版本 ce8887a52780f5e46945c48dd05dd8ed52bae5c5
Changes from ce8887a52780f5e46945c48dd05dd8ed52bae5c5 to 3a557f1cfe2c6c42cc3b54123f758c6afc705d1a
Introduction
=============
A real-time clock (RTC) is a computer clock that keeps track of the current time. RTCs are also present in almost any electronic device that requires accurate time keeping. The real-time clock (RTC) embedded in STM32 microcontrollers acts as an independent BCD timer/ counter.
Features
===============
- Calendar
- Alarm
- Auto wakeup
- Timestamp
- Tamper detection
- Programmable daylight saving time
- Didigal calibration
- Synchronization
- Synchronization by shifting
- Reference clock detection
- Backup register
- Alternative function IO
Clock Source
=============
LSI RC : 32 kHz
LSE OSC : 32.768 kHz
HSE OSC : 4-26 MHz
.. image:: /stm32F4 RTC clock source
Prescaler
=============
Prescaler generates the clock to update update the calendar.
To minimize power comsuption the prescaler is split into two prescalers, asynchronous and synchronous. It is recommended to configure the asynchronous prescaler to a high value to minimize consumption.
asynchronous prescaler clocks subsecond of calendar and propagate to synchronous prescaler to update date and time by second.
asynchronous prescaler clocks subsecond of calendar and propagates to synchronous prescaler to update date and time by second.
One can configure them through ``PREDIV_A`` and ``PREDIV_S`` bits in ``RTC_PRER``
Calendar
=============
A calendar keeps track of the date (day, week, month, year) and time (hours, minutes and seconds) and even subseconds. It manages of numbers of days of mouths automaticly. Daylight saving time adjustment is programmable by software.
Binary repersentation is in binary-coded decimal (BCD) format.
Data can be read indirectly from shadow registers or directly from connters. The former method delays some clocks but ensures consistency between date and time registers; the later is opposite but this is especially useful after exiting from low power modes, since the shadow registers are not updated during these modes.
Data, time, and subsecond corresponds to ``RTC_DR``, ``RTC_TR``, and ``RTC_SSR``. With ``BYPSHAD`` bit set, data can be read directly from counter.
Synchronization and Reference clock detection
====================================================
RTC can be synchronized to remote clock by adding a 'shift' to counter continuously to delay, or vice versa.
With reference clock detection, RTC shifts misaligned 1 Hz clock to align it with the nearst referenced edge (found in a given time window).
One can adjust time by configuring shift through ``RTC_SHIFTR``.
When reference clock detection is enabled (``REFCKON``), must not write ``RTC_SHIFTR`` and not enable calibration and set prescalers (``PREDIV_A`` and ``PREDIV_S``) to default.
Configuration
================
