//************************************************
//  BMP085 Barometric Pressure Sensor
//
//  - Datasheet: http://www.bosch-sensortec.com/content/language1/downloads/BST-BMP085-DS000-05.pdf
//
//  - Written in CCS PCH C using floating point math
//  - Several integer math versions of this driver exist but the speed improvement is
//    not warranted in typical weather station type applications
// 
//  - Based on a paper posted to thebackshed.com by DuinoMiteMegaAn
//    http://www.thebackshed.com/forum/forum_posts.asp?TID=4768&PN=9 
//
//  - Usage:
//     Call once: bmp085Calibration();
//     P_mBar_float = BMP085Pressure(true);  //  calls for temperature first
//     P_mBar_float = BMP085Pressure(false);  // skips temperature reading, assumes done previously
//     T_Cent_float = BMP085Temperature();
//     t_reading = _Temp;  _Temp set on every temperature reading
//        Note:   pressure reading is temp compensated so call for temp reading prior to pressure reading periodically or on each reading
//
//  Al Testani
//  08/17/12
//************************************************

// place a #use i2c statement in the main program and comment this out if not applicable
//#use i2c(master, sda=PIN_C4, scl=PIN_C3, FAST, FORCE_HW)

#include <math.h>

const int8 OVS_S = 3; // Oversampling Setting (0,1,2,3 from ultra low power, to ultra hi-resolution)

#define BMP085_ADDRESS 0xEE          // I2C address of BMP085
#define P_CORRECTION   32           // in mBars - factor to adjust for elevation to match local weather station pressure
                                     // this value for 275m above sea level (in Cortina, Mieres, Asturias)


// Calibration values
signed int16 ac1;
signed int16 ac2;
signed int16 ac3;
int16 ac4;
int16 ac5;
int16 ac6;
signed int16 b1;
signed int16 b2;
signed int16 mb;
signed int16 mc;
signed int16 md;

// floating point cal factors
float _c3;
float _c4;
float _b1;
float _c5;
float _c6;
float _mc;
float _md;

// polynomomial constants
float _x0;
float _x1;
float _x2;
float _y0;
float _y1;
float _y2;
float _p0;
float _p1;
float _p2;

float _s;     // T-25, used in pressure calculation - must run temperature reading before pressure reading
float _Temp;  // set after every temperature or temperature/pressure reading


//----------------------------------------------
int8 BMP085ReadByte(int8 address)
//----------------------------------------------
{
int8 data;

   i2c_start();
   i2c_write(BMP085_ADDRESS);
   i2c_write(address);
   i2c_start();
   i2c_write(BMP085_ADDRESS | 0x01 );
   data=i2c_read(0);
   i2c_stop();
   return(data);
}


//----------------------------------------------
int16 BMP085ReadInt(int8 address)
//----------------------------------------------
{
int8 msb, lsb;
int16 temp;

   i2c_start();
   i2c_write(BMP085_ADDRESS);
   i2c_write(address);
   i2c_start();
   i2c_write(BMP085_ADDRESS | 0x01 );
   msb = i2c_read();
   lsb = i2c_read(0);
   i2c_stop();
   temp = make16(msb, lsb);
   return ( temp );
}


//----------------------------------------------
void BMP085WriteByte(int8 address, int8 data)
//----------------------------------------------
{
   i2c_start();
   i2c_write(BMP085_ADDRESS);
   i2c_write(address);
   i2c_write(data);
   i2c_stop();
}




    // calculate floating point cal factors
   _c3 = 0.0048828125 * ac3;            // 160 * pow2(-15) * ac3;
   _c4 = 0.000000030517578125 * ac4;    // 1E-3 * pow2(-15) * ac4;
   _c5 = 0.00000019073486328125 * ac5;  // (pow2(-15)/160) * ac5;
   _c6 = (float)ac6;
   _b1 = 0.00002384185791015625 * b1;   // 25600 * pow2(-30) * b1;
   _mc = 0.08 * mc;                     // (pow2(11) / 25600) * mc;
   _md = (float)md / 160;
   
   // calculate polynomial constants
   _x0 = (float)ac1;
   _x1 = 0.01953125 * ac2;             // 160 * pow2(-13) * ac2;
   _x2 = 0.000762939453125 * b2;       // 25600 * pow2(-25) * b2;
   _y0 = _c4 * 32768;                  //_c4 * pow2(15);
   _y1 = _c4 * _c3;
   _y2 = _c4 * _b1;
   _p0 = 2.364375; 
   _p1 = 0.992984;
   _p2 = 0.000004421;   
}


// Read the uncompensated temperature value
//----------------------------------------------
int16 BMP085ReadUT()
//----------------------------------------------
{
int16 ut;
 
  // Write 0x2E into Register 0xF4
  BMP085WriteByte(0xF4, 0x2E);
  delay_ms(5); // Wait at least 4.5ms
  // Read two bytes from registers 0xF6 and 0xF7
  ut = BMP085ReadInt(0xF6);
  return((float)ut);
}


// Read the uncompensated pressure value
//----------------------------------------------
int32 bmp085ReadUP()
//----------------------------------------------
{
int8 msb, lsb, xlsb;
float p;
 
  // Write 0x34+(OSS<<6) into register 0xF4
  // Request a pressure reading w/ oversampling setting
  BMP085WriteByte(0xF4, (0x34 + (OVS_S<<6)) );
 
  // Wait for conversion, delay time dependent on OSS
  switch (OVS_S)
  {
     case 0: delay_ms(5);  break;
     case 1: delay_ms(8);  break;
     case 2: delay_ms(14); break;
     case 3: delay_ms(26); break;
  }   
 
  // Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)
   msb  = BMP085ReadByte(0xF6);
   lsb  = BMP085ReadByte(0xF7);
   xlsb = BMP085ReadByte(0xF8);
   p = (256*msb) + lsb + (xlsb/256);
   return(p);
}


//----------------------------------------------
float BMP085GetTemp(float _tu)
//----------------------------------------------
{
float alpha, T;

   alpha = _c5 * (_tu - _c6);
   T = alpha + (_mc/(alpha + _md));
   _s = T - 25;
   return(T);
}   


//----------------------------------------------
float BMP085GetPressure(float _pu)
//----------------------------------------------
{
float x, y, z;
float P;

   x = _x2*_s*_s + _x1*_s + _x0;
   y = _y2*_s*_s + _y1*_s + _y0;
   z = ((float)_pu - x) / y;
   P = _p2*z*z + _p1*z + _p0;
   P += P_CORRECTION;
   return(P);
}


//----------------------------------------------
float BMP085Pressure(boolean getTemp)
//----------------------------------------------
{
   if (getTemp)
      _Temp = BMP085GetTemp(BMP085ReadUT());  // creates _s required for pressure calculation
   return(BMP085GetPressure(BMP085ReadUP()));
}


//----------------------------------------------
float BMP085Temperature(void)
//----------------------------------------------
{
   _Temp = BMP085GetTemp(BMP085ReadUT());
   return(_Temp);
}