I have been trying to set 1ppm RTC clock for two days.I have read the datasheet and manual. They are recommended to use 2 timers and an external oscillator. Also, with using HAL_RTCEx_SetSmoothCalib function, says that we can calibrate it easily. I set the RTC routed output as calibration 512Hz, but the frequency of it is 511.96Hz. After that, I read a manual that is CD00167326 for STM32F1s. As it says, I have calculated the ppm error.
512-511.96=0.04Hz => 0.04/511.96=7.81e-5 => ppm=78.13, the manual recommends the using 83 for the calibration value.
And then called the smooth calibration function this value. Thus;
HAL_RTCEx_SetSmoothCalib(&hrtc, RTC_SMOOTHCALIB_PERIOD_32SEC, RTC_SMOOTHCALIB_PLUSPULSES_RESET, 83);
However, although the calibration value has been changed, the routed value is still the 511.96Hz. Why doesn't it change?