FreeRTOS CPU HSE Clock Configuration

[EG-Julien]

Hello everyone, I'm using an STM32F303CCT6 to control a TMC5160, a W5500 and some other stuffs. I'm using the STM32Duino FreeRTOS lib with the Arduino frameworks (In Platform IO, I'm not sure if it's a bug from PIO nor the lib ...). Everything is working fine except the clock system ... The max CPU frequency achievable is 72 MHz. I have a 32 MHz HSE on my board (homemade), I have generated my SystemClockConfig function with STM32CubeMX.

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

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_LSI
                              |RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV4;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.LSIState = RCC_LSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  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_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB|RCC_PERIPHCLK_USART1
                              |RCC_PERIPHCLK_USART2|RCC_PERIPHCLK_I2C1
                              |RCC_PERIPHCLK_RTC;
  PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_SYSCLK;
  PeriphClkInit.Usart2ClockSelection = RCC_USART2CLKSOURCE_SYSCLK;
  PeriphClkInit.I2c1ClockSelection = RCC_I2C1CLKSOURCE_HSI;
  PeriphClkInit.RTCClockSelection = RCC_RTCCLKSOURCE_LSI;
  PeriphClkInit.USBClockSelection = RCC_USBCLKSOURCE_PLL_DIV1_5;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    Error_Handler();
  }
}

If I check HSE_IN with an oscilloscope I have my 32MHz, as soon as I remove the code above, my crystal stops running as expected. I would say that my clock hardware is fine.

Now, I have just created a dummy sketch to test things:

static void vTask( void * pvParameters)
{
  vTaskDelay(1);

  while (true)
  {
    SerialUSB.println(millis());
    SerialUSB.println(HAL_RCC_GetHCLKFreq()); // return 180 000 000, but should be 72 000 000 ?
    vTaskDelay(1000 / portTICK_PERIOD_MS); // should be a 1 sec delay, but it is rather a 100ms one ...
  }

}

void setup()
{
  SystemCoreClock = 72000000; // it has the same behavior with or without this.
  SystemCoreClockUpdate();

  SerialUSB.begin(115200);
  while (!SerialUSB);

  delay(1000);

  xTaskCreate(vTask, "task1", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL);

  vTaskStartScheduler();

}

void loop()
{
  ;
}

This is the first time I'm playing with CPU clocks frequencies. I'm pretty sure I missed something in the documentation.

I tried:

• Put board_build.f_cpu = 72000000 in the platformio.ini but I read that it's reserved for esp, isn't it ? And it doesn't work anyway, The task is still running 10 times a second;
• Modify system_stm32f3xx.h to write SystemCoreClock = 72000000;
• Re-write configCPU_CLOCK_HZ in my STM32FreeRTOSConfig_extra.h;
• Re-write configTICK_RATE_HZ in my STM32FreeRTOSConfig_extra.h;

Nothing worked for now. If anyone has any idea, or documentation that I might have missed ... Thanks for your help !

I've posted this on PIO forum too

[EG-Julien]

Adding: -D HSE_VALUE=32000000 to build flags solve the problems.

Final main.cpp:

static void vTask( void * pvParameters )
{
  vTaskDelay(1);

  while (true)
  {
    SerialUSB.println(millis());
    SerialUSB.println(HAL_RCC_GetHCLKFreq());
    vTaskDelay(1000 / portTICK_PERIOD_MS);
  }

}

void setup()
{
  SerialUSB.begin(115200);
  while (!SerialUSB);

  delay(1000);

  xTaskCreate(vTask, "task1", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL);

  vTaskStartScheduler();

}

void loop()
{
  ;
}

Final platformio.ini:

[env:genericSTM32F303CC]
platform = ststm32
board = genericSTM32F303CC
framework = arduino
lib_deps = stm32duino/STM32duino FreeRTOS@^10.3.2

board_build.f_cpu = 72000000

build_flags =
    -fexceptions
    -D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC
    -D USBCON
;    -D USBD_USE_CDC
    -D HAL_PCD_MODULE_ENABLED
    -D HSE_VALUE=32000000

upload_protocol = stlink