#11 Add optional temperature offset

src/calc.rs

@@ -41,13 +41,23 @@ impl Calc {
         durval
     }
 
-    pub fn calc_temperature(calib: &CalibData, temp_adc: u32) -> (i16, i32) {
+    ///
+    /// * `calib` - Calibration data used during initalization
+    /// * `temp_adc`
+    /// * `temp_offset` - If set, the temperature t_fine will be increased by given
+    ///                   value in celsius. Temperature offset in Celsius, e.g. 4, -8, 1.25
+    pub fn calc_temperature(calib: &CalibData, temp_adc: u32, temp_offset: Option<i32>) -> (i16, i32) {
         let var1: i64 = (temp_adc as (i64) >> 3) - ((calib.par_t1 as (i64)) << 1);
         let var2: i64 = (var1 * (calib.par_t2 as i64)) >> 11;
         let var3: i64 = ((var1 >> 1) * (var1 >> 1)) >> 12;
         let var3: i64 = (var3 * ((calib.par_t3 as i64) << 4)) >> 14;
         // TODO really assign here ?
-        let t_fine: i32 = (var2 + var3) as (i32);
+        let mut temp_offset = temp_offset.unwrap_or(0);
+        if temp_offset < 0 {
+            temp_offset = -1 * ((((temp_offset.abs() * 100) << 8) - 128) / 5);
+        }
+
+        let t_fine: i32 = (var2 + var3) as i32  + temp_offset;
         let calc_temp: i16 = (((t_fine * 5) + 128) >> 8) as i16;
         (calc_temp, t_fine)
     }

src/lib.rs

@@ -591,6 +591,7 @@ where
 
         // Restore previous intended power mode
         self.power_mode = intended_power_mode;
+        self.tph_sett = tph_sett;
         Ok(())
     }
 
@@ -931,7 +932,7 @@ where
             data.status = data.status | buff[14] & BME680_HEAT_STAB_MSK;
 
             if data.status & BME680_NEW_DATA_MSK != 0 {
-                let (temp, t_fine) = Calc::calc_temperature(&self.calib, adc_temp);
+                let (temp, t_fine) = Calc::calc_temperature(&self.calib, adc_temp, self.tph_sett.temperature_offset);
                 debug!(
                     "adc_temp: {} adc_pres: {} adc_hum: {} adc_gas_res: {}, t_fine: {}",
                     adc_temp, adc_pres, adc_hum, adc_gas_res, t_fine

src/settings.rs

@@ -70,6 +70,8 @@ pub struct TphSett {
     pub os_pres: Option<OversamplingSetting>,
     /// Filter coefficient
     pub filter: Option<IIRFilterSize>,
+    /// If set, the temperature t_fine will be increased by the given value in celsius.
+    pub temperature_offset: Option<i32>,
 }
 
 impl Clone for TphSett {
@@ -228,6 +230,12 @@ impl SettingsBuilder {
         self
     }
 
+    /// Temperature offset in Celsius, e.g. 4, -8, 1.25
+    pub fn with_temperature_offset(mut self, offset: i32) -> SettingsBuilder {
+        self.sensor_settings.tph_sett.temperature_offset = Some(offset);
+        self
+    }
+
     pub fn build(self) -> Settings {
         (self.sensor_settings, self.desired_settings)
     }