#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);
}