AudioTimerAVR.h

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#pragma once
 
#ifdef __AVR__
#include "AudioTools/CoreAudio/AudioTimer/AudioTimerBase.h"
 
namespace audio_tools {
typedef void (*repeating_timer_callback_t)(void* obj);
class AudioTimerDriverAVR;
static AudioTimerDriverAVR* timerAlarmRepeatingRef = nullptr;
 
class AudioTimerDriverAVR : public AudioTimerDriverBase {
 public:
  AudioTimerDriverAVR() { timerAlarmRepeatingRef = this; }
 
  bool begin(repeating_timer_callback_t callback_f, uint32_t time,
             TimeUnit unit = MS) override {
    callback = callback_f;
 
    // we determine the time in microseconds
    uint32_t timeUs = 0;
    switch (unit) {
      case MS:
        timeUs = time * 1000;
        break;
      case US:
        timeUs = time;
        break;
      case HZ:
        // convert hz to time in us
        timeUs = AudioTime::toTimeUs(time);
        break;
    }
    // frequency = beats / second
    setupTimer(1000000 / time);
    return true;
  }
 
  // ends the timer and if necessary the task
  bool end() override {
    TRACED();
    noInterrupts();
    // end timer callback
    TCCR1B = 0;
    interrupts();  // enable all interrupts
    return true;
  }
 
  static void tickerCallback() {
    if (timerAlarmRepeatingRef != nullptr &&
        timerAlarmRepeatingRef->callback != nullptr)
      timerAlarmRepeatingRef->callback(timerAlarmRepeatingRef);
  }
 
 protected:
  repeating_timer_callback_t callback = nullptr;
 
  void setupTimer(uint64_t sample_rate) {
    TRACED();
    // CPU Frequency 16 MHz
    // prescaler 1, 256 or 1024 => no prescaling
    uint32_t steps = F_CPU / 8 / sample_rate;  // e.g. (16000000/8/44100=>45)
    if (steps > 65535) {
      LOGE("requested sample rate not supported: %d - we use %d", sample_rate,
           F_CPU / 65536);
      steps = 65535;
    } else {
      LOGD("compare match register set to %d", steps);
    }
 
    // setup timer intterupt
    noInterrupts();
    TCCR1B = 0;
    // compare match register
    OCR1A = steps;
    TCCR1B |= (1 << WGM12);  // CTC mode
    // TCCR1B |= (1 << CS10); // prescaler 1
    TCCR1B |= (1 << CS11);    // prescaler 8
    TIMSK1 |= (1 << OCIE1A);  // enable timer compare interrupt
    interrupts();             // enable all interrupts
  }
};
 
using AudioTimerDriver = AudioTimerDriverAVR;
 
}  // namespace audio_tools
 
#endif