/*
This is a slightly modified version of the timer setup found at:
https://github.com/maxbader/arduino_tools
*/
void startTimer(int frequencyHz) {
REG_GCLK_CLKCTRL = (uint16_t) (GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK0 | GCLK_CLKCTRL_ID (GCM_TCC2_TC3)) ;
while ( GCLK->STATUS.bit.SYNCBUSY == 1 );
TcCount16* TC = (TcCount16*) TC3;
TC->CTRLA.reg &= ~TC_CTRLA_ENABLE;
// Use the 16-bit timer
TC->CTRLA.reg |= TC_CTRLA_MODE_COUNT16;
while (TC->STATUS.bit.SYNCBUSY == 1);
// Use match mode so that the timer counter resets when the count matches the compare register
TC->CTRLA.reg |= TC_CTRLA_WAVEGEN_MFRQ;
while (TC->STATUS.bit.SYNCBUSY == 1);
// Set prescaler to 1024
TC->CTRLA.reg |= TC_CTRLA_PRESCALER_DIV1024;
while (TC->STATUS.bit.SYNCBUSY == 1);
setTimerFrequency(frequencyHz);
// Enable the compare interrupt
TC->INTENSET.reg = 0;
TC->INTENSET.bit.MC0 = 1;
NVIC_EnableIRQ(TC3_IRQn);
TC->CTRLA.reg |= TC_CTRLA_ENABLE;
while (TC->STATUS.bit.SYNCBUSY == 1);
}
void loop() {
int newPotValue = analogRead(POT_PIN);
// We only want to update the frequency if there has been significant changes
// to the potentiometer. We do this to prevent jitters but also to make this
// loop more efficient.
if (abs(newPotValue - potValue) > POT_JITTER_THRESHOLD) {
potValue = newPotValue;
setTimerFrequency(frequencyFromPotValue(potValue));
}
}
void setTimerPairFrequency(Timer timerA, Timer timerB, uint16_t herz) {
// The timer A value dictates the frequency for both timer A and B.
// Set a higher frequency for timer B so that interrupts are not fired the same time.
setTimerFrequency(timerA, TIMER_PRESCALER, herz);
setTimerFrequency(timerB, TIMER_PRESCALER, herz);
}
