Stop i_set from fluctuating in every report

i_set is a user-provided value that shouldn't fluctuate with every VREF
measurement. Storing i_set as channel state is the simplest way to avoid
that.

src/channel_state.rs

@@ -2,11 +2,13 @@ use smoltcp::time::{Duration, Instant};
 use uom::si::{
     f64::{
         ElectricPotential,
+        ElectricCurrent,
         ElectricalResistance,
         ThermodynamicTemperature,
         Time,
     },
     electric_potential::volt,
+    electric_current::ampere,
     electrical_resistance::ohm,
     thermodynamic_temperature::degree_celsius,
     time::millisecond,
@@ -29,6 +31,7 @@ pub struct ChannelState {
     /// i_set 0A center point
     pub center: CenterPoint,
     pub dac_value: ElectricPotential,
+    pub i_set: ElectricCurrent,
     pub pid_engaged: bool,
     pub pid: pid::Controller,
     pub sh: sh::Parameters,
@@ -44,6 +47,7 @@ impl ChannelState {
             adc_interval: Duration::from_millis(100),
             center: CenterPoint::Vref,
             dac_value: ElectricPotential::new::<volt>(0.0),
+            i_set: ElectricCurrent::new::<ampere>(0.0),
             pid_engaged: false,
             pid: pid::Controller::new(pid::Parameters::default()),
             sh: sh::Parameters::default(),

src/channels.rs

@@ -113,11 +113,8 @@ impl<'a> Channels<'a> {
     }
 
     pub fn get_i(&mut self, channel: usize) -> ElectricCurrent {
-        let center_point = self.get_center(channel);
-        let r_sense = ElectricalResistance::new::<ohm>(R_SENSE);
-        let voltage = self.get_dac(channel);
-        let i_tec = (voltage - center_point) / (10.0 * r_sense);
-        i_tec
+        let i_set = self.channel_state(channel).i_set;
+        i_set
     }
 
     /// i_set DAC
@@ -143,6 +140,7 @@ impl<'a> Channels<'a> {
         let voltage = i_tec * 10.0 * r_sense + center_point;
         let voltage = self.set_dac(channel, voltage);
         let i_tec = (voltage - center_point) / (10.0 * r_sense);
+        self.channel_state(channel).i_set = i_tec;
         i_tec
     }