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