Configuration of the calendar using the RTC HAL API.
At the beginning of the main program the HAL_Init() function is called to reset all the peripherals, initialize the Flash interface and the systick. Then the SystemClock_Config() function is used to configure the system clock (SYSCLK) to run at 48 MHz.
The RTC peripheral configuration is ensured by the HAL_RTC_Init() function. This later is calling the HAL_RTC_MspInit()function which core is implementing the configuration of the needed RTC resources according to the used hardware (CLOCK, PWR, RTC clock source and BackUp). You may update this function to change RTC configuration.
LSE oscillator clock is used as RTC clock source.
The user can use also LSE as RTC clock source.
The user uncomment the adequate line on the main.h file.
@code
#define RTC_CLOCK_SOURCE_LSI
/* #define RTC_CLOCK_SOURCE_LSE */
@endcode
Open the ioc file with STM32CubeMX and select :
LSE as “Crystal/Ceramic Resonator” in RCC configuration.
LSE as RTC clock source in Clock configuration.
Generate code
LSI oscillator clock is delivered by a 32 kHz.
LSE (when available on board) is delivered by a 32.768 kHz crystal.
HAL_RTC_SetTime()and HAL_RTC_SetDate() functions are then called to initialize the time and the date.
A key value is written in backup data register 1 to indicate if the RTC is already configured.
The program behaves as follows:
After startup the program checks the Initialization status flag (INITS). This bit is set by hardware when the calendar year field is different from 0
INITS is reset : Calendar has not been initialized, the RTC is configured.
INITS is set: Calendar has been initialized and you can watch the time and the date on the debugger watch window.
When a reset occurs the RTC configuration is lost.
LED1 is turned ON when the RTC configuration is done correctly.
The current time and date are updated and displayed on the debugger in aShowTime and aShowDate variables.
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.
The application need to ensure that the SysTick time base is always set to 1 millisecond to have correct HAL operation.
System, RTC, Calendar, Reset
In order to make the program work, you must do the following :