add temp/vref controls

Author: fuchsnj

CHANGELOG.md

@@ -46,6 +46,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `Serial` support for UART4/5
 - Allow to set HSE bypass bit in `RCC` clock configuration register to use an external clock input on the `OSC_IN` pin [#485]
 - initial support of `embedded-hal-1.0` [#416]
+- Added ADC methods for temp/vref sensor control. The time required for reading from the ADC can be reduced using these [#422]
 - Add tools/check.py python script for local check [#467]
 - Add changelog check on PRs [#467]
 - Reexport `Direction` from `qei` [#479]
@@ -56,6 +57,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Add enable/disable EOC interrupt functions for ADCs [#526]
 
 [#416]: https://github.com/stm32-rs/stm32f1xx-hal/pull/416
+[#422]: https://github.com/stm32-rs/stm32f1xx-hal/pull/422
 [#453]: https://github.com/stm32-rs/stm32f1xx-hal/pull/453
 [#462]: https://github.com/stm32-rs/stm32f1xx-hal/pull/462
 [#467]: https://github.com/stm32-rs/stm32f1xx-hal/pull/467

src/adc.rs

@@ -18,6 +18,9 @@ use embedded_dma::WriteBuffer;
 use crate::pac::{self, RCC};
 use crate::pacext::adc::{AdcRB, Cr1W, Cr2R, Cr2W, Dr, ExtSelW};
 
+const TEMP_CHANNEL: u8 = 16;
+const VREF_CHANNEL: u8 = 17;
+
 /// Continuous mode
 pub struct Continuous;
 /// Scan mode
@@ -497,7 +500,29 @@ where
 
 impl Adc<pac::ADC1> {
     fn read_aux(&mut self, chan: u8) -> u16 {
-        let tsv_off = if self.rb.cr2().read().tsvrefe().bit_is_clear() {
+        let tsv_enabled = if matches!(chan, TEMP_CHANNEL | VREF_CHANNEL) {
+            self.enable_temp_vref()
+        } else {
+            false
+        };
+
+        let val = self.convert(chan);
+
+        if tsv_enabled {
+            self.disable_temp_vref();
+        }
+
+        val
+    }
+
+    /// Enables the temperature / VREF sensor.
+    ///
+    /// Enabling this before calling `read_temp` or `read_vref` will speed up the reading
+    /// since you won't have to wait for the sensor to start up.
+    ///
+    /// Returns true if the sensor was previously off.
+    pub fn enable_temp_vref(&mut self) -> bool {
+        if !self.is_temp_vref_enabled() {
             self.rb.cr2().modify(|_, w| w.tsvrefe().set_bit());
 
             // The reference manual says that a stabilization time is needed after the powering the
@@ -508,15 +533,19 @@ impl Adc<pac::ADC1> {
             true
         } else {
             false
-        };
-
-        let val = self.convert(chan);
-
-        if tsv_off {
-            self.rb.cr2().modify(|_, w| w.tsvrefe().clear_bit());
         }
+    }
 
-        val
+    /// Disables the temperature / VREF sensor.
+    ///
+    /// `read_temp` and `read_vref` will still work with this disabled, but will take a
+    /// bit longer since you have to wait for the sensor to start up.
+    pub fn disable_temp_vref(&mut self) {
+        self.rb.cr2().modify(|_, w| w.tsvrefe().clear_bit());
+    }
+
+    pub fn is_temp_vref_enabled(&self) -> bool {
+        self.rb.cr2().read().tsvrefe().bit_is_set()
     }
 
     /// Temperature sensor is connected to channel 16 on ADC1. This sensor can be used
@@ -531,6 +560,9 @@ impl Adc<pac::ADC1> {
     /// temperature readings are needed, an external temperature sensor part should be used."
     ///
     /// Formula to calculate temperature value is also taken from the section 11.10.
+    ///
+    /// If the temp/VREF sensor is disabled, this will still work but must wait
+    /// for the sensor to start up. Call `enable_temp_vref` to speed this up.
     pub fn read_temp(&mut self) -> i32 {
         /// According to section 5.3.18 "Temperature sensor characteristics"
         /// from STM32F1xx datasheets, TS constants values are as follows:
@@ -556,8 +588,8 @@ impl Adc<pac::ADC1> {
         };
 
         self.set_sample_time(sample_time);
-        let val_temp: i32 = self.read_aux(16u8).into();
-        let val_vref: i32 = self.read_aux(17u8).into();
+        let val_temp: i32 = self.read_aux(TEMP_CHANNEL).into();
+        let val_vref: i32 = self.read_aux(VREF_CHANNEL).into();
         let v_sense = val_temp * 1200 / val_vref;
 
         self.restore_cfg(prev_cfg);
@@ -573,8 +605,11 @@ impl Adc<pac::ADC1> {
     /// For instance, reading from any ADC channel can be converted into voltage (mV)
     /// using the following formula:
     ///     v_chan = adc.read(chan) * 1200 / adc.read_vref()
+    ///
+    /// If the temp/VREF sensor is disabled, this will still work but must wait
+    /// for the sensor to start up. Call `enable_temp_vref` to speed this up.
     pub fn read_vref(&mut self) -> u16 {
-        self.read_aux(17u8)
+        self.read_aux(VREF_CHANNEL)
     }
 }