I am using STM32L0 and I want to run RTC in my custom board. I using Internal LSI clock for RTC. When I set Alarm for 60 sec it is generated in around 54 sec so i think RTC is running faster . So how can i calibrate it?

[SPraj.1]

void SystemClock_Config(void)

{

 RCC_OscInitTypeDef RCC_OscInitStruct = {0};

 RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

 RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};

 /** Configure the main internal regulator output voltage

 */

 __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);

 /** 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.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_HSI;

 RCC_OscInitStruct.PLL.PLLMUL = RCC_PLLMUL_3;

 RCC_OscInitStruct.PLL.PLLDIV = RCC_PLLDIV_3;

 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_HSE;

 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_1) != HAL_OK)

 {

  Error_Handler();

 }

 PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1|RCC_PERIPHCLK_I2C1

               |RCC_PERIPHCLK_RTC|RCC_PERIPHCLK_USB;

 PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK2;

 PeriphClkInit.I2c1ClockSelection = RCC_I2C1CLKSOURCE_PCLK1;

 PeriphClkInit.RTCClockSelection = RCC_RTCCLKSOURCE_LSI;

 PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_PLL;

 if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)

 {

  Error_Handler();

 }

}

Ams this ias code of RTC.c

[waclawek.jan]

LSI is a very imprecise clock source, see datasheet. You can "calibrate" it by changing the asynchronous and synchronous pedalers, but it will never be stable and precise.

JW

[SPraj.1]

so what is the best option to go with?

[waclawek.jan]

Best option for what?

To maintain real time, you need to use LSE and a 32.768kHz crystal.

If you have a crystal on HSE and you don't want to use some of the low-power modes (in some of which LSI doesn't work either, btw.), you can derive the RTC clock from HSE too.

JW