channel_state: recognize unplugged thermistor

src/ad7172/mod.rs

@@ -19,6 +19,8 @@ pub const SPI_MODE: spi::Mode = spi::Mode {
 /// 2 MHz
 pub const SPI_CLOCK: MegaHertz = MegaHertz(2);
 
+pub const MAX_VALUE: u32 = 0xFF_FFFF;
+
 
 #[derive(Clone, Copy, Debug)]
 #[repr(u8)]

src/channel_state.rs

@@ -63,7 +63,13 @@ impl ChannelState {
     }
 
     pub fn get_adc(&self) -> Option<ElectricPotential> {
-        Some(self.adc_calibration.convert_data(self.adc_data?))
+        let data = self.adc_data?;
+        if data == ad7172::MAX_VALUE {
+            // this means there is no thermistor plugged into the ADC.
+            None
+        } else {
+            Some(self.adc_calibration.convert_data(data))
+        }
     }
 
     /// Get `SENS[01]` input resistance

src/main.rs

@@ -182,10 +182,10 @@ fn main() -> ! {
 
                                             let state = channels.channel_state(channel);
                                             let _ = writeln!(
-                                                socket, "channel {}: t={:.0} adc{}={:.3} adc_r={:.3} vref={:.3} dac_feedback={:.3} itec={:.3} tec={:.3} tec_u_meas={:.3} r={:.3}",
+                                                socket, "channel {}: t={:.0} adc{}={:.3} adc_r={:?} vref={:.3} dac_feedback={:.3} itec={:.3} tec={:.3} tec_u_meas={:.3} r={:.3}",
                                                 channel, state.adc_time,
                                                 channel, adc_input.into_format_args(volt, Abbreviation),
-                                                state.get_sens().unwrap().into_format_args(ohm, Abbreviation),
+                                                state.get_sens().map(|sens| sens.into_format_args(ohm, Abbreviation)),
                                                 vref.into_format_args(volt, Abbreviation), dac_feedback.into_format_args(volt, Abbreviation),
                                                 itec.into_format_args(volt, Abbreviation), tec_i.into_format_args(ampere, Abbreviation),
                                                 tec_u_meas.into_format_args(volt, Abbreviation),