/**
@page RTC_LSI RTC prescaler adjustment with LSI Measurements example
@verbatim
******************************************************************************
* @file RTC/RTC_LSI/readme.txt
* @author MCD Application Team
* @brief Description of the RTC prescaler adjustment with LSI Measurements example.
******************************************************************************
*
* Copyright (c) 2020 STMicroelectronics. All rights reserved.
*
* This software component is licensed by ST under BSD 3-Clause license,
* the "License"; You may not use this file except in compliance with the
* License. You may obtain a copy of the License at:
* opensource.org/licenses/BSD-3-Clause
*
******************************************************************************
@endverbatim
@par Example Description
Use of the LSI clock source autocalibration to get a precise RTC clock.
In the associated software, the system clock is set to 48 MHz.
As an application example, it demonstrates how to configure the TIM16 timer
internally connected to LSI clock output, in order to adjust the RTC prescaler.
The Low Speed Internal (LSI) clock is used as RTC clock source.
After reset, the RTC prescaler is set with the default LSI frequency (32 kHz).
The RTC WakeUp is configured to generate an interrupt each 1s.
A key value is written in backup data register 1 to indicate if the wakeup timer has
already been enabled. If so the wakeup timer is disabled prior configuring the RTC
automatic wakeup.
LED2 is toggled inside the RTC WakeUp interrupt each 1s.
The inaccuracy of the LSI clock causes the RTC WakeUp Interrupt to be inaccurate.
The RTC CK_SPRE signal can be monitored by LED2 which is toggled into the RTC
Wakeup interrupt service routine.
The program waits until User push-button (B1) is pressed to begin the auto calibration.
Procedure:
- Configure the TIM16 to remap internally the TIM16 TIM_CHANNEL_1
Input Capture to the LSI clock output.
- Enable the TIM16 Input Capture interrupt: after one cycle of LSI clock, the
period value is stored in a variable and compared to the HCLK clock to get
its real value.
- The RTC prescaler is adjusted with this LSI frequency value so that the RTC
CK_SPRE value become more accurate.
- When calibration is done the variable uwLsiFreq is visualized into the debugger
to indicate the end of this operation.
- The LSI value is updated and displayed on the debugger in uwLsiFreq variable.
- LED3 is On: This indicates that the system generates an error.
@note Care must be taken when using HAL_Delay(), this function provides accurate
delay (in milliseconds) based on variable incremented in SysTick ISR. This
implies that if HAL_Delay() is called from a peripheral ISR process, then
the SysTick interrupt must have higher priority (numerically lower)
than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
@note The application need to ensure that the SysTick time base is always set to 1 millisecond
to have correct HAL operation.
@par Keywords
System, RTC, LSI, Internal time stamp, Wake up, interrupt
@par Directory contents
- RTC/RTC_LSI/Inc/stm32wlxx_nucleo_conf.h BSP configuration file
- RTC/RTC_LSI/Inc/stm32wlxx_hal_conf.h HAL configuration file
- RTC/RTC_LSI/Inc/main.h Header file for main.c
- RTC/RTC_LSI/Inc/stm32wlxx_it.h Header for stm32wlxx_it.c
- RTC/RTC_LSI/Src/system_stm32wlxx.c STM32WLxx system clock configuration file
- RTC/RTC_LSI/Src/stm32wlxx_it.c Interrupt handlers
- RTC/RTC_LSI/Src/main.c Main program
- RTC/RTC_LSI/Src/stm32wlxx_hal_msp.c HAL MSP module
@par Hardware and Software environment
- This example runs on STM32WL55JCIx devices.
- This example has been tested with NUCLEO-WL55JC RevC board and can be
easily tailored to any other supported device and development board.
- NUCLEO-WL55JC RevC Set-up
- Use LED2 connected to PB.09 pin (pin 26 in CN10 connector).
- Use the User push-button (B1) connected to pin PA.00 (External line 0)
@par How to use it ?
In order to make the program work, you must do the following :
- Open your preferred toolchain
- Rebuild all files and load your image into target memory
- Run the example
* <h3><center>© COPYRIGHT STMicroelectronics</center></h3>
*/
378e461e46