add getStep() method

src/ebusd/mqtthandler.cpp

@@ -1098,7 +1098,7 @@ void MqttHandler::run() {
                 values.set("max", ostr.str());
                 ostr.str("");
               }
-              if (dt->readFromRawValue(1, g_publishFormat, &ostr) != RESULT_OK) {
+              if (dt->getStep(g_publishFormat, &ostr) != RESULT_OK) {
                 // fallback method, when smallest number didn't work
                 int divisor = dt->getDivisor();
                 float step = 1.0f;

src/lib/ebus/datatype.cpp

@@ -735,6 +735,10 @@ result_t NumberDataType::getMinMax(bool getMax, const OutputFormat outputFormat,
   return readFromRawValue(getMax ? m_maxValue : m_minValue, outputFormat, output);
 }
 
+result_t NumberDataType::getStep(const OutputFormat outputFormat, ostream* output) const {
+  return readFromRawValue(hasFlag(EXP) ? floatToUint(1.0f) : 1, outputFormat, output);
+}
+
 result_t NumberDataType::readRawValue(size_t offset, size_t length, const SymbolString& input,
                                       unsigned int* value) const {
   size_t start = 0, count = length;

src/lib/ebus/datatype.h

@@ -517,6 +517,14 @@ class NumberDataType : public DataType {
    */
   result_t getMinMax(bool getMax, const OutputFormat outputFormat, ostream* output) const;
 
+  /**
+   * Get the smallest step value for increment/decrement.
+   * @param outputFormat the @a OutputFormat options to use.
+   * @param output the ostream to append the formatted value to.
+   * @return @a RESULT_OK on success, or an error code.
+   */
+  result_t getStep(const OutputFormat outputFormat, ostream* output) const;
+
   /**
    * @return the divisor (negative for reciprocal).
    */