message: Tympan: make FreeRam() work for Teensy4
diff: @@ -343,9 +343,17 @@ class TympanBase : public AudioControlAIC3206, public Print
  }
  }
  - int FreeRam() {
  + static int FreeRam(void) {
  + #if defined(__IMXRT1062__)
  + extern unsigned long _heap_start;
  + extern unsigned long _heap_end;
  + extern char *__brkval;
  +
  + return (char *)&_heap_end - __brkval;
  + #else
  char top; //this new variable is, in effect, the mem location of the edge of the heap
  return &top - reinterpret_cast<char*>(sbrk(0));
  + #endif
  }
  void printCPUandMemoryMessage(void) {
  print("CPU Cur/Pk: ");
  