use fsr enum

src/libDevCom/ADS1015.cpp

 #include "ADS1015.h"
 
 // std/stl
-#include <algorithm>  // std::find
+#include <algorithm>  // std::find, std::find_if
 #include <chrono>
 #include <iomanip>
 #include <sstream>
@@ -121,7 +121,7 @@ void ADS1015::configSingleShot(uint16_t& config) {
 void ADS1015::configPGA(uint16_t& config) {
     // configure programmable gain amplifier based on the configured voltage
     // reference
-    Gain gain = fsrToGainMap.at(m_fullscale_range);
+    Gain gain = gainFromFSR(m_fullscale_range);
     config |= static_cast<uint16_t>(gainToConfigMap.at(gain));
 }
 
@@ -215,3 +215,17 @@ bool ADS1015::conversionComplete() {
         m_com->read_reg16(static_cast<uint16_t>(Address::POINTER_CONFIG));
     return (reg & 0x8000) != 0;
 }
+
+ADS1015::Gain ADS1015::gainFromFSR(FullScaleRange range) {
+
+    auto it = std::find_if(gainToFSRMap.begin(), gainToFSRMap.end(),
+            [&range](const std::pair<Gain, FullScaleRange>& item) {
+                            return item.second == range;
+                    });
+
+    // shouldn't happen
+    if(it == gainToFSRMap.end()) {
+        throw std::runtime_error("Invalid FullScaleRange value");
+    }
+    return it->first;
+}

src/libDevCom/ADS1015.h

@@ -128,6 +128,9 @@ class ADS1015 : public ADCDevice {
  private:
     void init(FullScaleRange full_scale_range, std::shared_ptr<I2CCom> com);
 
+    std::shared_ptr<I2CCom> m_com;
+    std::shared_ptr<LinearCalibration> m_calibration;
+
     enum class Address : uint16_t {
         POINTER_CONVERT = 0x00,
         POINTER_CONFIG = 0x01,
@@ -213,6 +216,15 @@ class ADS1015 : public ADCDevice {
         {Gain::xEIGHT, FullScaleRange::FSR_0_512},
         {Gain::xSIXTEEN, FullScaleRange::FSR_0_256}};
 
+    // return the ADS1015::Gain associated with ADS1015::FullScaleRange
+    Gain gainFromFSR(FullScaleRange range);
+
+    // map to the actual gain value associated with ADS1015::FullScaleRange enum element
+    const std::map<FullScaleRange, double> fsrToValMap{
+        {FullScaleRange::FSR_6_144, 6.144}, {FullScaleRange::FSR_4_096, 4.096},
+        {FullScaleRange::FSR_2_048, 2.048}, {FullScaleRange::FSR_1_024, 1.024},
+        {FullScaleRange::FSR_0_512, 0.512}, {FullScaleRange::FSR_0_256, 0.256}};
+
     // map between programmable gain configuration and ADS1015 configuration
     // register values
     const std::map<Gain, Config> gainToConfigMap{
@@ -223,21 +235,6 @@ class ADS1015 : public ADCDevice {
         {Gain::xEIGHT, Config::CONFIG_PGA_8},
         {Gain::xSIXTEEN, Config::CONFIG_PGA_16}};
 
-    const std::map<FullScaleRange, double> fsrToValMap{
-        {FullScaleRange::FSR_6_144, 6.144}, {FullScaleRange::FSR_4_096, 4.096},
-        {FullScaleRange::FSR_2_048, 2.048}, {FullScaleRange::FSR_1_024, 1.024},
-        {FullScaleRange::FSR_0_512, 0.512}, {FullScaleRange::FSR_0_256, 0.256}};
-
-    const std::map<FullScaleRange, Gain> fsrToGainMap{
-        {FullScaleRange::FSR_6_144, Gain::xTWOTHIRDS},
-        {FullScaleRange::FSR_4_096, Gain::xONE},
-        {FullScaleRange::FSR_2_048, Gain::xTWO},
-        {FullScaleRange::FSR_1_024, Gain::xFOUR},
-        {FullScaleRange::FSR_0_512, Gain::xEIGHT},
-        {FullScaleRange::FSR_0_256, Gain::xSIXTEEN}};
-
-    std::shared_ptr<I2CCom> m_com;
-    std::shared_ptr<LinearCalibration> m_calibration;
 
     // Note that for ADS1015, single-ended mode has 11-bit resolution (max val =
     // 0x7ff). Only when performing differential measurements do you get the
@@ -248,7 +245,6 @@ class ADS1015 : public ADCDevice {
 
     // some helper methods
     bool conversionComplete();
-    Gain fsrToGain(FullScaleRange fsr);
 
     // methods for configuring the ADS1015
     void configSingleShot(uint16_t& config);