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