#include <avr/io.h>
#define AD_CNT        3
#define AD_CLC        5
volatile uint16_t    ADBuf[AD_CNT][AD_CLC];
volatile uint16_t    ADSum[AD_CNT];
volatile uint8_t    src=0,ad_calc=0;

void init_adc(void) {
    uint8_t i,j;
    for (i=0;i<AD_CNT;i++) {
        for (j=0;j<AD_CLC;j++)
            ADBuf[i][j] = 0;
        ADSum[i] = 0;
    }
    ADCH = 0;
    ADCL = 0;
    ADMUX = _BV(REFS0);
    ADCSRA = _BV(ADEN) | _BV(ADPS2) | _BV(ADPS1) | _BV(ADSC);
}

int main(void) {
    PORTC = 0;
    DDRC = 0;

    ....

    init_adc();

    ....

    while(1) {        
        if (bit_is_clear(ADCSRA,ADSC)) {
            uint16_t ADres=ADC;
          

            ADSum[src] -= ADBuf[src][ad_calc];
            ADBuf[src][ad_calc] = ADres;        // Place new value into Buffer
            ADSum[src] += ADres;

            ad_calc++;
            ad_calc%=AD_CLC;
            if (!ad_calc) {
                src++;
                src%=AD_CNT;
                ADMUX = _BV(REFS0) | src;            
            }
            ADCSRA |= _BV(ADSC);
        }
        ....
    }
}

#define adcExtPow   6
#define adcEnter    5
#define adcUp       4
#define adcDn       3
#define adcEsc      2

#define ADCoff      ADCSR=0


unsigned int adc_values[7];
unsigned char adc_channel;
unsigned char adc_ready=0;


void InternalAdcInit(void)
{
  ADCSRA =
    (1 << ADEN) |  //ADC ON,
  //     ADSC     not start conversion
  //    ADATE     auto trigger disable
    (1 << ADIF) |  // clear conversion flag writing 1 to it
  //    ADIE     interrupt disable
    (1 << ADPS2) |   //prescaler =64 (ADPS2=1, ADPS1=1, ADPS0=0)
    (1 << ADPS1) |
  //    ADPS0
    0;

  ADMUX = //REFS1 |
    (1 << REFS0) |  // REFerence = AVCC with C on pin Vref (REFS1=0, REFS0=1)
//    (1 << ADLAR) |  // left adjust results - read high byte only
    0;
}


#define SetAdcChannel(mux) ADMUX = (0xE0 & ADMUX) | (mux)
#define StartAdcConversion() ADCSRA |= (1 << ADIF) | (1 << ADSC)
#define AdcConversionComplete (!(ADCSRA & (1 << ADSC)))

void InternalAdcService(void)
{
  static char adc_status;
    char my_adcl;

  switch (adc_status)
  {
  case 0:
    InternalAdcInit();
    SetAdcChannel(adc_channel = 0);
    StartAdcConversion();
    adc_status = 1;
    break;
  case 1:
    if (AdcConversionComplete)
    {    my_adcl=ADCL;
      adc_values[adc_channel] = (ADCH<<8) + my_adcl;
      if (++adc_channel >= COUNT_ELEMENTS(adc_values))
      {
        adc_channel = 0;
        adc_ready = 1;
      }
      SetAdcChannel(adc_channel);
      StartAdcConversion();
    }
    break;
  default:
    adc_status = 0;
  }
}