Thermostat: Add fn to calibrate ADC's VDDA

- ADC1 exclusive feature
- Calibrated VDDA val can be passed to other ADCs to adjust gain error

src/thermostat/max1968.rs

@@ -115,11 +115,17 @@ impl<C: ChannelPins> MAX1968Phy<C> {
 
 impl MAX1968 {
     pub fn new(phy_ch0: MAX1968Phy<Channel0>, adc1: ADC1) -> Self {
+        // Set ADC to a slowest sampling interval for more accurate calibration
         let config = AdcConfig::default()
-            .clock(config::Clock::Pclk2_div_2)
+            .clock(config::Clock::Pclk2_div_8)
             .default_sample_time(config::SampleTime::Cycles_480);
+        let mut pins_adc = Adc::adc1(adc1, true, config);
+        pins_adc.calibrate();
 
-        let pins_adc = Adc::adc1(adc1, true, config);
+        let config = AdcConfig::default()
+            .clock(config::Clock::Pclk2_div_8)
+            .default_sample_time(config::SampleTime::Cycles_480);
+        pins_adc.apply_config(config);
 
         MAX1968 {
             phy: phy_ch0,
@@ -127,6 +133,12 @@ impl MAX1968 {
         }
     }
 
+    // Return the calibrated VDDA Voltage
+    // Can be used to set reference voltage for other ADC
+    pub fn get_calibrated_vdda(&mut self) -> u32 {
+        self.pins_adc.reference_voltage()
+    }
+
     pub fn power_down(&mut self) {
         self.phy.shdn.set_low();
     }

src/thermostat/thermostat.rs

@@ -301,6 +301,11 @@ impl Thermostat{
             max_i_neg: TecSettingsSummaryField { value: self.tec_setting.max_i_neg_set, max: TecSettings::MAX_I_NEG_CURRENT },
         }
     }
+
+    pub fn get_calibrated_vdda(&mut self) -> u32 {
+        self.max1968.get_calibrated_vdda()
+    }
+
 }
 
 #[derive(Miniconf)]