thermostat: Save the user config-ed value directly

- the firmware recorded the actual value set with quantization errors or
    other errors
- this caused confusion for the user when they read back the settings

src/thermostat/thermostat.rs

@@ -213,13 +213,14 @@ impl Thermostat {
     }
 
     pub fn power_up(&mut self) {
-        self.max1968.power_up();
+        if !self.max1968.is_powered_on() {
+            self.max1968.power_up();
+            self.pid_ctrl_ch0.reset_pid_state();
+        }
     }
 
     pub fn power_down(&mut self) {
         self.max1968.power_down();
-        self.pid_ctrl_ch0.reset_pid_state();
-        self.set_i(ElectricCurrent::new::<ampere>(0.0));
     }
 
     fn set_center_pt(&mut self, value: ElectricPotential) {
@@ -232,36 +233,39 @@ impl Thermostat {
 
     pub fn set_i(&mut self, i_tec: ElectricCurrent) -> ElectricCurrent {
         let voltage = i_tec * 10.0 * R_SENSE + self.tec_settings.center_pt;
-        let voltage = self.max1968.set_dac(voltage, self.max1968.dac_out_range);
+        let _voltage = self.max1968.set_dac(voltage, self.max1968.dac_out_range);
 
-        self.tec_settings.i_set = (voltage - self.tec_settings.center_pt) / (10.0 * R_SENSE);
+        self.tec_settings.i_set = i_tec;
         self.tec_settings.i_set
     }
 
     pub fn set_max_v(&mut self, max_v: ElectricPotential) -> ElectricPotential {
         let duty = (max_v / TecSettings::MAX_V_DUTY_TO_VOLTAGE_RATE).get::<ratio>();
-        let duty = self
+        let _duty = self
             .max1968
             .set_pwm(PwmPinsEnum::MaxV, duty as f64, TecSettings::MAX_V_DUTY_MAX);
-        self.tec_settings.max_v_set = duty as f32 * TecSettings::MAX_V_DUTY_TO_VOLTAGE_RATE;
+
+        self.tec_settings.max_v_set = max_v;
         self.tec_settings.max_v_set
     }
 
     pub fn set_max_i_pos(&mut self, max_i_pos: ElectricCurrent) -> ElectricCurrent {
         let duty = (max_i_pos / TecSettings::MAX_I_POS_NEG_DUTY_TO_CURRENT_RATE).get::<ratio>();
-        let duty = self
+        let _duty = self
             .max1968
             .set_pwm(PwmPinsEnum::MaxPosI, duty as f64, TecSettings::MAX_I_POS_DUTY_MAX);
-        self.tec_settings.max_i_pos_set = duty as f32 * TecSettings::MAX_I_POS_NEG_DUTY_TO_CURRENT_RATE;
+
+        self.tec_settings.max_i_pos_set = max_i_pos;
         self.tec_settings.max_i_pos_set
     }
 
     pub fn set_max_i_neg(&mut self, max_i_neg: ElectricCurrent) -> ElectricCurrent {
         let duty = (max_i_neg / TecSettings::MAX_I_POS_NEG_DUTY_TO_CURRENT_RATE).get::<ratio>();
-        let duty = self
+        let _duty = self
             .max1968
             .set_pwm(PwmPinsEnum::MaxNegI, duty as f64, TecSettings::MAX_I_NEG_DUTY_MAX);
-        self.tec_settings.max_i_neg_set = duty as f32 * TecSettings::MAX_I_POS_NEG_DUTY_TO_CURRENT_RATE;
+
+        self.tec_settings.max_i_neg_set = max_i_neg;
         self.tec_settings.max_i_neg_set
     }