#define GPIO_pin 5
uint32_t Freq =0;
void setup()
{
  pinMode(GPIO_pin,OUTPUT);
  Serial.begin(115200);
  setCpuFrequencyMhz(10);
  Freq = getCpuFrequencyMhz();
  Serial.print("CPU Freq =");
  Serial.print(Freq);
  Serial.println("MHz");
  Freq =getXtalFrequencyMhz();
  Serial.print("XTAL Freq = ");
  Serial.print(Freq);
  Serial.println("Mhz");
  Freq = getApbFrequency();
  Serial.print("APB Freq =");
  Serial.print(Freq);
  Serial.println("Hz");
}
void loop()
{
  digitalWrite(GPIO_pin, 1);
  digitalWrite(GPIO_pin, 0);
}