PWM+ADC+Atmega128+FreeRTOS problem.

anonymous wrote on Sunday, November 15, 2009:


I have strange problems with those four. I have my PWM on timer3, when I initialize it all readings queued by ADC reading functions go wrong. My PWM initialization:

    void initPwm (){ 
        TCNT3 = 0;
    OCR3A = 0;
    OCR3B = 0;
    TCCR3A = _BV(COM3A1)| _BV(COM3B1)| _BV(WGM31)|_BV(WGM30);
    TCCR3B = _BV(CS30);

Next one of my ADC readings tasks(chanell 0):

    void ADC0(void* pvParameters)
    uint8_t odczyt;
    //ADC0 - czujnik - 0
    ADMUX &= ~(_BV(MUX4) |_BV(MUX3) |_BV(MUX2) |_BV(MUX1) |_BV(MUX0));
    ADCSRA |= _BV(ADSC);  
    odczyt = ADCH;  
    xQueueSendToBack(xQueue0, &odczyt, 0);

And ADC initialization:

      void initAdc (){

    ADMUX &= ~_BV(REFS1);
    ADMUX |= _BV(REFS0);  
    ADMUX |= _BV(ADLAR);

Task creation:


And so on… Lcd task try to read and if, show on LCD. Problem is that if I initPwm() there are problems - for example form 2 ADC channels I get simmilar readings, and when I changes value ewerything stops… Hard to say whats going on because its totally random! The code without FreeRTOS works perfectly, but I must use this RTOS…

Please help me, I spent few weaks on it ant can’t manage to figure it out. I can post somewhere full code if somebody wants to help me.

Thanks in advance.

davedoors wrote on Monday, November 16, 2009:

Not sure I can really help, don’t know about AVR specifics, but it looks like your ADC0() task is polling the ADC. If this task is not the lowest priority task then no tasks of lower priority will ever run. It would be best to make it event driven so it only runs when there is an adc reading to process.

anonymous wrote on Tuesday, November 17, 2009:

Thank you for your reply. It might be better, I don’t have lower priority tasks, but for future. Do u know how I should fix it?