Is there a way to save a flag or memory location before going to StandBy or StopMode

[Vu.Andy]

Posted on December 06, 2017 at 00:39

Hi,

I was wondering if there is a way to save a few flags or CPU condition before I put the CPU either to SandBy or Stop Mode?

Are there any memory locations that I can write to, then retrieve after woken up from either StandBy or Stop mode?

Thanks,

-Andy

[Andrew Neil]

Posted on December 06, 2017 at 01:56

RTC backup registers?

EEPROM Emulation?

[Vu.Andy]

Posted on December 06, 2017 at 02:18

Thank you.  I think RTC backup registers are my best option.

[Vu.Andy]

Posted on December 06, 2017 at 20:02

I've run in a bit of a potential problem.  In order to use the RTC backup register, I have to execute this function

at the beginning of the program to select the RTC clock source:

HAL_RCCEx_PeriphCLKConfig();

But based on the STM documentation, if this function is executed, all the RTC backup registers are reset to their default

state, which does present a problem.

After the the uProcessor has woken up from StandBy Mode, I assume I have to initialize all my clock, INCLUDING

the RTC clock which means I have to execute this function: HAL_RCCEx_PeriphCLKConfig().  But if I execute

this function, then all the value in the RTC registers are lost.

So could you provide some feeback how to resolve this issue?

Thanks.

[Tesla DeLorean]

Posted on December 06, 2017 at 21:50

Just enable the clocks in the PWR domain, and unlock the PWR/RTC.

  /* Enable the PWR clock */

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);

  /* Allow access to Backup Domain */

  PWR_BackupAccessCmd(ENABLE);

Some of the parts also have 4KB of BKPRAM

In the SPL this is done to get the RTC working, and not stomp on everything if starting via STANDBY

STM32F0xx_StdPeriph_Lib_V1.5.0\Projects\STM32F0xx_StdPeriph_Examples\PWR\PWR_Standby\main.c

static void RTC_Config(void)

{

  RTC_InitTypeDef   RTC_InitStructure;

  RTC_TimeTypeDef   RTC_TimeStructure;

  uint32_t LSIFreq = 0;

  /* Enable the PWR clock */

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);

  /* Allow access to Backup Domain */

  PWR_BackupAccessCmd(ENABLE);

  /* Disable wake-up source(ALARM) to guarantee free access to WUT level-OR input */

  RTC_ITConfig(RTC_IT_ALRA, DISABLE);

  /* Clear Wakeup flag */

  PWR_ClearFlag(PWR_FLAG_WU);

  /* Enable wake-up source(ALARM) to guarantee free access to WUT level-OR input */

  RTC_ITConfig(RTC_IT_ALRA, ENABLE);

  /* Enable the LSI OSC */

  RCC_LSICmd(ENABLE);

  /* Wait till LSI is ready */

  while (RCC_GetFlagStatus(RCC_FLAG_LSIRDY) == RESET)

  {}

  /* Check if the StandBy flag is set */

  if (PWR_GetFlagStatus(PWR_FLAG_SB) != RESET)

  {

    /* Clear StandBy flag */

    PWR_ClearFlag(PWR_FLAG_SB);

    /* Check if the StandBy flag is cleared */

    if (PWR_GetFlagStatus(PWR_FLAG_SB) != RESET)

    {

      while(1);

    }

    RTC_WaitForSynchro();

    /* No need to configure the RTC as the RTC config(clock source, enable,

    prescaler,...) are kept after wake-up from STANDBY */

  }

  else

  {

    /* RTC Configuration ******************************************************/

    /* Reset Backup Domain */

    RCC_BackupResetCmd(ENABLE);

    RCC_BackupResetCmd(DISABLE);

    /* Select the RTC Clock Source */

    RCC_RTCCLKConfig(RCC_RTCCLKSource_LSI);

    /* Enable the RTC Clock */

    RCC_RTCCLKCmd(ENABLE);

    /* Wait for RTC APB registers synchronisation */

    RTC_WaitForSynchro();

    /* Get the LSI frequency:  TIM14 is used to measure the LSI frequency */

    LSIFreq = GetLSIFrequency();

    RTC_InitStructure.RTC_HourFormat = RTC_HourFormat_24;

    RTC_InitStructure.RTC_AsynchPrediv = 99;

    RTC_InitStructure.RTC_SynchPrediv =  (LSIFreq/100) - 1;

    RTC_Init(&RTC_InitStructure);

    /* Set the time to 01h 00mn 00s AM */

    RTC_TimeStructure.RTC_H12     = RTC_H12_AM;

    RTC_TimeStructure.RTC_Hours   = 0x01;

    RTC_TimeStructure.RTC_Minutes = 0x00;

    RTC_TimeStructure.RTC_Seconds = 0x00;

    RTC_SetTime(RTC_Format_BIN, &RTC_TimeStructure);

  }

}

[Vu.Andy]

Posted on December 11, 2017 at 23:19

Hi Clive,

Thanks for the info very much.  Here is what I plan to do, could you comment if this is correct?

I am trying to preserve the HAL structure as much as possible and do not change too much.  Thanks.

The function used to setup RTC is : HAL_RCCEx_PeriphCLKConfig(RCC_PeriphCLKInitTypeDef  *PeriphClkInit)

Within this function, it checks to see if the RTC clock is selected:

if(((PeriphClkInit->PeriphClockSelection) & RCC_PERIPHCLK_RTC) == (RCC_PERIPHCLK_RTC))

{

}

If RCC_PERIPHCLK_RTC is not part of the RCC_PeriphCLKInitTypeDef, then it will not initialize the RTC clock.

So, in the main(), I would check if the uController was from a reset state,

then go ahead and initialize the RTC.

   

if (__HAL_RCC_GET_FLAG(RCC_FLAG_IWDGRST) == RESET)

   PeriphClkInit.RTCClockSelection = RCC_RTCCLKSOURCE_LSI;

  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)

  {

_Error_Handler(__FILE__, __LINE__);

  }

But if the uController was from a StandBy wake up mode, then just enable the Power clock and allow access to RTC:

if (__HAL_RCC_GET_FLAG(RCC_FLAG_IWDGRST) != RESET)

{

     /* Enable Power Clock*/

  __HAL_RCC_PWR_CLK_ENABLE();       

  /* Allow access to Backup */

   HAL_PWR_EnableBkUpAccess(); 

}