millis() does not return the correct time

My Envitonment

STM32F103(8MHz Xtal) + platformIO

Platform Manager
================
Platform ststm32
--------
Checking platformio/ststm32                   15.2.0                             [Up-to-date]
Checking platformio/toolchain-gccarmnoneeabi  1.70201.0 @ >=1.60301.0,<1.80000.0 [Up-to-date]
Checking platformio/framework-arduinoststm32  4.20100.211028 @ ~4.20100.0        [Up-to-date]
Checking platformio/framework-arduinoststm32-maple 3.10000.201129 @ ~3.10000.0        [Up-to-date]
Checking platformio/tool-stm32duino           1.0.1 @ ~1.0.1                     [Up-to-date]
Checking platformio/tool-openocd              2.1100.211028 @ ~2.1100.0          [Up-to-date]
Checking platformio/tool-dfuutil              1.9.200310 @ ~1.9.190708           [Up-to-date]

My config

[platformio]
default_envs = blackpill_f103c8

[env:blackpill_f103c8]
platform = ststm32
board = blackpill_f103c8
framework = arduino
lib_deps =
  https://github.com/stm32duino/STM32LowPower
  https://github.com/stm32duino/STM32RTC

My code

#include <Arduino.h>
#include "STM32LowPower.h"

void setup() {
  LowPower.begin();
  Serial.begin(115200);
  Serial.println("serial (same as 1)");
  Serial.println("*****");
}

void loop() {
  unsigned long nowMillis = millis();
  Serial.println(nowMillis);
  //Serial.println("serial printing 2");
  //for(int i=0;i<20;i++) LowPower.deepSleep(1000);
  //for(int i=0;i<10;i++) LowPower.sleep(1000);
  for(int i=0;i<10;i++) LowPower.idle(1000);
  //delay(1000);
}

Problem

millis() does not return the correct time.
idle can stop the clock.

Screen Shot

In fact, there is no issue here as when you enter in one of the sleep mode the interrupt are disabled.

STM32LowPower/src/low_power.c

Line 259 in c2e8d13

__disable_irq();

For IDLE mode the systick is simply disabled:

STM32LowPower/src/low_power.c

Lines 234 to 239 in c2e8d13

    
             /* 
        
              * Suspend Tick increment to prevent wakeup by Systick interrupt. 
        
              * Otherwise the Systick interrupt will wake up the device within 
        
              * 1ms (HAL time base) 
        
              */ 
        
             HAL_SuspendTick();

As millis relies on the systick it is normal it is not incremented during the sleep.
You can use the RTC to compensate it if you need.

	/*
	* Suspend Tick increment to prevent wakeup by Systick interrupt.
	* Otherwise the Systick interrupt will wake up the device within
	* 1ms (HAL time base)
	*/
	HAL_SuspendTick();