
            im -= x[k] * sin(n * k * M_PI / N);
        }
        magnitude = sqrt(re * re +  im * im);
        if (magnitude > maxi) 
        {
            maxi = magnitude;
            max = k;   
        }
    }                                     
    return max;   
}


/*
 * main function of program
 */
void main (void)
{          
float F = 0;
Init_initController();  // this must be the first "init" action/call!
#asm("sei")             // enable interrupts
// Crystal Oscillator division factor: 1
#pragma optsize-
CLKPR=0x80;
CLKPR=0x00;
#ifdef OPTIMIZE_SIZE
#pragma optsize+
#endif

TWCR=0x00;
//adc init
ADMUX = 0b10100111; // set ADC0
ADCSRA = 0b10000111; //set ADEN, precale by 128
while(TRUE)
{
    wdogtrig();         // call often else processor will reset
    F = computeDft();    
    L2 = 1;
    if(F > 20 && F < 100)
    {
        L3 = 1;
    }
}  


}// end main loop 

/* initialization file */

#include <mega164a.h>
#include "defs.h"


/*
 * most intialization values are generated using Code Wizard and depend on clock value
 */
void Init_initController(void)
{
// Crystal Oscillator division factor: 1
#pragma optsize-
CLKPR=0x80;
CLKPR=0x00;
#ifdef _OPTIMIZE_SIZE_
#pragma optsize+
#endif

// Input/Output Ports initialization
// Port A initialization
// Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In 
// State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=T 
PORTA=0x00;
DDRA=0x00;

// Port B initialization
PORTB=0x00;
DDRB=0x00;

// Port C initialization
PORTC=0x00;
DDRC=0x00;

// Port D initialization
PORTD=0b00100000; // D.5 needs pull-up resistor
DDRD= 0b01010000; // D.6 is LED, D.4 is test output

// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: Timer 0 Stopped
// Mode: Normal top=FFh
// OC0 output: Disconnected
TCCR0A=0x00;
TCCR0B=0x00;
TCNT0=0x00;
OCR0A=0x00;
OCR0B=0x00;

// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 19.531 kHz = CLOCK/256
// Mode: CTC top=OCR1A
// OC1A output: Discon.
// OC1B output: Discon.
// Noise Canceler: Off
// Input Capture on Falling Edge
// Timer 1 Overflow Interrupt: Off
// Input Capture Interrupt: Off
// Compare A Match Interrupt: On
// Compare B Match Interrupt: Off

TCCR1A=0x00;
TCCR1B=0x0D;
TCNT1H=0x00;
TCNT1L=0x00;
ICR1H=0x00;
ICR1L=0x00;

// 1 sec = 19531 counts = 4C41H counts, from 0 to 4C40 
// 4C40H = 4CH (MSB) and 40H (LSB)
OCR1AH=0x4C;
OCR1AL=0x40;

OCR1BH=0x00;
OCR1BL=0x00;

// Timer/Counter 2 initialization
// Clock source: System Clock
// Clock value: Timer2 Stopped
// Mode: Normal top=0xFF
// OC2A output: Disconnected
// OC2B output: Disconnected
ASSR=0x00;
TCCR2A=0x00;
TCCR2B=0x00;
TCNT2=0x00;
OCR2A=0x00;
OCR2B=0x00;

// External Interrupt(s) initialization
// INT0: Off
// INT1: Off
// INT2: Off
// Interrupt on any change on pins PCINT0-7: Off
// Interrupt on any change on pins PCINT8-15: Off
// Interrupt on any change on pins PCINT16-23: Off
// Interrupt on any change on pins PCINT24-31: Off
EICRA=0x00;
EIMSK=0x00;
PCICR=0x00;

// Timer/Counter 0,1,2 Interrupt(s) initialization
TIMSK0=0x00;
TIMSK1=0x02;
TIMSK2=0x00;

// USART0 initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART0 Receiver: On
// USART0 Transmitter: On
// USART0 Mode: Asynchronous
// USART0 Baud rate: 9600
UCSR0A=0x00;
UCSR0B=0xD8;
UCSR0C=0x06;
UBRR0H=0x00;
UBRR0L=0x81;

// USART1 initialization
// USART1 disabled
UCSR1B=0x00;


// Analog Comparator initialization
// Analog Comparator: Off
// Analog Comparator Input Capture by Timer/Counter 1: Off
ACSR=0x80;
ADCSRB=0x00;
DIDR1=0x00;

// Watchdog Timer initialization
// Watchdog Timer Prescaler: OSC/2048  
#pragma optsize-
#asm("wdr")
// Write 2 consecutive values to enable watchdog
// this is NOT a mistake !
WDTCSR=0x18;
WDTCSR=0x08;
#ifdef _OPTIMIZE_SIZE_
#pragma optsize+
#endif

}