Remove stale reference to channel_state vref

Since VREF is an implementation detail, there shouldn't be a need to
include it in reports.

The ChannelState vref is removed along with it as its only use was to
save VREF measurements for later reporting.

src/channel_state.rs

@@ -26,8 +26,6 @@ pub struct ChannelState {
     pub adc_calibration: ad7172::ChannelCalibration,
     pub adc_time: Instant,
     pub adc_interval: Duration,
-    /// VREF for the TEC (1.5V)
-    pub vref: ElectricPotential,
     /// i_set 0A center point
     pub center: CenterPoint,
     pub dac_value: ElectricPotential,
@@ -44,8 +42,6 @@ impl ChannelState {
             adc_time: Instant::from_secs(0),
             // default: 10 Hz
             adc_interval: Duration::from_millis(100),
-            // updated later with Channels.read_vref()
-            vref: ElectricPotential::new::<volt>(1.5),
             center: CenterPoint::Vref,
             dac_value: ElectricPotential::new::<volt>(0.0),
             pid_engaged: false,

src/channels.rs

@@ -58,7 +58,6 @@ impl Channels {
         let pwm = pins.pwm;
         let mut channels = Channels { channel0, channel1, adc, pins_adc, pwm };
         for channel in 0..CHANNELS {
-            channels.channel_state(channel).vref = channels.read_vref(channel);
             channels.calibrate_dac_value(channel);
             channels.set_i(channel, ElectricCurrent::new::<ampere>(0.0));
         }
@@ -98,11 +97,8 @@ impl Channels {
     /// calculate the TEC i_set centerpoint
     pub fn get_center(&mut self, channel: usize) -> ElectricPotential {
         match self.channel_state(channel).center {
-            CenterPoint::Vref => {
-                let vref = self.read_vref(channel);
-                self.channel_state(channel).vref = vref;
-                vref
-            },
+            CenterPoint::Vref =>
+                self.read_vref(channel),
             CenterPoint::Override(center_point) =>
                 ElectricPotential::new::<volt>(center_point.into()),
         }
@@ -432,7 +428,6 @@ impl Channels {
     }
 
     fn report(&mut self, channel: usize) -> Report {
-        let vref = self.channel_state(channel).vref;
         let i_set = self.get_i(channel);
         let i_tec = self.read_itec(channel);
         let tec_i = self.get_tec_i(channel);
@@ -449,7 +444,6 @@ impl Channels {
                 .map(|temperature| temperature.get::<degree_celsius>()),
             pid_engaged: state.pid_engaged,
             i_set,
-            vref,
             dac_value,
             dac_feedback: self.read_dac_feedback(channel),
             i_tec,
@@ -547,7 +541,6 @@ pub struct Report {
     temperature: Option<f64>,
     pid_engaged: bool,
     i_set: ElectricCurrent,
-    vref: ElectricPotential,
     dac_value: ElectricPotential,
     dac_feedback: ElectricPotential,
     i_tec: ElectricPotential,