[PHY] Added TRNG support (#178)

src/protocols/PhysicalLayer/PhysicalLayer.cpp

@@ -143,3 +143,27 @@ int16_t PhysicalLayer::receive(String& str, size_t len) {
 float PhysicalLayer::getFreqStep() const {
   return(_freqStep);
 }
+
+int32_t PhysicalLayer::random(int32_t max) {
+  if(max == 0) {
+    return(0);
+  }
+
+  // get random bytes from the radio
+  uint8_t randBuff[4];
+  for(uint8_t i = 0; i < 4; i++) {
+    randBuff[i] = random();
+  }
+
+  // create 32-bit TRNG number
+  int32_t randNum = ((int32_t)randBuff[0] << 24) | ((int32_t)randBuff[1] << 16) | ((int32_t)randBuff[2] << 8) | ((int32_t)randBuff[3]);
+  return(randNum % max);
+}
+
+int32_t PhysicalLayer::random(int32_t min, int32_t max) {
+  if(min >= max) {
+    return(min);
+  }
+
+  return(PhysicalLayer::random(max - min) + min);
+}

src/protocols/PhysicalLayer/PhysicalLayer.h

@@ -216,7 +216,7 @@ class PhysicalLayer {
     float getFreqStep() const;
 
     /*!
-     \brief Query modem for the packet length of received payload.
+     \brief Query modem for the packet length of received payload. Must be implemented in module class.
 
      \param update Update received packet length. Will return cached value when set to false.
 
@@ -224,6 +224,33 @@ class PhysicalLayer {
    */
    virtual size_t getPacketLength(bool update = true) = 0;
 
+   /*!
+    \brief Get truly random number in range 0 - max.
+
+    \param max The maximum value of the random number (non-inclusive).
+
+    \returns Random number.
+   */
+   int32_t random(int32_t max);
+
+   /*!
+    \brief Get truly random number in range min - max.
+
+    \param min The minimum value of the random number (inclusive).
+
+    \param max The maximum value of the random number (non-inclusive).
+   
+    \returns Random number.
+   */
+   int32_t random(int32_t min, int32_t max);
+
+   /*!
+    \brief Get one truly random byte from RSSI noise. Must be implemented in module class.
+
+    \returns TRNG byte.
+  */
+   virtual uint8_t random() = 0;
+
 #ifndef RADIOLIB_GODMODE
   private:
 #endif