difference between real measured frequency and set frequency

[PetrK]

Hello,

I am dealing with difference between real measured frequency and set on my Nucleo H755ZI-Q.
the measured real frequency :
APB1 76,8 MHz
APB2 76,8 MHz
recalculated
debugging frequencz SWV Core Clock 153,6 MHz

I also try printf debuged frequency:
HSE is enabled and ready.
System Clock: 480000000 Hz
APB1 Timer Clock: 120000000 Hz
APB2 Timer Clock: 120000000 Hz
APB1 Prescaler: 4
APB2 Prescaler: 4

 if ((RCC->CR & RCC_CR_HSERDY) != 0) {
      printf("HSE is enabled and ready.\n");
  } else {
      printf("HSE is not enabled or ready.\n");
  }

  printf("System Clock: %lu Hz\n", HAL_RCC_GetSysClockFreq());
  printf("APB1 Timer Clock: %lu Hz\n", HAL_RCC_GetPCLK1Freq());
  printf("APB2 Timer Clock: %lu Hz\n", HAL_RCC_GetPCLK2Freq());


  uint32_t apb1_prescaler = (RCC->D2CFGR & RCC_D2CFGR_D2PPRE1) >> RCC_D2CFGR_D2PPRE1_Pos;
  uint32_t apb2_prescaler = (RCC->D2CFGR & RCC_D2CFGR_D2PPRE2) >> RCC_D2CFGR_D2PPRE2_Pos;

  printf("APB1 Prescaler: %lu\n", apb1_prescaler);
  printf("APB2 Prescaler: %lu\n", apb2_prescaler);

  uint32_t pclk1 = HAL_RCC_GetPCLK1Freq();  // Get APB1 clock
  uint32_t pclk2 = HAL_RCC_GetPCLK2Freq();  // Get APB2 clock

  printf("APB1 Clock: %lu Hz\n", pclk1);
  printf("APB2 Clock: %lu Hz\n", pclk2);

  // If prescaler > 1, Timer Clock = PCLK * 2
  if (apb1_prescaler > 3) {  // Values >3 mean prescaler is applied
      printf("APB1 Timer Clock: %lu Hz\n", pclk1 * 2);
  } else {
      printf("APB1 Timer Clock: %lu Hz\n", pclk1);
  }

  if (apb2_prescaler > 3) {
      printf("APB2 Timer Clock: %lu Hz\n", pclk2 * 2);
  } else {
      printf("APB2 Timer Clock: %lu Hz\n", pclk2);
  }

Does anyone have any suggestion what I am doing wrong?

Edited Code Format 

[Sarra.S]

Hello @PetrK, 

Given that the discrepancy is huge, in the order of 50MHz for APB1 and APB2, i suspect there is maybe an issue with the measurement method! 

[PetrK]

Hello @Sarra.S ,

thank you for the reply, I think that it is not measurement method - also have to set the timers regarding to the value ato be able run the servos. The real frequency is real.
I also have to add the 153.6 MHz into the SWV settings to get the printf values.  

Should it be some power issue? I am powering the Nucleo

through USB from notebook.

[MasterT]

In case of ambiguity, use hardware - oscilloscope verification driving MCO1 / MCO2 outputs, there 5 /6 control check points for each

[Sarra.S]

Hello @PetrK, any updates on this matter?