DHT.hh

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#ifndef COSA_DHT_HH
#define COSA_DHT_HH

#include "Cosa/Types.h"
#include "Cosa/ExternalInterrupt.hh"
#include "Cosa/IOStream.hh"

class DHT : public ExternalInterrupt {
public:
  static const int16_t INIT_HUMIDITY_SAMPLE = 1000;

  static const int16_t INIT_TEMPERATURE_SAMPLE = 850;

  DHT(Board::ExternalInterruptPin pin = Board::EXT0) :
    ExternalInterrupt(pin, ExternalInterrupt::ON_FALLING_MODE),
    m_state(INIT),
    m_start(0),
    m_value(0),
    m_bits(0),
    m_ix(0),
    m_humidity(INIT_HUMIDITY_SAMPLE),
    m_temperature(INIT_TEMPERATURE_SAMPLE)
  {}

  int16_t humidity() const
  {
    return (m_humidity);
  }

  int16_t temperature() const
  {
    return (m_temperature);
  }

  bool sample_request();

  bool sample_await();

  bool sample()
    __attribute__((always_inline))
  {
    return (sample_request() && sample_await());
  }

  bool sample(int16_t& humidity, int16_t& temperature)
    __attribute__((always_inline))
  {
    bool res = sample();
    humidity = m_humidity;
    temperature = m_temperature;
    return (res);
  }

protected:
  virtual void on_interrupt(uint16_t arg = 0);

  virtual void on_sample_completed(bool valid)
  {
    UNUSED(valid);
  }

  bool is_valid();

  virtual void adjust_data() = 0;

  // States
  enum {
    INIT,                       
    IDLE,                       
    REQUEST,                    
    RESPONSE,                   
    SAMPLING,                   
    COMPLETED                   
  } __attribute__((packed));

  static const uint16_t MIN_PERIOD = 2048;

  static const uint16_t LOW_THRESHOLD = 50;
  static const uint16_t BIT_THRESHOLD = 100;
  static const uint16_t HIGH_THRESHOLD = 200;

  static const uint8_t DATA_MAX = 5;

  static const uint8_t DATA_LAST = DATA_MAX - 1;

  union data_t {
    uint8_t as_byte[DATA_MAX];
    struct {
      int16_t humidity;
      int16_t temperature;
      uint8_t chksum;
    };
  };

  volatile uint8_t m_state;

  uint16_t m_start;

  uint8_t m_value;

  uint8_t m_bits;

  uint8_t m_ix;

  data_t m_data;

  /* Latest valid humidity reading. */
  int16_t m_humidity;

  /* Latest valid temperature reading. */
  int16_t m_temperature;

  friend IOStream& operator<<(IOStream& outs, DHT& dht);
};

class DHT11 : public DHT {
public:
  DHT11(Board::ExternalInterruptPin pin = Board::EXT0) :
    DHT(pin)
  {
  }

protected:
  virtual void adjust_data();
};

class DHT22 : public DHT {
public:
  DHT22(Board::ExternalInterruptPin pin = Board::EXT0) :
    DHT(pin)
  {
  }

protected:
  virtual void adjust_data();
};
#endif