Timer_Counter.ino

//#define COUNT_CYCLES
#define SLOW_SAMPLE

// setup TC2 in capture mode - just use it to grab counter values
void TC2_setup() {
  PMC->PMC_PCER0 |= PMC_PCER0_PID29;  // TC2 power ON : Timer Counter 0 channel 2 IS TC2

//        TIMER_CLOCK1 Clock: internal MCK/2 clock signal (from PMC)
//        TIMER_CLOCK2 Clock: internal MCK/8 clock signal (from PMC)
//        TIMER_CLOCK3 Clock: internal MCK/32 clock signal (from PMC)
//        TIMER_CLOCK4 Clock: internal MCK/128 clock signal (from PMC)

  TC0->TC_CHANNEL[2].TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK2; //i.e., 42 MHz clock.
  TC0->TC_CHANNEL[2].TC_CCR = TC_CCR_SWTRG | TC_CCR_CLKEN;// Software trigger TC2 counter and enable
}

// setup TC3 in waveform mode - use it generate 25 us interrupts
void TC3_setup() {
  PMC->PMC_PCER0 |= PMC_PCER0_PID30;  // TC3 power ON : Timer Counter 1 channel 0 IS TC3
  TC1->TC_CHANNEL[0].TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK1   // MCK/2, clk on rising edge
                              | TC_CMR_WAVE                // Waveform mode
                              | TC_CMR_WAVSEL_UP_RC;       // UP mode with automatic trigger on RC Compare

  // e.g., an RC value of 42 cycles, a clock of 84MHz/2 = 42 MHz, the sampling frequency is 1 MHz
  #ifdef SLOW_SAMPLE
    TC1->TC_CHANNEL[0].TC_RC = 10500;  // Frequency = (Mck/2)/TC_RC = 4000 Hz
  #else 
    TC1->TC_CHANNEL[0].TC_RC = 1050;  // Frequency = (Mck/2)/TC_RC = 40,000 Hz
  #endif
  TC1->TC_CHANNEL[0].TC_IER = TC_IER_CPCS;
  TC1->TC_CHANNEL[0].TC_IDR = ~(TC_IER_CPCS);
  TC1->TC_CHANNEL[0].TC_CCR = TC_CCR_SWTRG | TC_CCR_CLKEN;// reset counter and enable clock
}

void ADC_setup(){
  PMC->PMC_PCER1  |= PMC_PCER1_PID37;             // ADC power on
  ADC->ADC_CHER    = ADC_CHER_CH7 | ADC_CHER_CH6; // enable A0 (ch7) and A1 (ch6)
  ADC->ADC_MR     |= ADC_MR_TRANSFER(0)           // Transfer Period = (TRANSFER * 2 + 3) ADCClock periods
                  |  ADC_MR_PRESCAL(1)            // ADCClock = MCK / ( (PRESCAL+1) * 2 ). clock = 21 MHz
                  |  ADC_MR_LOWRES                // 1 = 10 bit sample, 0 = 12 bit sample
                  |  ADC_MR_FREERUN;              // freerun mode. 
  ADC->ADC_ACR     = ADC_ACR_IBCTL(0b01);         // For frequency > 500 KHz
  ADC->ADC_CR      = ADC_CR_START | ADC_CR_SWRST; // Reset ADC and start conversion
}

void setup(){
  Serial.begin(115200);
  
  #ifdef COUNT_CYCLES
    TC2_setup(); //if we're just counting how many cycles ADC takes
  #else
    ADC_setup(); //otherwise we're performing precision timed ADCs
    TC3_setup(); 
  #endif
}

void loop(){

  #ifdef COUNT_CYCLES
    TC0->TC_CHANNEL[2].TC_CCR |= TC_CCR_SWTRG; //software trigger to reset the counter
  #endif

  // perform ADC, and transmit value
    Serial.println(analogRead(A0), DEC); //two channel readings take 5371 cycles
//    Serial.println(analogRead(A1), DEC);

  // measure time taken to perform ADC and transmit value
    #ifdef COUNT_CYCLES
      uint32_t Time = TC0->TC_CHANNEL[2].TC_CV; //grab the counter value in real time
      Serial.print("Time: ");
      Serial.println(Time, DEC);
    #endif
    
  // wait for RC value to be reached, reading clears this flag in TC_SR
  #ifndef COUNT_CYCLES
    while(TC1->TC_CHANNEL[0].TC_SR & TC_SR_CPCS == 0){}
  #endif
}