Watchdog - stop iwdg counter in deepsleep (STOP mode)

[JeroenIoT]

Hi,

Have been playing with the IWatchdog and the basics are working fine.
What I want to do is the freeze the IWDG counter while in lowpower deepsleep.

I have tried the code below to freeze the counter, however it continues to reset while in deepsleep

  __HAL_RCC_DBGMCU_CLK_ENABLE();
  __HAL_DBGMCU_FREEZE_IWDG();
  IWatchdog.begin(IWDG_TIMEOUT_MAX); // approx 28 seconds in my hw setup
  lp.deepSleep();                     // lowPower lib

I verified the register (DBG_IWDG_STOP at 0x4001 5808 and bit 12 is set to 1. So imho the IWDG should be frozen when in STOP mode.
What am I missing?

Chrs

[fpistm]

Hi,
I don't think you can stop it.
The __HAL_DBGMCU_FREEZE_IWDG() is used when the device enters Debug Mode (core halted) not in a low power mode.

As stated by the ref man:
Once running, the IWDG cannot be stopped.

The only way I can see is to wakeup the mcu before the iwdg expiration to reset it.

[JeroenIoT]

Thanks

Maybe you are right. I know it cannot be stopped but hoping that it was possible to freeze the IWDG counter.
Rewriting the LowPower deepsleep to wakeup e.g. every 20 seconds to reload the IWDG is not preferred :-)

I will deepdive into this during the weekend. Post my feedback later on

[fpistm]

You can freeze it the cpu is halted not in a low power mode.

[JeroenIoT]

My understanding is that it can be halted when in stop mode.

I am a bit confused about when I actually place the mcu in stop mode and what mode I am in when placing it in deep sleep.
For me I would like to "do nothing" and wake up by an RTC alarm or by an external interrupt

[fpistm]

IWDG will not stop or freeze during low power mode. You may try to reset the mcu then after restart enter in low power without start the IWDG.

[JeroenIoT]

@fpistm - I checked the ST ref docs over the weekend and freezing the IWDG downcounter indeed seems not possible for the STM32L082. I quickly tested:

1> Go to lowpower deepsleep for 20 seconds
2> Reload IWDG counter
3> Goto step 1 untill you slept enough

Testing the above results in an increase of approx. 1.5uA compared to not waking up to reload the IWDG
(just sharing to whomever might have same situation )

[LMESTM]

Note: The IWDG is also useful in this case to make sure you won't get stuck in sleep mode forever.
I don't know if you can change the IWDG period though

[fpistm]

Note: The IWDG is also useful in this case to make sure you won't get stuck in sleep mode forever. I don't know if you can change the IWDG period though

Right, as stated in the README.md here:
https://github.com/stm32duino/Arduino_Core_STM32/tree/main/libraries/IWatchdog

Valid timeout values depends of the LSI clock. Typically, it is 32kH value are between
125µs and 32,768ms (~32.8 seconds). The precision depends of the timeout values:

timeout value range	timeout value precision
125µs - 512ms	125µs
513ms - 1024ms	250µs
1025ms - 2048ms	500µs
2049ms - 4096ms	1ms
4097ms - 8192ms	2ms
8193ms - 16384ms	4ms
16385ms - 32768ms	8ms

[JeroenIoT]

The timeout values above are related to WWDG
The IWDG time is "sort of" configurable up to 28 secs (afaik).
See 24.3.1 in [RefManual] (https://www.st.com/resource/en/reference_manual/rm0376-ultralowpower-stm32l0x2-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

[fpistm]

Yes in the case of L0x2 as the LSI is 37kHz with a prescaler of 256 for a 12 bits counter the max value is 28.33s.
Example above is (as stated) for a LSI of 32KHz 😉