README: Document swap status in report

Signed-off-by: Egor Savkin <es@m-labs.hk>

README.md

@@ -256,21 +256,22 @@ Use the bare `report` command to obtain a single report. Enable
 continuous reporting with `report mode on`. Reports are JSON objects
 with the following keys.
 
-| Key            | Unit            | Description                                          |
+| Key               | Unit            | Description                                                        |
-| ---            | :---:           | ---                                                  |
+| ---               | :---:           | ---                                                                |
-| `channel`      | Integer         | Channel `0`, or `1`                                  |
+| `channel`         | Integer         | Channel `0`, or `1`                                                |
-| `time`         | Seconds         | Temperature measurement time                         |
+| `time`            | Seconds         | Temperature measurement time                                       |
-| `adc`          | Volts           | AD7172 input                                         |
+| `adc`             | Volts           | AD7172 input                                                       |
-| `sens`         | Ohms            | Thermistor resistance derived from `adc`             |
+| `sens`            | Ohms            | Thermistor resistance derived from `adc`                           |
-| `temperature`  | Degrees Celsius | Steinhart-Hart conversion result derived from `sens` |
+| `temperature`     | Degrees Celsius | Steinhart-Hart conversion result derived from `sens`               |
-| `pid_engaged`  | Boolean         | `true` if in closed-loop mode                        |
+| `pid_engaged`     | Boolean         | `true` if in closed-loop mode                                      |
-| `i_set`        | Amperes         | TEC output current                                   |
+| `current_swapped` | Boolean         | `true` if TEC current direction is swapped relative to front panel |
-| `dac_value`    | Volts           | AD5680 output derived from `i_set`                   |
+| `i_set`           | Amperes         | TEC output current                                                 |
-| `dac_feedback` | Volts           | ADC measurement of the AD5680 output                 |
+| `dac_value`       | Volts           | AD5680 output derived from `i_set`                                 |
-| `i_tec`        | Volts           | MAX1968 TEC current monitor                          |
+| `dac_feedback`    | Volts           | ADC measurement of the AD5680 output                               |
-| `tec_i`        | Amperes         | TEC output current feedback derived from `i_tec`     |
+| `i_tec`           | Volts           | MAX1968 TEC current monitor                                        |
-| `tec_u_meas`   | Volts           | Measurement of the voltage across the TEC            |
+| `tec_i`           | Amperes         | TEC output current feedback derived from `i_tec`                   |
-| `pid_output`   | Amperes         | PID control output                                   |
+| `tec_u_meas`      | Volts           | Measurement of the voltage across the TEC                          |
+| `pid_output`      | Amperes         | PID control output                                                 |
 
 Note: With Thermostat v2 and below, the voltage and current readouts `i_tec` and `tec_i` are noisy without the hardware fix shown in [this PR][https://git.m-labs.hk/M-Labs/thermostat/pulls/105].
 

src/channels.rs

@@ -157,11 +157,13 @@ impl Channels {
     }
 
     pub fn set_i(&mut self, channel: usize, i_set: ElectricCurrent) -> ElectricCurrent {
-        let mut i_set = i_set.min(MAX_TEC_I).max(-MAX_TEC_I);
+        let i_set = i_set.min(MAX_TEC_I).max(-MAX_TEC_I);
         self.channel_state(channel).i_set = i_set;
-        if self.channel_state(channel).polarity_swapped {
+        let negate = if self.channel_state(channel).polarity_swapped {
-            i_set = -i_set;
+            -1.0
-        }
+        } else {
+            1.0
+        };
         let vref_meas = match channel.into() {
             0 => self.channel0.vref_meas,
             1 => self.channel1.vref_meas,
@@ -169,9 +171,9 @@ impl Channels {
         };
         let center_point = vref_meas;
         let r_sense = ElectricalResistance::new::<ohm>(R_SENSE);
-        let voltage = i_set * 10.0 * r_sense + center_point;
+        let voltage = negate * i_set * 10.0 * r_sense + center_point;
         let voltage = self.set_dac(channel, voltage);
-        let i_set = (voltage - center_point) / (10.0 * r_sense);
+        let i_set = negate * (voltage - center_point) / (10.0 * r_sense);
         i_set
     }
 
@@ -477,6 +479,19 @@ impl Channels {
         (duty * MAX_TEC_I_DUTY_TO_CURRENT_RATE, max)
     }
 
+    pub fn swap_polarity(&mut self, channel: usize, swapped: bool) {
+        if self.channel_state(channel).polarity_swapped != swapped {
+            let i_set = self.channel_state(channel).i_set;
+            let max_i_pos = self.get_max_i_pos(channel).0;
+            let max_i_neg = self.get_max_i_neg(channel).0;
+
+            self.channel_state(channel).polarity_swapped = swapped;
+            self.set_i(channel, i_set);
+            self.set_max_i_pos(channel, max_i_pos);
+            self.set_max_i_neg(channel, max_i_neg);
+        }
+    }
+
     fn report(&mut self, channel: usize) -> Report {
         let i_set = self.get_i(channel);
         let i_tec = self.adc_read(channel, PinsAdcReadTarget::ITec, 16);

src/command_handler.rs

@@ -182,10 +182,7 @@ impl Handler {
     }
 
     fn swap_polarity (socket: &mut TcpSocket, channels: &mut Channels, channel: usize, swapped: bool) -> Result<Handler, Error> {
-        channels.channel_state(channel).polarity_swapped = swapped;
+        channels.swap_polarity(channel, swapped);
-        let channel_state = channels.channel_state(channel);
-        let i_set = channel_state.i_set;
-        channels.set_i(channel, i_set);
         send_line(socket, b"{}");
         Ok(Handler::Handled)
     }

src/config.rs

@@ -20,6 +20,7 @@ pub struct ChannelConfig {
     pid_target: f32,
     pid_engaged: bool,
     i_set: ElectricCurrent,
+    polarity_swapped: bool,
     sh: steinhart_hart::Parameters,
     pwm: PwmLimits,
     /// uses variant `PostFilter::Invalid` instead of `None` to save space
@@ -45,7 +46,8 @@ impl ChannelConfig {
             pid: state.pid.parameters.clone(),
             pid_target: state.pid.target as f32,
             pid_engaged: state.pid_engaged,
-            i_set: i_set,
+            i_set,
+            polarity_swapped: state.polarity_swapped,
             sh: state.sh.clone(),
             pwm,
             adc_postfilter,
@@ -68,6 +70,7 @@ impl ChannelConfig {
         };
         let _ = channels.adc.set_postfilter(channel as u8, adc_postfilter);
         let _ = channels.set_i(channel, self.i_set);
+        channels.swap_polarity(channel, self.polarity_swapped);
     }
 }