Diff: Barometer.cpp

Revision:

16:3e2468d4f4c1

Parent:

4:e759b8c756da

Child:

19:9e9753b87cfe

--- a/Barometer.cpp	Wed Mar 18 15:34:51 2015 +0000
+++ b/Barometer.cpp	Fri Mar 20 10:30:01 2015 +0000
@@ -1,117 +1,105 @@
 #include "Barometer.h"
 #define DEBUG "BMP280"
 #include "Logger.h"
+#include <cmath>
 
-Barometer::Barometer(I2C &i2c) : I2CPeripheral(i2c, 0xEC /* address */)
+Barometer::Barometer(I2C &i2c) : I2CPeripheral(i2c, 0xEC /* address */), startingAltitude(0)
 {
-    write_reg(0xE0, 0xB6); // reset
-    wait_ms(2); // cf. datasheet page 8, t_startup
-    const uint8_t chip_id = read_reg(0xD0);
-    if (chip_id == 0x58) {
+    if (powerOn()) {
+        INFO("Bosch Sensortec BMP280 atmospheric pressure sensor found");
         bmp280_read_calibration();
-        //setFilterCoefficient(kFilter_16x);
-        INFO("Bosch Sensortec BMP280 ready");
+        powerOff();
     } else {
-        WARN("Bosch Sensortec BMP280 not found (chip ID=0x%02x, expected=0x58)", chip_id);
+        WARN("Bosch Sensortec BMP280 atmospheric pressure sensor not found");
     }
 }
 
-// Calibration parameters stored on chip
-static uint16_t dig_T1;
-static int16_t dig_T2;
-static int16_t dig_T3;
-static uint16_t dig_P1;
-static int16_t dig_P2;
-static int16_t dig_P3;
-static int16_t dig_P4;
-static int16_t dig_P5;
-static int16_t dig_P6;
-static int16_t dig_P7;
-static int16_t dig_P8;
-static int16_t dig_P9;
+bool Barometer::powerOn() {
+    write_reg(0xE0, 0xB6); // reset
+    wait_ms(2); // cf. datasheet page 8, t_startup
+    return read_reg(0xD0) == 0x58; // verify chip ID
+}
+
+void Barometer::powerOff() {
+    // nothing to do
+}
+
+void Barometer::start() {
+    startingAltitude = 0;
+    lastPressure = 102000;
+    // set parameters for Bosch-recommended "Indoor navigation" preset
+    write_reg(0xF5, 0x10); // 0.5ms t_standby, IIR coefficient=16
+    write_reg(0xF4, 0x57); // 2x oversampling for temperature, 16x for pressure and power mode "normal"
+}
+
+void Barometer::stop() {
+    write_reg(0xF4, 0x54); // keep the oversampling settings but set power mode to "sleep"
+}
 
-void Barometer::bmp280_read_cal_reg(const uint8_t reg, char* val)
-{
-    *val = read_reg(reg);
-    *(val + 1) = read_reg(reg + 1);
+Vector3 Barometer::read() {
+    uint8_t buffer[6];
+    for (int i = 0; i < 6; i++)
+        buffer[i] =  read_reg(0xF7 + i);
+
+    const uint32_t adc_P = ((buffer[0] << 16) | (buffer[1] << 8) | buffer[2]) >> 4;
+    const uint32_t adc_T = ((buffer[3] << 16) | (buffer[4] << 8) | buffer[5]) >> 4;
+    
+    const float celsius = bmp280_val_to_temp(adc_T) - 20; // 20 degree offset (?)
+    const float A = 0.5;
+    const float pa = A * bmp280_val_to_pa(adc_P) + (1-A)*lastPressure;
+    lastPressure = pa;
+    
+    const float centimeter = (pressureToAltitude(pa) * 100.0) - startingAltitude;
+    if (startingAltitude == 0)
+        startingAltitude = centimeter;
+    
+    return Vector3(celsius, pa, centimeter);
+}
+
+float Barometer::pressureToAltitude(const float pa) const {    
+    return -44330.7692 * (pow(pa * 0.0000098692, 0.1902632365) - 1);
 }
 
 void Barometer::bmp280_read_calibration()
 {
-    bmp280_read_cal_reg(0x88, (char*)&dig_T1);
-    bmp280_read_cal_reg(0x8A, (char*)&dig_T2);
-    bmp280_read_cal_reg(0x8C, (char*)&dig_T3);
-    bmp280_read_cal_reg(0x8E, (char*)&dig_P1);
-    bmp280_read_cal_reg(0x90, (char*)&dig_P2);
-    bmp280_read_cal_reg(0x92, (char*)&dig_P3);
-    bmp280_read_cal_reg(0x94, (char*)&dig_P4);
-    bmp280_read_cal_reg(0x96, (char*)&dig_P5);
-    bmp280_read_cal_reg(0x98, (char*)&dig_P6);
-    bmp280_read_cal_reg(0x9A, (char*)&dig_P7);
-    bmp280_read_cal_reg(0x9C, (char*)&dig_P8);
-    bmp280_read_cal_reg(0x9E, (char*)&dig_P9);
+    struct {
+        uint16_t dig_T1;
+        int16_t  dig_T2;
+        int16_t  dig_T3;
+        uint16_t dig_P1;
+        int16_t  dig_P2;
+        int16_t  dig_P3;
+        int16_t  dig_P4;
+        int16_t  dig_P5;
+        int16_t  dig_P6;
+        int16_t  dig_P7;
+        int16_t  dig_P8;
+        int16_t  dig_P9;
+    } cal_data;
+    
+    read_reg(0x88, (uint8_t*)&cal_data, sizeof cal_data);
+    
+    dig_T1 = cal_data.dig_T1;
+    dig_T2 = cal_data.dig_T2;
+    dig_T3 = cal_data.dig_T3;
+    dig_P1 = cal_data.dig_P1;
+    dig_P2 = cal_data.dig_P2;
+    dig_P3 = cal_data.dig_P3;
+    dig_P4 = cal_data.dig_P4;
+    dig_P5 = cal_data.dig_P5;
+    dig_P6 = cal_data.dig_P6;
+    dig_P7 = cal_data.dig_P7;
+    dig_P8 = cal_data.dig_P8;
+    dig_P9 = cal_data.dig_P9;
+
     LOG("Calibration parameters: T=[%u, %d, %d] P=[%u, %d, %d, %d, %d, %d, %d, %d, %d]",
         dig_T1, dig_T2, dig_T3,
         dig_P1, dig_P2, dig_P3, dig_P4, dig_P5, dig_P6, dig_P7, dig_P8, dig_P9);
 }
 
