Respect tone()'s minimum frequency (issue #14)

CHANGELOG.md

@@ -1,6 +1,11 @@
 ContinuousStepper: changelog
 ============================
 
+HEAD
+-----
+
+* Respect `tone()`'s minimum frequency (issue #14)
+
 3.0.1
 -----
 

src/ContinuousStepper/Tickers/AnalogWriteFrequency.hpp

@@ -24,6 +24,12 @@ class AwfOscillator {
     active_ = false;
   }
 
+  unsigned int minFrequency() const {
+    // The analogWriteFrequency function has a lower limit of a few Hz.
+    // https://www.pjrc.com/teensy/td_pulse.html#frequency
+    return 5;
+  }
+
 private:
   bool active_ = false;
   uint8_t pin_ = nullPin;

src/ContinuousStepper/Tickers/KhoiH_PWM.hpp

@@ -24,6 +24,10 @@ class KhoihOscillator {
     pwm_->setPWM(pin_, 500, 0);
   }
 
+  unsigned int minFrequency() const {
+    return 1;
+  }
+
 private:
   uint8_t pin_ = nullPin;
   KhoiH_PWM *pwm_ = nullptr;

src/ContinuousStepper/Tickers/OscillatorTicker.hpp

@@ -33,8 +33,9 @@ class OscillatorTicker : StepperTicker {
   }
 
   void setPeriod(unsigned long period) {
-    if (period) {
-      oscillator_.start(1e6 / period);
+    auto frequency = period ? 1e6 / period : 0;
+    if (frequency >= oscillator_.minFrequency()) {
+      oscillator_.start(frequency);
     } else {
       oscillator_.stop();
     }

src/ContinuousStepper/Tickers/Tone.hpp

@@ -19,6 +19,20 @@ class ToneOscillator {
     noTone(pin_);
   }
 
+  unsigned int minFrequency() const {
+#if defined(ARDUINO_ARCH_AVR)
+    // It is not possible to generate tones lower than 31Hz
+    // https://www.arduino.cc/reference/en/language/functions/advanced-io/tone/
+    return 31;
+#elif defined(ARDUINO_ARCH_NRF52)
+    // For the nRF52, the allowed range for parameter `frequency` is `[20..25000]`.
+    // https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/1.5.0/cores/nRF5/Tone.h#L54
+    return 20;
+#else
+    return 1;
+#endif
+  }
+
 private:
   uint8_t pin_ = nullPin;
 };