MHZ19PWM.h

#pragma once
#include <Arduino.h>

#if defined(ARDUINO_ARCH_ESP8266)
#define ISR_ATTR ICACHE_RAM_ATTR
#elif defined(ARDUINO_ARCH_ESP32)
#define ISR_ATTR IRAM_ATTR
#else
#define ISR_ATTR
#endif

enum MHZ_MODE {
	MHZ_CONTINUOUS_MODE,
	MHZ_DELAYED_MODE,
	MHZ_ASYNC_MODE
};

class MHZ19PWM
{
public:
	static MHZ19PWM * instance;
	static void ISR_ATTR isr();

	MHZ19PWM(byte pin, MHZ_MODE mode = MHZ_DELAYED_MODE);
	~MHZ19PWM();
	void useLimit(unsigned int value);
	float getCO2();
	void requestData();
	bool isDataReady();
private:
	MHZ_MODE _mode;
	byte _pin;
	unsigned int _limit = 5000;
	bool _attached = false;
	volatile bool _skipLow = false;
	volatile float _currentValue = 0;
	unsigned long _startHigh = 0;
	unsigned long _startLow = 0;
	float _timeHigh = 0;
	float _timeLow = 0;

	void start();
	void stop();
	void waitForData();
	void ISR_ATTR isrInternal();
};