Enable trng support for STM32H7 boards

Author: pennam

Diff for: cores/arduino/WMath.cpp

@@ -23,10 +23,36 @@
 
 extern "C" {
   #include "stdlib.h"
+  #include "hal/trng_api.h"
 }
 
+#if defined(ARDUINO_PORTENTA_H7_M7) || \
+    defined(ARDUINO_NICLA_VISION) || \
+    defined(ARDUINO_OPTA) || \
+    defined(ARDUINO_GIGA)
+#define MBED_TRNG_SUPPORT 1
+static long trng()
+{
+  trng_t trng_obj;
+  trng_init(&trng_obj);
+  long value;
+  size_t olen;
+  if (trng_get_bytes(&trng_obj, (uint8_t*)&value, sizeof(value), &olen) != 0)
+    return -1;
+  trng_free(&trng_obj);
+  return value >= 0 ? value : -value;
+}
+#endif
+
+#if (MBED_TRNG_SUPPORT == 1)
+static bool useTRNG = true;
+#endif
+
 void randomSeed(unsigned long seed)
 {
+#if (MBED_TRNG_SUPPORT == 1)
+  useTRNG = false;
+#endif
   if (seed != 0) {
     srandom(seed);
   }
@@ -37,6 +63,11 @@ long random(long howbig)
   if (howbig == 0) {
     return 0;
   }
+#if (MBED_TRNG_SUPPORT == 1)
+  if (useTRNG == true) {
+    return trng() % howbig;
+  }
+#endif
   return random() % howbig;
 }
 
@@ -48,3 +79,5 @@ long random(long howsmall, long howbig)
   long diff = howbig - howsmall;
   return random(diff) + howsmall;
 }
+
+#undef MBED_TRNG_SUPPORT