/*!
    \file    readme.txt
    \brief   description of RTC clock calibration
    
    \version 2026-02-03, V1.6.0, firmware for GD32E11x
*/

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  This demo is based on the GD32E113V-EVAL-V1.0 board, it explains how to use the TIMER4 
to calibrate the RTC clock when the IRC40K is used as the RTC clock source.

  Select IRC40K as RTC clock source. And the HyperTerminal should be connected to the 
evaluation board via COM1.

  After start-up, the RTC prescaler is set with the default value (40000). Connect the 
tamper pin (PC13) to an oscilloscope to observe the frequence of RTC second signal.

  Then, press the user key to begin the auto calibration procedure. IRC40K will be connected 
to TIMER4_CH3 input as the source for capture. New prescaler value will be calculated and set.
Related information will be displayed on the HyperTerminal. Connect the tamper pin (PC13) to 
an oscilloscope to observe the new frequence of RTC second signal. At this moment, you can 
find that the frequency of the RTC second signal is more accurate than before.
