[stm32u585] HAL_IWDG_Init reconfig does not take effect

[lll]

hello,

I encountered a problem while developing for stm32u585.

I change the iwdg reload value by HAL_IWDG_Init(), and then HAL_PWR_EnterSTANDBYMode(), but the new reload value does not take effect:

    hiwdg.Instance = IWDG;
    hiwdg.Init.Prescaler = IWDG_PRESCALER_64;
    hiwdg.Init.Window = 4095;
    hiwdg.Init.Reload = 3600;
    hiwdg.Init.EWI = 0;
    HAL_IWDG_Init(&hiwdg);
    HAL_IWDG_Refresh(&hiwdg);
    HAL_Delay(300);  //more than one downcount
    HAL_PWR_EnterSTANDBYMode();

if delay before refresh, it seems work

    hiwdg.Instance = IWDG;
    hiwdg.Init.Prescaler = IWDG_PRESCALER_64;
    hiwdg.Init.Window = 4095;
    hiwdg.Init.Reload = 3600;
    hiwdg.Init.EWI = 0;
    HAL_IWDG_Init(&hiwdg);
    HAL_Delay(300);  //more than one downcount
    HAL_IWDG_Refresh(&hiwdg);
    HAL_PWR_EnterSTANDBYMode();

Is this the correct process ? If I want to ensure the modification is successful, what should I pay attention to

[Saket_Om · Accepted solution]

Hello @lll 

after changing the IWDG prescaler/reload, the new configuration is not guaranteed to be fully effective if you enter STANDBY immediately. Even though HAL_IWDG_Init() waits for update flags, the IWDG (running on LSI in another clock domain) needs a short time to synchronize internally. Therefore, your second sequence is the correct approach: add a small delay after HAL_IWDG_Init() and before the first HAL_IWDG_Refresh() / HAL_PWR_EnterSTANDBYMode(), to ensure the new reload value is properly taken into account.

[lll]

LSI=32K, prescaler=128 ==> IWDG=250Hz

before: prescaler=64, reload=40

after: prescaler=512, reload=3600

if i only config once, i need to delay about 3s. if i config twice, it seems that only a delay of 300ms is needed:

    hiwdg.Instance = IWDG;
    hiwdg.Init.Prescaler = IWDG_PRESCALER_64;
    hiwdg.Init.Window = 4095;
    hiwdg.Init.Reload = 3600;
    hiwdg.Init.EWI = 0;
    HAL_IWDG_Init(&hiwdg);
    HAL_Delay(350);
    HAL_IWDG_Refresh(&hiwdg);

    hiwdg.Instance = IWDG;
    hiwdg.Init.Prescaler = IWDG_PRESCALER_512;
    hiwdg.Init.Window = 4095;
    hiwdg.Init.Reload = 3600;
    hiwdg.Init.EWI = 0;
    HAL_IWDG_Init(&hiwdg);

is this sequence correct?