Merge #1024

1024: stm32/adc: Remove voltage and temperature conversions r=Dirbaio a=GrantM11235

The current conversion utilities are confusing and a bit of a footgun. (Two out of the three examples got it wrong! They didn't measure vref at all, so all the conversions are completely wrong if vcca isn't 3.3v)

I think we should eventually have some sort of conversion utilities in the HAL, but for now I think it is best to just remove it and let the users do their own math.

cc `@chemicstry` 

Co-authored-by: Grant Miller <GrantM11235@gmail.com>

examples/stm32f1/src/bin/adc.rs

@@ -16,11 +16,19 @@ async fn main(_spawner: Spawner) {
     let mut adc = Adc::new(p.ADC1, &mut Delay);
     let mut pin = p.PB1;
 
-    let mut vref = adc.enable_vref(&mut Delay);
-    adc.calibrate(&mut vref);
+    let mut vrefint = adc.enable_vref(&mut Delay);
+    let vrefint_sample = adc.read(&mut vrefint);
+    let convert_to_millivolts = |sample| {
+        // From http://www.st.com/resource/en/datasheet/CD00161566.pdf
+        // 5.3.4 Embedded reference voltage
+        const VREFINT_MV: u32 = 1200; // mV
+
+        (u32::from(sample) * VREFINT_MV / u32::from(vrefint_sample)) as u16
+    };
+
     loop {
         let v = adc.read(&mut pin);
-        info!("--> {} - {} mV", v, adc.to_millivolts(v));
+        info!("--> {} - {} mV", v, convert_to_millivolts(v));
         Timer::after(Duration::from_millis(100)).await;
     }
 }

examples/stm32f4/src/bin/adc.rs

@@ -24,19 +24,44 @@ async fn main(_spawner: Spawner) {
     // Startup delay can be combined to the maximum of either
     delay.delay_us(Temperature::start_time_us().max(VrefInt::start_time_us()));
 
+    let vrefint_sample = adc.read_internal(&mut vrefint);
+
+    let convert_to_millivolts = |sample| {
+        // From http://www.st.com/resource/en/datasheet/DM00071990.pdf
+        // 6.3.24 Reference voltage
+        const VREFINT_MV: u32 = 1210; // mV
+
+        (u32::from(sample) * VREFINT_MV / u32::from(vrefint_sample)) as u16
+    };
+
+    let convert_to_celcius = |sample| {
+        // From http://www.st.com/resource/en/datasheet/DM00071990.pdf
+        // 6.3.22 Temperature sensor characteristics
+        const V25: i32 = 760; // mV
+        const AVG_SLOPE: f32 = 2.5; // mV/C
+
+        let sample_mv = convert_to_millivolts(sample) as i32;
+
+        (sample_mv - V25) as f32 / AVG_SLOPE + 25.0
+    };
+
+    info!("VrefInt: {}", vrefint_sample);
+    const MAX_ADC_SAMPLE: u16 = (1 << 12) - 1;
+    info!("VCCA: {} mV", convert_to_millivolts(MAX_ADC_SAMPLE));
+
     loop {
         // Read pin
         let v = adc.read(&mut pin);
-        info!("PC1: {} ({} mV)", v, adc.to_millivolts(v));
+        info!("PC1: {} ({} mV)", v, convert_to_millivolts(v));
 
         // Read internal temperature
         let v = adc.read_internal(&mut temp);
-        let celcius = Temperature::to_celcius(adc.to_millivolts(v));
+        let celcius = convert_to_celcius(v);
         info!("Internal temp: {} ({} C)", v, celcius);
 
         // Read internal voltage reference
         let v = adc.read_internal(&mut vrefint);
-        info!("VrefInt: {} ({} mV)", v, adc.to_millivolts(v));
+        info!("VrefInt: {}", v);
 
         Timer::after(Duration::from_millis(100)).await;
     }

examples/stm32f7/src/bin/adc.rs

@@ -16,9 +16,19 @@ async fn main(_spawner: Spawner) {
     let mut adc = Adc::new(p.ADC1, &mut Delay);
     let mut pin = p.PA3;
 
+    let mut vrefint = adc.enable_vrefint();
+    let vrefint_sample = adc.read_internal(&mut vrefint);
+    let convert_to_millivolts = |sample| {
+        // From http://www.st.com/resource/en/datasheet/DM00273119.pdf
+        // 6.3.27 Reference voltage
+        const VREFINT_MV: u32 = 1210; // mV
+
+        (u32::from(sample) * VREFINT_MV / u32::from(vrefint_sample)) as u16
+    };
+
     loop {
         let v = adc.read(&mut pin);
-        info!("--> {} - {} mV", v, adc.to_millivolts(v));
+        info!("--> {} - {} mV", v, convert_to_millivolts(v));
         Timer::after(Duration::from_millis(100)).await;
     }
 }