#define GPIO_pin 5
uint32_t Freq = 0;
void setup()
{
  pinMode(GPIO_pin, OUTPUT);
  Serial.begin(115200);
  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);
}