Hi.I am using stm32l496 but systick every 20s There is a difference of 20ms.I paste my code and clock config in stm32cube.

[alianvari]

void SystemClock_Config(void)

{

 RCC_OscInitTypeDef RCC_OscInitStruct = {0};

 RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

 RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};

 /** Initializes the CPU, AHB and APB busses clocks 

 */

 RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSI|RCC_OSCILLATORTYPE_MSI;

 RCC_OscInitStruct.LSIState = RCC_LSI_ON;

 RCC_OscInitStruct.MSIState = RCC_MSI_ON;

 RCC_OscInitStruct.MSICalibrationValue = 0;

 RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_8;

 RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;

 if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)

 {

  Error_Handler();

 }

 /** 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_MSI;

 RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV8;

 RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;

 RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

 if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)

 {

  Error_Handler();

 }

 PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1|RCC_PERIPHCLK_LPTIM1;

 PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK2;

 PeriphClkInit.Lptim1ClockSelection = RCC_LPTIM1CLKSOURCE_LSI;

 if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure the main internal regulator output voltage 

 */

 if (HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1) != HAL_OK)

 {

  Error_Handler();

 }

}

[S.Ma]

What is the clock LSI tolerance spec in %?

What is the clock error of 20msec vs 20 sec?

[alianvari]

The micro prints a sentence once every 20 seconds,By comparing the printing time of the sentences I find that:

Time interval of 2 printed words of 20 seconds,It takes about 20 seconds and 20 milliseconds.

[Tesla DeLorean]

The MSI is pretty sloppy. Things with timing criticality like CAN, USB or Ethernet need a crystal, and Radio a TCXO.​