Merge pull request #63 from stm32-rs/feature/absolute-adc

ADC absolute voltage measurement

Author: andresv

examples/adc.rs

@@ -9,7 +9,7 @@ extern crate panic_halt;
 extern crate stm32g0xx_hal as hal;
 
 use cortex_m_semihosting::hprintln;
-use hal::analog::adc::{Precision, SampleTime, VTemp};
+use hal::analog::adc::{OversamplingRatio, Precision, SampleTime, VTemp};
 use hal::prelude::*;
 use hal::stm32;
 use rt::entry;
@@ -26,19 +26,23 @@ fn main() -> ! {
     let mut adc = dp.ADC.constrain(&mut rcc);
     adc.set_sample_time(SampleTime::T_80);
     adc.set_precision(Precision::B_12);
+    adc.set_oversamling_ratio(OversamplingRatio::X_16);
+    adc.set_oversamling_shift(16);
+    adc.oversamling_enable(true);
+
     delay.delay(20.us()); // Wait for ADC voltage regulator to stabilize
     adc.calibrate();
 
     let mut adc_pin = gpioa.pa0.into_analog();
+
     let mut vtemp = VTemp::new();
     vtemp.enable(&mut adc);
 
     loop {
-        let u_raw: u32 = adc.read(&mut adc_pin).expect("adc read failed");
         let temp: u32 = adc.read(&mut vtemp).expect("temperature read failed");
+        let u_raw: u32 = adc.read(&mut adc_pin).expect("adc read failed");
+        let u_mv = adc.read_voltage(&mut adc_pin).expect("adc read failed");
 
-        let u = u_raw.saturating_sub(32) as f32 / 4_096_f32 * 3.3;
-        let temp = temp / 42;
-        hprintln!("u: {:.2} V | t: {:?}°C", u, temp).unwrap();
+        hprintln!("U raw: {} | U: {} mV | t: {}°C", u_raw, u_mv, temp / 42).unwrap();
     }
 }

src/analog/adc.rs

@@ -1,4 +1,6 @@
 //! # Analog to Digital converter
+use core::ptr;
+
 use crate::gpio::*;
 use crate::rcc::Rcc;
 use crate::stm32::ADC;
@@ -104,6 +106,7 @@ pub struct Adc {
     sample_time: SampleTime,
     align: Align,
     precision: Precision,
+    vdda_mv: Option<u32>,
 }
 
 /// Contains the calibration factors for the ADC which can be reused with [`Adc::set_calibration()`]
@@ -121,6 +124,7 @@ impl Adc {
             sample_time: SampleTime::T_2,
             align: Align::Right,
             precision: Precision::B_12,
+            vdda_mv: None,
         }
     }
 
@@ -223,6 +227,41 @@ impl Adc {
         self.rb.ier.modify(|_, w| w.eocie().clear_bit()); // end of sequence interupt disable
     }
 
+    pub fn read_voltage<PIN: Channel<Adc, ID = u8>>(
+        &mut self,
+        pin: &mut PIN,
+    ) -> nb::Result<u16, ()> {
+        let vdda_mv = if let Some(vdda_mv) = self.vdda_mv {
+            vdda_mv
+        } else {
+            let mut vref = VRef::new();
+            let vref_val: u32 = if vref.enabled(self) {
+                self.read(&mut vref)?
+            } else {
+                vref.enable(self);
+                let vref_val = self.read(&mut vref)?;
+                vref.disable(self);
+                vref_val
+            };
+
+            let vref_cal: u32 = unsafe {
+                // DS12766 3.13.2
+                ptr::read_volatile(0x1FFF_75AA as *const u16) as u32
+            };
+
+            // RM0454 14.9 Calculating the actual VDDA voltage using the internal reference voltage
+            // V_DDA = 3 V x VREFINT_CAL / VREFINT_DATA
+            let vdda_mv = vref_cal * 3_000_u32 / vref_val;
+            self.vdda_mv = Some(vdda_mv);
+            vdda_mv
+        };
+
+        self.read(pin).map(|raw: u32| {
+            let adc_mv = (vdda_mv * raw) >> 12;
+            adc_mv as u16
+        })
+    }
+
     pub fn release(self) -> ADC {
         self.rb
     }
@@ -375,6 +414,10 @@ macro_rules! int_adc {
                 pub fn disable(&mut self, adc: &mut Adc) {
                     adc.rb.ccr.modify(|_, w| w.$en().clear_bit());
                 }
+
+                pub fn enabled(&self, adc: &Adc) -> bool {
+                    adc.rb.ccr.read().$en().bit_is_set()
+                }
             }
 
             impl Default for $Chan {
@@ -394,6 +437,12 @@ macro_rules! int_adc {
     };
 }
 
+int_adc! {
+    VTemp: (12, tsen),
+    VRef: (13, vrefen),
+    VBat: (14, vbaten),
+}
+
 macro_rules! adc_pin {
     ($($Chan:ty: ($pin:ty, $chan:expr)),+ $(,)*) => {
         $(
@@ -406,12 +455,6 @@ macro_rules! adc_pin {
     };
 }
 
-int_adc! {
-    VTemp: (12, tsen),
-    VRef: (13, vrefen),
-    VBat: (14, vbaten),
-}
-
 adc_pin! {
     Channel0: (gpioa::PA0<Analog>, 0u8),
     Channel1: (gpioa::PA1<Analog>, 1u8),