drivers/sensors/mpl115a2/mpl115a2.c

   1 /**************************************************************************/
   2 /*!
   3     @file     mpl115a2.c
   4     @author   K. Townsend (microBuilder.eu)
   5
   6     @brief    Drivers for the Freescale MPL115A2 I2C Digital Barometer
   7
   8     @section DESCRIPTION
   9
  10     The MPL115A2 is an I2C absolute pressure sensor, employing a MEMS
  11     pressure sensor with a conditioning IC to provide accurate pressure
  12     measurements from 50 to 115 kPa.
  13
  14     @section LICENSE
  15
  16     Software License Agreement (BSD License)
  17
  18     Copyright (c) 2012, K. Townsend
  19     All rights reserved.
  20
  21     Redistribution and use in source and binary forms, with or without
  22     modification, are permitted provided that the following conditions are met:
  23     1. Redistributions of source code must retain the above copyright
  24     notice, this list of conditions and the following disclaimer.
  25     2. Redistributions in binary form must reproduce the above copyright
  26     notice, this list of conditions and the following disclaimer in the
  27     documentation and/or other materials provided with the distribution.
  28     3. Neither the name of the copyright holders nor the
  29     names of its contributors may be used to endorse or promote products
  30     derived from this software without specific prior written permission.
  31
  32     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS ''AS IS'' AND ANY
  33     EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  34     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  35     DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
  36     DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  37     (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  38     LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  39     ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  40     (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  41     SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  42 */
  43 /**************************************************************************/
  44 #include "mpl115a2.h"
  45 #include "core/systick/systick.h"
  46
  47 extern volatile uint8_t   I2CMasterBuffer[I2C_BUFSIZE];
  48 extern volatile uint8_t   I2CSlaveBuffer[I2C_BUFSIZE];
  49 extern volatile uint32_t  I2CReadLength, I2CWriteLength;
  50
  51 static float _mpl115a2_a0;
  52 static float _mpl115a2_b1;
  53 static float _mpl115a2_b2;
  54 static float _mpl115a2_c12;
  55
  56 static bool _mpl115a2Initialised = false;
  57
  58 /**************************************************************************/
  59 /*!
  60     @brief  Reads an 8 bit value over I2C
  61 */
  62 /**************************************************************************/
  63 mpl115a2Error_t mpl115a2ReadPressureTemp(uint16_t *pressure, uint16_t *temp)
  64 {
  65   // Clear write buffers
  66   uint32_t i;
  67   for ( i = 0; i < I2C_BUFSIZE; i++ )
  68   {
  69     I2CMasterBuffer[i] = 0x00;
  70     I2CSlaveBuffer[i] = 0x00;
  71   }
  72
  73   I2CWriteLength = 3;
  74   I2CReadLength = 1;
  75   I2CMasterBuffer[0] = MPL115A2_ADDRESS;
  76   I2CMasterBuffer[1] = MPL115A2_REGISTER_STARTCONVERSION;
  77   I2CMasterBuffer[2] = 0x00;  // Why is this necessary to get results?
  78   i2cEngine();
  79
  80   // Wait a bit for the conversion to complete (3ms max)
  81   systickDelay(5);
  82
  83   I2CWriteLength = 2;
  84   I2CReadLength = 4;
  85   I2CMasterBuffer[0] = MPL115A2_ADDRESS;
  86   I2CMasterBuffer[1] = MPL115A2_REGISTER_PRESSURE_MSB;
  87   I2CMasterBuffer[2] = MPL115A2_ADDRESS | MPL115A2_READBIT;
  88   i2cEngine();
  89
  90   // Shift values to create properly formed integers
  91   *pressure = ((I2CSlaveBuffer[0] << 8) | (I2CSlaveBuffer[1])) >> 6;
  92   *temp = ((I2CSlaveBuffer[2] << 8) | (I2CSlaveBuffer[3])) >> 6;
  93
  94   return MPL115A2_ERROR_OK;
  95 }
  96
  97 /**************************************************************************/
  98 /*!
  99     @brief  Reads the factory-set coefficients
 100 */
 101 /**************************************************************************/
 102 mpl115a2Error_t mpl115a2ReadCoefficients(void)
 103 {
 104   int16_t a0coeff;
 105   int16_t b1coeff;
 106   int16_t b2coeff;
 107   int16_t c12coeff;
 108
 109   // Clear write buffers
 110   uint32_t i;
 111   for ( i = 0; i < I2C_BUFSIZE; i++ )
 112   {
 113     I2CMasterBuffer[i] = 0x00;
 114     I2CSlaveBuffer[i] = 0x00;
 115   }
 116
 117   I2CWriteLength = 2;
 118   I2CReadLength = 8;
 119   I2CMasterBuffer[0] = MPL115A2_ADDRESS;
 120   I2CMasterBuffer[1] = MPL115A2_REGISTER_A0_COEFF_MSB;
 121   I2CMasterBuffer[2] = MPL115A2_ADDRESS | MPL115A2_READBIT;
 122   i2cEngine();
 123
 124   a0coeff = (I2CSlaveBuffer[0] << 8 ) | I2CSlaveBuffer[1];
 125   b1coeff = (I2CSlaveBuffer[2] << 8 ) | I2CSlaveBuffer[3];
 126   b2coeff = (I2CSlaveBuffer[4] << 8 ) | I2CSlaveBuffer[5];
 127   c12coeff = ((I2CSlaveBuffer[6] << 8 ) | I2CSlaveBuffer[7]) >> 2;
 128
 129   _mpl115a2_a0 = (float)a0coeff / 8;
 130   _mpl115a2_b1 = (float)b1coeff / 8192;
 131   _mpl115a2_b2 = (float)b2coeff / 16384;
 132   _mpl115a2_c12 = (float)c12coeff / 4194304;
 133
 134   return MPL115A2_ERROR_OK;
 135 }
 136
 137 /**************************************************************************/
 138 /*!
 139     @brief  Initialises the I2C block
 140 */
 141 /**************************************************************************/
 142 mpl115a2Error_t mpl115a2Init(void)
 143 {
 144   mpl115a2Error_t error = MPL115A2_ERROR_OK;
 145
 146   // Initialise I2C
 147   if (i2cInit(I2CMASTER) == false)
 148   {
 149     return MPL115A2_ERROR_I2CINIT;    /* Fatal error */
 150   }
 151
 152   // Coefficients only need to be read once
 153   mpl115a2ReadCoefficients();
 154
 155   _mpl115a2Initialised = true;
 156   return error;
 157 }
 158
 159 /**************************************************************************/
 160 /*!
 161     @brief  Gets the compensated pressure level in kPa
 162 */
 163 /**************************************************************************/
 164 mpl115a2Error_t mpl115a2GetPressure(float *pressure)
 165 {
 166   uint16_t  Padc, Tadc;
 167   float     Pcomp;
 168
 169   mpl115a2Error_t error = MPL115A2_ERROR_OK;
 170
 171   // Make sure the coefficients have been read, etc.
 172   if (!_mpl115a2Initialised) mpl115a2Init();
 173
 174   // Get raw pressure and temperature settings
 175   error = mpl115a2ReadPressureTemp(&Padc, &Tadc);
 176   if (error) return error;
 177
 178   // See datasheet p.6 for evaluation sequence
 179   Pcomp = _mpl115a2_a0 + (_mpl115a2_b1 + _mpl115a2_c12 * Tadc ) * Padc + _mpl115a2_b2 * Tadc;
 180
 181   // Return pressure as floating point value
 182   *pressure = ((65.0F / 1023.0F)*(float)Pcomp) + 50;
 183
 184   return error;
 185 }