Noise source initialization that is post-RNG.begin()

libraries/Crypto/NoiseSource.cpp

@@ -82,6 +82,21 @@ NoiseSource::~NoiseSource()
  * \sa calibrating(), output()
  */
 
+/**
+ * \brief Called when the noise source is added to RNG with
+ * \link RNGClass::addNoiseSource() RNG.addNoiseSource()\endlink.
+ *
+ * This function is intended for noise source initialization tasks that
+ * must be performed after \link RNGClass::begin() RNG.begin()\endlink
+ * has been called to initialize the global random number pool.
+ * For example, if the noise source has a unique identifier or serial
+ * number then this function can stir it into the pool at startup time.
+ */
+void NoiseSource::added()
+{
+    // Nothing to do here.
+}
+
 /**
  * \brief Called from subclasses to output noise to the global random
  * number pool.

libraries/Crypto/NoiseSource.h

@@ -35,6 +35,8 @@ public:
     virtual bool calibrating() const = 0;
     virtual void stir() = 0;
 
+    virtual void added();
+
 protected:
     virtual void output(const uint8_t *data, size_t len, unsigned int credit);
 };

libraries/Crypto/RNG.cpp

@@ -249,8 +249,10 @@ void RNGClass::begin(const char *tag, int eepromAddress)
 void RNGClass::addNoiseSource(NoiseSource &source)
 {
     #define MAX_NOISE_SOURCES (sizeof(noiseSources) / sizeof(noiseSources[0]))
-    if (count < MAX_NOISE_SOURCES)
+    if (count < MAX_NOISE_SOURCES) {
         noiseSources[count++] = &source;
+        source.added();
+    }
 }
 
 /**