STM32G474 clock 170 MHz

[koyocik]

Hello,

I use 25 MHz quarz (XRCGB25M000FAN00R0) together with 5.6 pF load capacitors. When I configure clock to 170MHz my program stuck here: while (READ_BIT(RCC->CR, RCC_CR_PLLRDY) == 0U).

When I configure clock to 168.75 MHz, then everything work corectly. 

Can someone explain how this problem could be solved?

Thank you for answers.

Best regards

Configuration for 168.75MHz clock:

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1_BOOST);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = RCC_PLLM_DIV2;
  RCC_OscInitStruct.PLL.PLLN = 27;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;
  RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
  {
    Error_Handler();
  }
}

 Configuration for 170 MHz clock:

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1_BOOST);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = RCC_PLLM_DIV5;
  RCC_OscInitStruct.PLL.PLLN = 68;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;
  RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
  {
    Error_Handler();
  }
}

[mƎALLEm]

Hello,

That's strange.  I don't see any issue in your clock init.

Are you sure you have 25MHz on the OSC_IN/OSC_OUT pins?

How did you calculate the load capacitors of 5.6 pF? 

[koyocik]

I used this equation: C1, C2 = 2*CL – 2*Cstray. 

I tried use bigger capacitor value and lower but without any good result.

Quarz is connected to pins 19 and 20 like below.

[mƎALLEm]

What CL and Cs values you have used for the calculation?

[koyocik]

CL from datasheet is 6pF and as Cs I took 3.2pF.

[mƎALLEm]

But to my knowledge Cs calculation needs to include CI/O (pin capacitance):

From the AN2867:

From the G4 datasheet:

[koyocik]

I used this page for calculations:

https://blog.adafruit.com/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/

If, I take capacitance from you, then I get for C1 and C2 2pF value. But the problem still exists.

When I measure crystal frequency (with 2 pF capacitors) with scope I get 25MHz on pin 19 (OSC_IN), but when I measure frequency on pin 20 (OSC_OUT) I get about 19 MHz. It is normal?

My µc booted normal (only in debug mode stuck in clock configuration). After starts I try call function HAL_NVIC_SystemReset(), but nothing happens. I read that no reaction on system reset could be also caused by clock configuration. 

[Ozone]

Apart from the capacitance issue discussed, there is an obvious difference in the PLLM and PLLN values for both cases.
Check the datasheet that you don't exceed the maximal PLL frequency with your 170 MHz settings.

[koyocik]

I used CubeMX for clock configuration. Do you think that code is wrong generated?

[koyocik]

I found in datasheet that PLL input clock for my STM32G747 can be maximal 16MHz. It means, that I can't use 25MHz crystal to run with my µC ?