I am trying to clear the IWDG_STDBY bit set in flash so I can enter standby mode without the watchdog timer waking up the MCU.

[CFlec]

I am using an STM32f746zg and this is what I have been trying:

HAL_FLASH_Unlock();

CLEAR_BIT(FLASH->OPTCR, FLASH_OPTCR_IWDG_STDBY);

HAL_FLASH_Lock();

But it doesn't seem to actually modify the bit. What is the proper procedure to clear this bit in flash?

Thanks in advance!!

Charles

[TDK]

Changing option bytes requires you to unlock them, modify them, then activate them by writing to OPTSTRT.

Unlocking flash is different from unlocking option bytes.

Example:

https://github.com/STMicroelectronics/STM32CubeF7/blob/c7c5ec99c7482ea8bcdbf0a869c930af4547088f/Projects/STM32756G_EVAL/Examples/FLASH/FLASH_WriteProtection/Src/main.c

Disabling IWDG requires a chip restart as well, so this scheme won't quite work as is.

[CFlec]

So I've gotten it to clear the bits properly, but they don't seem to persist on reset. I've been resetting by just allowing the watchdog timer to runout, is there a better way to reset?

Thanks again!!

Charles

[TDK]

I can't see what you're doing. Show the code you're using or follow a working example.

[CFlec]

On startup I am trying to check if those bits are cleared, if they aren't I clear them and then force a watchdog reset. Here is my code:

// Check if the watchdog pause on sleep bits are set. If they aren't, set them and reset.

    HAL_FLASH_OB_Unlock();

    HAL_FLASH_Unlock();

    // Read the bits.

    if (FLASH->OPTCR & 0xC0000000)

    {

        printf("Sleep bits are not set.\r\n");

        // Clear the bits.

        CLEAR_BIT(FLASH->OPTCR, FLASH_OPTCR_IWDG_STOP);

        CLEAR_BIT(FLASH->OPTCR, FLASH_OPTCR_IWDG_STDBY);

        // Lock flash.

        HAL_FLASH_OB_Lock();

        HAL_FLASH_Lock();

        // Force a watchdog reset.

        while(1);

    }

It looks like the bits get cleared when I clear them, and then I force a reset as is required for those bits. After the reset the bits seem to get set again, though, so I think I am missing a step.

Thanks!!

Charles

[TDK]

You need to call HAL_FLASH_OB_Launch after changing the option bytes and before locking them in order to apply the changes and to reset the chip.

Again, look at what the example code does:

https://github.com/STMicroelectronics/STM32CubeF7/blob/c7c5ec99c7482ea8bcdbf0a869c930af4547088f/Projects/STM32756G_EVAL/Examples/FLASH/FLASH_WriteProtection/Src/main.c#L133

[CFlec]

Ah, I was calling that after I locked, so it wasn't working. Looks good now, thanks for the help!!

Thanks,

Charles