Run STM32F103 from internal oscillator with PlatformIO (Arduino)?

I dug around a bit in the PlatformIO directory.

The following paths are for "generic":

• C:\Users\<user>\.platformio\platforms\ststm32\boards\genericSTM32F103C8.json
• C:\Users\<user>\.platformio\packages\framework-arduinoststm32\variants\Generic_F103Cx\variant.cpp

Define your own system clock configuration in e.g. your main.cpp:

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

  /* Initializes the CPU, AHB and APB busses clocks */
  // RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  // RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  // RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  // RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI_DIV2;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
    while (1);
  }

  /* Initializes the CPU, AHB and APB busses 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) {
    while (1);
  }

  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC ;
  PeriphClkInit.AdcClockSelection = RCC_ADCPCLK2_DIV6;
  PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_PLL_DIV1_5;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK) {
    while (1);
  }
}

The ini then is:

[env:bluepill_f103c8]
platform = ststm32
board = genericSTM32F103C8
framework = arduino
upload_protocol = stlink
lib_deps = olikraus/U8g2 @ ^2.28.7

I'd recommend renaming the env to avoid confusion.

I have not yet verified the actual clock speed.