STM32F103C8T6 RTC losing about one second on each system reset. #66
Description
I'm using the RTC of a Bluepill STM32F103C8T6. It has a supercap on VBat. The installed version of the STM32duino rtc library is 1.2.0.
The STM32 Arduino Core is at version 2.2.0.
If I press the reset button on the Bluepill, the RTC appears to lose about 1 second on each press.
I am using the following code based on this example to demonstrate this problem: https://github.com/stm32duino/STM32RTC/blob/main/examples/SimpleRTC/SimpleRTC.ino
/* SimpleRTC This sketch shows how to configure the RTC and to display the date and time periodically Creation 12 Dec 2017 by Wi6Labs Modified 03 Jul 2020 by Frederic Pillon for STMicroelectronics This example code is in the public domain. https://github.com/stm32duino/STM32RTC */ #include <STM32RTC.h> /* Get the rtc object */ STM32RTC& rtc = STM32RTC::getInstance(); /* Change these values to set the current initial time */ const byte seconds = 0; const byte minutes = 53; const byte hours = 12; /* Change these values to set the current initial date */ const byte weekDay = 1; const byte day = 22; const byte month = 5; const byte year = 22; void setup() { Serial.begin(115200); pinMode(PB12, INPUT_PULLUP ) ; // Select RTC clock source: LSI_CLOCK, LSE_CLOCK or HSE_CLOCK. // By default the LSI is selected as source. rtc.setClockSource(STM32RTC::LSE_CLOCK); rtc.begin(); // initialize RTC 24H format } void loop() { if ( ! digitalRead(PB12) ) { // Set the time rtc.setHours(hours); rtc.setMinutes(minutes); rtc.setSeconds(seconds); // Set the date rtc.setWeekDay(weekDay); rtc.setDay(day); rtc.setMonth(month); rtc.setYear(year); Serial.println( "reset time" ) ; delay( 100 ) ; } // Print date... Serial.printf("%02d/%02d/%02d ", rtc.getDay(), rtc.getMonth(), rtc.getYear()); // ...and time Serial.printf("%02d:%02d:%02d.%03d\n", rtc.getHours(), rtc.getMinutes(), rtc.getSeconds(), rtc.getSubSeconds()); delay(1000); } I have set the clock and taken a series of screen shots and have logged the results. The result is that the delta between local (PC) time and the Bluepill RTC time increases by about one second for each reset. These seconds are just lost.
local time rtc time delta (seconds) 12.57.05 12:53:47 198s 13:00:39 12:57:21 198s 13:03:08 12:59:49 199s 13:13:09 13:09:51 198s 13:18:35 13:15:16 199s 3 X reset here 13:22:16 13:18:55 201s 13:26:16 13:22:55 201s 13:29:21 13:26:00 201s 5 x reset here 13:35:49 13:32:24 205s 13:38:58 13:35:33 205s As can be seen, the delta increases after each series of resets.
This appears similar to this case:
https://community.st.com/s/question/0D50X00009XkgBWSAZ/stm32-rtc-loses-one-second-after-each-reset