From 5a543918ca0e79a41b2d724b7bf60716f8bc1bb0 Mon Sep 17 00:00:00 2001
From: George Beckstein <donbeckstein@live.com>
Date: Wed, 19 Feb 2020 13:27:08 -0500
Subject: [PATCH] Added API to reconfigure ADC reference voltage at runtime.

---
 drivers/AnalogIn.h          | 14 ++++++++++++++
 drivers/mbed_lib.json       |  4 ++--
 drivers/source/AnalogIn.cpp | 10 +++++++---
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/AnalogIn.h b/drivers/AnalogIn.h
index 0b04b5c1ac..ed6c14b69d 100644
--- a/drivers/AnalogIn.h
+++ b/drivers/AnalogIn.h
@@ -103,6 +103,17 @@ public:
      */
     float read_volts();
 
+    /**
+     * Sets this ADC instance's reference voltage.
+     *
+     * Defaults to the configurable MBED_CONF_DRIVERS_DEFAULT_ADC_VREF setting.
+     *
+     * The ADC's reference voltage is used to scale the output when calling AnalogIn::read_volts
+     *
+     * @param[in] vref New ADC reference voltage for this ADC instance.
+     */
+    void set_reference_voltage(float vref);
+
     /** An operator shorthand for read()
      *
      * The float() operator can be used as a shorthand for read() to simplify common code sequences
@@ -141,6 +152,9 @@ protected:
 
     analogin_t _adc;
     static SingletonPtr<PlatformMutex> _mutex;
+
+    float vref;
+
 #endif //!defined(DOXYGEN_ONLY)
 
 };
diff --git a/drivers/mbed_lib.json b/drivers/mbed_lib.json
index 8caeebad2c..6da6230979 100644
--- a/drivers/mbed_lib.json
+++ b/drivers/mbed_lib.json
@@ -42,8 +42,8 @@
             "help": "QSPI chip select pin",
             "value": "QSPI_FLASH1_CSN"
         },
-        "adc_vref": {
-            "help": "Reference voltage for ADC (float)",
+        "default_adc_vref": {
+            "help": "Default reference voltage for ADC (float)",
             "value": 3.3f
     }
 }
diff --git a/drivers/source/AnalogIn.cpp b/drivers/source/AnalogIn.cpp
index 084930f4ec..1370a71863 100644
--- a/drivers/source/AnalogIn.cpp
+++ b/drivers/source/AnalogIn.cpp
@@ -23,14 +23,14 @@ namespace mbed {
 
 SingletonPtr<PlatformMutex> AnalogIn::_mutex;
 
-AnalogIn::AnalogIn(PinName pin)
+AnalogIn::AnalogIn(PinName pin) : vref(MBED_CONF_DRIVERS_DEFAULT_ADC_VREF)
 {
     lock();
     analogin_init(&_adc, pin);
     unlock();
 }
 
-AnalogIn::AnalogIn(const PinMap &pinmap)
+AnalogIn::AnalogIn(const PinMap &pinmap) : vref(MBED_CONF_DRIVERS_DEFAULT_ADC_VREF)
 {
     lock();
     analogin_init_direct(&_adc, &pinmap);
@@ -56,7 +56,11 @@ unsigned short AnalogIn::read_u16()
 
 float AnalogIn::read_volts() {
     float ret = this->read();
-    return (ret*MBED_CONF_DRIVERS_ADC_VREF);
+    return (ret*this->vref);
+}
+
+void AnalogIn::set_reference_voltage(float vref) {
+    this->vref = vref;
 }
 
 } // namespace mbed