Limit i_set within range of MAX1968 chip

The REF pin of the MAX1968 on hardware revisions v2.x is missing a
buffer, loading the pin on every CPU ADC read. Avoid reading from it and
leave the pin floating on affected hardware revisions, and return the
nominal 1.5V instead.

src/channels.rs

@@ -18,13 +18,17 @@ use crate::{
     channel_state::ChannelState,
     command_parser::{CenterPoint, PwmPin},
     command_handler::JsonBuffer,
-    pins,
+    pins::{self, Channel0VRef, Channel1VRef},
     steinhart_hart,
     hw_rev,
 };
 
 pub const CHANNELS: usize = 2;
 pub const R_SENSE: f64 = 0.05;
+
+// as stated in the MAX1968 datasheet
+pub const MAX_TEC_I: f64 = 3.0;
+
 // DAC chip outputs 0-5v, which is then passed through a resistor dividor to provide 0-3v range
 const DAC_OUT_V_MAX: f64 = 3.0;
 
@@ -130,6 +134,11 @@ impl<'a> Channels<'a> {
     }
 
     pub fn set_i(&mut self, channel: usize, i_set: ElectricCurrent) -> ElectricCurrent {
+        // Silently clamp i_set
+        let i_ceiling = ElectricCurrent::new::<ampere>(MAX_TEC_I);
+        let i_floor = ElectricCurrent::new::<ampere>(-MAX_TEC_I);
+        let i_set = i_set.min(i_ceiling).max(i_floor);
+
         let vref_meas = match channel.into() {
             0 => self.channel0.vref_meas,
             1 => self.channel1.vref_meas,
@@ -203,20 +212,30 @@ impl<'a> Channels<'a> {
     pub fn read_vref(&mut self, channel: usize) -> ElectricPotential {
         match channel {
             0 => {
-                let sample = self.pins_adc.convert(
-                    &self.channel0.vref_pin,
-                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
-                );
-                let mv = self.pins_adc.sample_to_millivolts(sample);
-                ElectricPotential::new::<millivolt>(mv as f64)
+                match &self.channel0.vref_pin {
+                    Channel0VRef::Analog(vref_pin) => {
+                        let sample = self.pins_adc.convert(
+                            vref_pin,
+                            stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                        );
+                        let mv = self.pins_adc.sample_to_millivolts(sample);
+                        ElectricPotential::new::<millivolt>(mv as f64)
+                    },
+                    Channel0VRef::Disabled(_) => ElectricPotential::new::<volt>(1.5)
+                }
             }
             1 => {
-                let sample = self.pins_adc.convert(
-                    &self.channel1.vref_pin,
-                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
-                );
-                let mv = self.pins_adc.sample_to_millivolts(sample);
-                ElectricPotential::new::<millivolt>(mv as f64)
+                match &self.channel1.vref_pin {
+                    Channel1VRef::Analog(vref_pin) => {
+                        let sample = self.pins_adc.convert(
+                            vref_pin,
+                            stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                        );
+                        let mv = self.pins_adc.sample_to_millivolts(sample);
+                        ElectricPotential::new::<millivolt>(mv as f64)
+                    },
+                    Channel1VRef::Disabled(_) => ElectricPotential::new::<volt>(1.5)
+                }
             }
             _ => unreachable!(),
         }

src/fan_ctrl.rs

@@ -11,13 +11,11 @@ use uom::si::{
 use crate::{
     hw_rev::HWSettings,
     command_handler::JsonBuffer,
+    channels::MAX_TEC_I,
 };
 
 pub type FanPin = PwmChannels<TIM8, pwm::C4>;
 
-// as stated in the schematics
-const MAX_TEC_I: f32 = 3.0;
-
 const MAX_USER_FAN_PWM: f32 = 100.0;
 const MIN_USER_FAN_PWM: f32 = 1.0;
 