-enum Oversampling {
-    kSkip = 0,
-    kOversample_1x = 1,
-    kOversample_2x = 2,
-    kOversample_4x = 3,
-    kOversample_8x = 4,
-    kOversample_16x = 5,
-};
-
-// Time taken to read the pressure at a particular oversampling
-// cf. page 18
-static float waitTime_ms[] = {
-    0, // skip
-    6.4, // 1x
-    8.7, // 2x
-    13.3, // 4x
-    22.5, // 8x
-    50, // 16x
-};
-
-enum Filtering {
-    kFilter_None = 0,
-    kFilter_2x = 1,
-    kFilter_4x = 2,
-    kFilter_8x = 3,
-    kFilter_16x = 4
-};
-
-void Barometer::setFilterCoefficient(const uint8_t iir)
-{
-    write_reg(0xF5, (iir & 0x07) << 1);
-    INFO("Filter coefficient => %dx", 1 << iir);
-}
-
-void Barometer::takeMeasurement(const uint8_t tmpovr,
-                                const uint8_t psrovr)
-{
-    // Start a forced measurement
-    write_reg(0xF4,
-              ((tmpovr & 0x07) << 5) |
-              ((psrovr & 0x07) << 2) |
-              0x01 /* force reading mode */);
-
-    // wait until it's done
-    //wait_ms(waitTime_ms[psrovr]); // XXX: what does this mean for BLE?
-}
-
-// These typedefs are for Bosch's conversion algorithms below
-typedef uint32_t BMP280_U32_t;
-typedef int32_t BMP280_S32_t;
-typedef int64_t BMP280_S64_t;
-
 // Returns temperature in DegC, resolution is 0.01 DegC. Output value of “5123” equals 51.23 DegC.
-// t_fine carries fine temperature as global value
-static BMP280_S32_t t_fine;
-
-double bmp280_val_to_temp(BMP280_S32_t adc_T)
+// XXX: converted to return float result directly
+float Barometer::bmp280_val_to_temp(BMP280_S32_t adc_T)
 {
     BMP280_S32_t var1, var2, T;
     var1 = ((((adc_T>>3) - ((BMP280_S32_t)dig_T1<<1))) * ((BMP280_S32_t)dig_T2)) >> 11;
@@ -119,12 +107,14 @@
             ((BMP280_S32_t)dig_T3)) >> 14;
     t_fine = var1 + var2;
     T =(t_fine*5+128)>>8;
-    return T / 100.0;
+    return T / 100.0f;
 }
 
 // Returns pressure in Pa as unsigned 32 bit integer in Q24.8 format (24 integer bits and 8 fractional bits).
 // Output value of “24674867” represents 24674867/256 = 96386.2 Pa = 963.862 hPa
-double bmp280_val_to_pa(BMP280_S32_t adc_P)
+// XXX: converted it to return a float directly.
+// XXX: uses t_fine, so call temperature conversion BEFORE calling this.
+float Barometer::bmp280_val_to_pa(BMP280_S32_t adc_P)
 {
     BMP280_S64_t var1, var2, p;
     var1 = ((BMP280_S64_t)t_fine) - 128000;
@@ -141,36 +131,5 @@
     var1 = (((BMP280_S64_t)dig_P9) * (p>>13) * (p>>13)) >> 25;
     var2 = (((BMP280_S64_t)dig_P8) * p) >> 19;
     p = ((p + var1 + var2) >> 8) + (((BMP280_S64_t)dig_P7)<<4);
-    return ((BMP280_U32_t)p) / 256.0;
-}
-
-double Barometer::getPressure()
-{
-    takeMeasurement(kSkip, kOversample_16x);
-    const uint8_t msb = read_reg(0xF7);
-    const uint8_t lsb = read_reg(0xF8);
-    const uint8_t xlsb = read_reg(0xF9);
-    const uint32_t val = (msb << 12) | (lsb << 4) | ((xlsb & 0xF0) >> 4);
-    return bmp280_val_to_pa(val) / 100.0;
+    return ((BMP280_U32_t)p) / 256.0f;
 }
-
-double Barometer::getTemperature()
-{
-    takeMeasurement(kOversample_1x, kSkip);
-    const uint8_t msb = read_reg(0xFA);
-    const uint8_t lsb = read_reg(0xFB);
-    const uint8_t xlsb = read_reg(0xFC);
-    const uint32_t val = (msb << 12) | (lsb << 4) | ((xlsb & 0xF0) >> 4);
-    return bmp280_val_to_temp(val);
-}
-
-double Barometer::getAltitude()
-{
-    const double R = 287.05; // general gas constant
-    const double g = 9.80665; // acceleration due to gravity
-    const double T = 297.6; // supposed to be average temperature between p and p0
-    const double p0 = 1000.0; // hPa sea level
-    const double p = getPressure();
-    const double h = (R / g) * T * log(p0 / p);
-    return h;
-}
\ No newline at end of file