#define GPIU 5
uint32_t Freq =0;

void setup() {
  pinMode(GPIU, OUTPUT);
  Serial.begin(115200);
  setCpuFrequencyMhz(10);
  Freq = getCpuFrequencyMhz();
  Serial.print(("Cpu Freq = "));
  Serial.println(Freq);
  Serial.println(" MHz");
  Freq = getXtalFrequencyMhz();
  Serial.print("Xtal Freq =");
  Serial.println(Freq);
  Serial.println(" MHz");
  Freq = getApbFrequency();
  Serial.print("Apb Freq = ");
  Serial.println(Freq);
  Serial.println(" MHz");
}

void loop() {
  digitalWrite(GPIU,1);
  digitalWrite(GPIU,0);
}