//
//    FILE: dht.cpp
//  AUTHOR: Rob Tillaart
// VERSION: 0.1.07
// PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
//     URL: http://arduino.cc/playground/Main/DHTLib
//
// HISTORY:
// 0.1.07 added support for DHT21
// 0.1.06 minimize footprint (2012-12-27)
// 0.1.05 fixed negative temperature bug (thanks to Roseman)
// 0.1.04 improved readability of code using DHTLIB_OK in code
// 0.1.03 added error values for temp and humidity when read failed
// 0.1.02 added error codes
// 0.1.01 added support for Arduino 1.0, fixed typos (31/12/2011)
// 0.1.0 by Rob Tillaart (01/04/2011)
//
// inspired by DHT11 library
//
// Released to the public domain
//

#include "dht.h"

#define TIMEOUT (F_CPU/1600)    // unsigned int in code, for higher CPU speeds this might exceed MAXINT.

/////////////////////////////////////////////////////
//
// PUBLIC
//

// return values:
// DHTLIB_OK
// DHTLIB_ERROR_CHECKSUM
// DHTLIB_ERROR_TIMEOUT
int dht::read11(uint8_t pin)
{
	// READ VALUES
	int rv = read(pin);
	if (rv != DHTLIB_OK)
    {
		humidity    = DHTLIB_INVALID_VALUE; // invalid value, or is NaN prefered?
		temperature = DHTLIB_INVALID_VALUE; // invalid value
		return rv;
	}

	// CONVERT AND STORE
	humidity    = bits[0];  // bit[1] == 0;
	temperature = bits[2];  // bits[3] == 0;

	// TEST CHECKSUM
	// bits[1] && bits[3] both 0
	uint8_t sum = bits[0] + bits[2];
	if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;

	return DHTLIB_OK;
}

// return values:
// DHTLIB_OK
// DHTLIB_ERROR_CHECKSUM
// DHTLIB_ERROR_TIMEOUT
int dht::read21(uint8_t pin)
{
        return read22(pin);  // dataformat identical to DHT22
}

// return values:
// DHTLIB_OK
// DHTLIB_ERROR_CHECKSUM
// DHTLIB_ERROR_TIMEOUT
int dht::read22(uint8_t pin)
{
	// READ VALUES
	int rv = read(pin);
	if (rv != DHTLIB_OK)
    {
		humidity    = DHTLIB_INVALID_VALUE;  // invalid value, or is NaN prefered?
		temperature = DHTLIB_INVALID_VALUE;  // invalid value
		return rv; // propagate error value
	}

	// CONVERT AND STORE
	humidity = word(bits[0], bits[1]) * 0.1;

	if (bits[2] & 0x80) // negative temperature
	{
		temperature = -0.1 * word(bits[2] & 0x7F, bits[3]);
	}
	else
	{
		temperature = 0.1 * word(bits[2], bits[3]);
	}

	// TEST CHECKSUM
	uint8_t sum = bits[0] + bits[1] + bits[2] + bits[3];
	if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;

	return DHTLIB_OK;
}

/////////////////////////////////////////////////////
//
// PRIVATE
//

// return values:
// DHTLIB_OK
// DHTLIB_ERROR_TIMEOUT
int dht::read(uint8_t pin)
{
	// INIT BUFFERVAR TO RECEIVE DATA
	uint8_t cnt = 7;
	uint8_t idx = 0;

	// EMPTY BUFFER
	for (uint8_t i=0; i< 5; i++) bits[i] = 0;

	// REQUEST SAMPLE
	pinMode(pin, OUTPUT);
	digitalWrite(pin, LOW);
	delay(20);
	digitalWrite(pin, HIGH);
	delayMicroseconds(40);
	pinMode(pin, INPUT);

	// GET ACKNOWLEDGE or TIMEOUT
	unsigned int loopCnt = TIMEOUT;
	while(digitalRead(pin) == LOW)
		if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

	loopCnt = TIMEOUT;
	while(digitalRead(pin) == HIGH)
		if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

	// READ THE OUTPUT - 40 BITS => 5 BYTES
	for (uint8_t i=0; i<40; i++)
	{
		loopCnt = TIMEOUT;
		while(digitalRead(pin) == LOW)
			if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

		unsigned long t = micros();

		loopCnt = TIMEOUT;
		while(digitalRead(pin) == HIGH)
			if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

		if ((micros() - t) > 40) bits[idx] |= (1 << cnt);
		if (cnt == 0)   // next byte?
		{
			cnt = 7;   
			idx++;      
		}
		else cnt--;
	}

	return DHTLIB_OK;
}
//
// END OF FILE
//