BMP085_sam.cpp

00001 /*
00002    * mbed library to use a Bosch Sensortec BMP085 sensor
00003    * Copyright (c) 2010 Hiroshi Suga
00004    * Released under the MIT License: http://mbed.org/license/mit
00005    */
00006   
00007   /** @file BMP085.cpp
00008    * @brief mbed library to use a Bosch Sensortec BMP085 sensor
00009    * barometric pressure sensor BMP085 (Bosch Sensortec)
00010    * interface: I2C digital
00011    */
00012   
00013   #include "mbed.h"
00014   #include "BMP085.h"
00015   
00016   #define WEATHER_BMP085 0xee
00017   #define xpow(x, y) ((long)1 << y)
00018   
00019   /**
00020    * @brief Initializes interface (private I2C)
00021    * @param p_sda port of I2C SDA
00022    * @param p_scl port of I2C SCL
00023    * @param p_oss parameter of OSS
00024    */
00025   BMP085::BMP085 (PinName p_sda, PinName p_scl, BMP085_oss p_oss) : i2c(p_sda, p_scl) {
00026       init(p_oss);
00027   }
00028   
00029   /**
00030    * @brief Initializes interface (public I2C)
00031    * @param p_i2c instance of I2C class
00032    * @param p_oss parameter of OSS
00033    */
00034   BMP085::BMP085 (I2C& p_i2c, BMP085_oss p_oss) : i2c(p_i2c) { 
00035       init(p_oss);
00036   }
00037   
00038   /**
00039    * @brief Get temperature
00040    * @return temperature (`C)
00041    */
00042   float BMP085::get_temperature() {
00043       return temperature;
00044   }
00045   
00046   /**
00047    * @brief Get pressure
00048    * @return pressure (hPa)
00049    */
00050   float BMP085::get_pressure() {
00051       return pressure;
00052   }
00053   
00054   /**
00055    * @brief Update results
00056    */
00057   void BMP085::update () {
00058       long t, p, ut, up, x1, x2, x3, b3, b5, b6;
00059       unsigned long b4, b7;
00060   
00061       twi_writechar(WEATHER_BMP085, 0xf4, 0x2e);
00062       wait(0.01);
00063       ut = twi_readshort(WEATHER_BMP085, 0xf6);
00064   
00065       twi_writechar(WEATHER_BMP085, 0xf4, 0x34 | (oss << 6));
00066       wait(0.05);
00067       up = twi_readlong(WEATHER_BMP085, 0xf6) >> (8 - oss);
00068   
00069       x1 = ((ut - ac6) * ac5) / xpow(2, 15);
00070       x2 = ((long)mc * xpow(2, 11)) / (x1 + md);
00071       b5 = x1 + x2;
00072       t = (b5 + 8) / xpow(2, 4);
00073       temperature = (float)t / 10.0;
00074   
00075       b6 = b5 - 4000;
00076       x1 = (b2 * (b6 * b6 / xpow(2, 12))) / xpow(2, 11);
00077       x2 = (ac2 * b6) / xpow(2, 11);
00078       x3 = x1 + x2;
00079       b3 = ((((unsigned long)ac1 * 4 + x3) << oss) + 2) / 4;
00080       x1 = ac3 * b6 / xpow(2, 13);
00081       x2 = (b1 * (b6 * b6 / xpow(2, 12))) / xpow(2, 16);
00082       x3 = ((x1 + x2) + 2) / xpow(2, 2);
00083       b4 = (ac4 * (unsigned long)(x3 + 32768)) / xpow(2, 15);
00084       b7 = ((unsigned long)up - b3) * (50000 >> oss);
00085       if (b7 < (unsigned long)0x80000000) {
00086           p = (b7 * 2) / b4;
00087       } else {
00088           p = (b7 / b4) * 2;
00089       }
00090       x1 = (p / xpow(2, 8)) * (p / xpow(2, 8));
00091       x1 = (x1 * 3038) / xpow(2, 16);
00092       x2 = (-7357 * p) / xpow(2, 16);
00093       p = p + (x1 + x2 + 3791) / xpow(2, 4);
00094       pressure = (float)p / 100.0;
00095   }
00096   
00097   void BMP085::init (BMP085_oss p_oss) {
00098       ac1 = twi_readshort(WEATHER_BMP085, 0xaa);
00099       ac2 = twi_readshort(WEATHER_BMP085, 0xac);
00100       ac3 = twi_readshort(WEATHER_BMP085, 0xae);
00101       ac4 = twi_readshort(WEATHER_BMP085, 0xb0);
00102       ac5 = twi_readshort(WEATHER_BMP085, 0xb2);
00103       ac6 = twi_readshort(WEATHER_BMP085, 0xb4);
00104       b1 = twi_readshort(WEATHER_BMP085, 0xb6);
00105       b2 = twi_readshort(WEATHER_BMP085, 0xb8);
00106       mb = twi_readshort(WEATHER_BMP085, 0xba);
00107       mc = twi_readshort(WEATHER_BMP085, 0xbc);
00108       md = twi_readshort(WEATHER_BMP085, 0xbe);
00109       oss = p_oss;
00110   }
00111   
00112   unsigned short BMP085::twi_readshort (int id, int addr) {
00113       unsigned short i;
00114   
00115       i2c.start();
00116       i2c.write(id);
00117       i2c.write(addr);
00118   
00119       i2c.start();
00120       i2c.write(id | 1);
00121       i = i2c.read(1) << 8;
00122       i |= i2c.read(0);
00123       i2c.stop();
00124   
00125       return i;
00126   }
00127   
00128   unsigned long BMP085::twi_readlong (int id, int addr) {
00129       unsigned long i;
00130   
00131       i2c.start();
00132       i2c.write(id);
00133       i2c.write(addr);
00134   
00135       i2c.start();
00136       i2c.write(id | 1);
00137       i = i2c.read(1) << 16;
00138       i |= i2c.read(1) << 8;
00139       i |= i2c.read(0);
00140       i2c.stop();
00141   
00142       return i;
00143   }
00144   
00145   void BMP085::twi_writechar (int id, int addr, int dat) {
00146   
00147       i2c.start();
00148       i2c.write(id);
00149       i2c.write(addr);
00150       i2c.write(dat);
00151       i2c.stop();
00152   }