[avr-gcc-list] Troubles with ADC on ATMega16

[Olav Torheim]

Hi!

 

I have a little problem with creating a real time system on my AVR ATMega 16. The response time for my system is 60 us and I need to alway have digitized data ready from four analogue channels.

 

What I am trying to do is to create a program that is running through a loop, sampling four channels, one after another. My program is running fine when only sampling one channel. But when I try to sequencially sample through four channels, I am not able to get a stable result from any conversion. It seems like the program is not able to handle the switching between the channels. Does anybody understand why?

 

Olav Torheim

 

--

 

Cut and paste from my main program:

 

startADC(channelcounter+4); // Starting first AD conversion

while(1)
{
                                if (gAdcConversionCompleted == 1)
                                {

                                        mL[channelcounter] = returnAILow();
                                        mH[channelcounter] = returnAIHigh();

 

// If I comment away this if-statement, the program is running fine while

//only following one channel! :

 

                                        if (channelcounter == 3)
                                        {
                                                channelcounter = 0;
                                        }
                                        else
                                        {
                                                channelcounter++;
                                        }

                                        startADC(channelcounter+4); // Starting next conversion

                                }
}

 

Source code for ADC_AVR.C:

 

#include <io.h>
#include <interrupt.h>
#include <sig-avr.h>

#ifndef ADC_AVR
#define ADC_AVR

volatile int gAdcConversionCompleted;

char mAiLow, mAiHigh;

SIGNAL(SIG_ADC)
{
        gAdcConversionCompleted = 1;
}

void initAI(void)
{
  outp(0x0F, DDRA);
        sbi(ADCSR, ADEN); // Slær på AD-umsetjaren
        sbi(ADCSR, ADIE); // Slær på Interrupt-Enable (IE)
}

void convertADC(char channel)
{
        outp(channel, ADMUX); // Vel kanal
  

        sbi(ADCSR, ADSC); // Startar AD-umsetjing
        while(gAdcConversionCompleted!=1);
        gAdcConversionCompleted =0;

        mAiLow = inp(ADCL);
        mAiHigh = inp(ADCH);
}

void startADC(char channel)
{
  
        outp(channel, ADMUX); // Vel kanal
  gAdcConversionCompleted =0;
  outp(0x00, ADCL);
  outp(0x00,ADCH); 
        sbi(ADCSR, ADSC); // Startar AD-umsetjing
       
}

char returnAILow(void)
{
 return inp(ADCL);
}

char returnAIHigh(void)
{
 return inp(ADCH);
}

char readAIHigh(void)
{
        return mAiHigh;
}

char readAILow(void)
{
        return mAiLow;
}

#endif

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