@@ -56,7 +54,7 @@ impl FanCtrl {
     pub fn cycle(&mut self, abs_max_tec_i: ElectricCurrent) {
         self.abs_max_tec_i = abs_max_tec_i.get::<ampere>() as f32;
         if self.fan_auto && self.hw_settings.fan_available {
-            let scaled_current = self.abs_max_tec_i / MAX_TEC_I;
+            let scaled_current = self.abs_max_tec_i / MAX_TEC_I as f32;
             // do not limit upper bound, as it will be limited in the set_pwm()
             let pwm = (MAX_USER_FAN_PWM * (scaled_current * (scaled_current * self.k_a + self.k_b) + self.k_c)) as u32;
             self.set_pwm(pwm);

src/pins.rs

@@ -66,21 +66,31 @@ pub trait ChannelPins {
     type TecUMeasPin;
 }
 
+pub enum Channel0VRef {
+    Analog(PA0<Analog>),
+    Disabled(PA0<Input<Floating>>),
+}
+
 impl ChannelPins for Channel0 {
     type DacSpi = Dac0Spi;
     type DacSync = PE4<Output<PushPull>>;
     type Shdn = PE10<Output<PushPull>>;
-    type VRefPin = PA0<Analog>;
+    type VRefPin = Channel0VRef;
     type ItecPin = PA6<Analog>;
     type DacFeedbackPin = PA4<Analog>;
     type TecUMeasPin = PC2<Analog>;
 }
 
+pub enum Channel1VRef {
+    Analog(PA3<Analog>),
+    Disabled(PA3<Input<Floating>>),
+}
+
 impl ChannelPins for Channel1 {
     type DacSpi = Dac1Spi;
     type DacSync = PF6<Output<PushPull>>;
     type Shdn = PE15<Output<PushPull>>;
-    type VRefPin = PA3<Analog>;
+    type VRefPin = Channel1VRef;
     type ItecPin = PB0<Analog>;
     type DacFeedbackPin = PA5<Analog>;
     type TecUMeasPin = PC3<Analog>;
@@ -150,13 +160,17 @@ impl Pins {
             gpioe.pe13, gpioe.pe14
         );
 
+        let hwrev = HWRev::detect_hw_rev(&HWRevPins {hwrev0: gpiod.pd0, hwrev1: gpiod.pd1,
+            hwrev2: gpiod.pd2, hwrev3: gpiod.pd3});
+        let hw_settings = hwrev.settings();
+
         let (dac0_spi, dac0_sync) = Self::setup_dac0(
             clocks, spi4,
             gpioe.pe2, gpioe.pe4, gpioe.pe6
         );
         let mut shdn0 = gpioe.pe10.into_push_pull_output();
         let _ = shdn0.set_low();
-        let vref0_pin = gpioa.pa0.into_analog();
+        let vref0_pin = if hwrev.major > 2 {Channel0VRef::Analog(gpioa.pa0.into_analog())} else {Channel0VRef::Disabled(gpioa.pa0)};
         let itec0_pin = gpioa.pa6.into_analog();
         let dac_feedback0_pin = gpioa.pa4.into_analog();
         let tec_u_meas0_pin = gpioc.pc2.into_analog();
@@ -176,7 +190,7 @@ impl Pins {
         );
         let mut shdn1 = gpioe.pe15.into_push_pull_output();
         let _ = shdn1.set_low();
-        let vref1_pin = gpioa.pa3.into_analog();
+        let vref1_pin = if hwrev.major > 2 {Channel1VRef::Analog(gpioa.pa3.into_analog())} else {Channel1VRef::Disabled(gpioa.pa3)};
         let itec1_pin = gpiob.pb0.into_analog();
         let dac_feedback1_pin = gpioa.pa5.into_analog();
         let tec_u_meas1_pin = gpioc.pc3.into_analog();
@@ -198,10 +212,6 @@ impl Pins {
             channel1,
         };
 
-        let hwrev = HWRev::detect_hw_rev(&HWRevPins {hwrev0: gpiod.pd0, hwrev1: gpiod.pd1,
-            hwrev2: gpiod.pd2, hwrev3: gpiod.pd3});
-        let hw_settings = hwrev.settings();
-
         let leds = Leds::new(gpiod.pd9, gpiod.pd10.into_push_pull_output(), gpiod.pd11.into_push_pull_output());
 
         let eeprom_scl = gpiob.pb8.into_alternate().set_open_drain();