[Bitcloud] Using WDT as an interrupt generator

[danergo]

Hello guys

I'm using an ATMEGA256RFR2 and regarding WDT, I stucked in a bit.
I wanted to use the Interrupt mode or the "Interrupt and System Reset Mode". (Datasheet page 218).

Bitcloud has its own WDT functions.
I setup first a callback with HAL_RegisterWdtCallback(afunction);
And then I start the WDT with HAL_StartWdt(WDT_INTERVAL_8000);

In the "afunction" I restart the WDT with HAL_StartWdt(WDT_INTERVAL_8000); again.
This is needed because as per the datasheet, in the Interrupt and System Reset Mode, the first WDT overflow will generate an interrupt, and the second one will reset the IC. But if I set again the WDIE, the next one will also generate the interrupt. And HAL_StartWdt(...) sets this WDIE in the register.

However, my chip keeps restarting itself.

Do you have any idea, what could be the reason of this?

Thank you.

[ataradov]

Do you have any idea, what could be the reason of this?

You start WDT once and for all. In the interrupt you need to call HAL_ResetWdt() to extend the timeout.

[danergo]

It seems the callback is not getting executed.
Does not matter if I call HAL_StartWdt or HAL_ResetWdt in the callback, the chip restart in every 8 seconds.

Registration should be as easy as this, right?
HAL_RegisterWdtCallback(afunction);

Thanks

[ataradov]

It looks like you will actually have to change WDT code. Apparently when WDE bit is enabled in WDTCSR, then reset action is triggered on IRQ exit and manual restart does not help.

[dannyf]

I wanted to use the Interrupt mode or the "Interrupt and System Reset Mode". (Datasheet page 218).

I have never used wdt as a timer on your particular chip but have done similar things on other chips - latest being a lm3s811.

Two words of caution:
1. WDT is a very valuable resource to be wasted on something this trivial. There is no other mechanism on a typical mcu that will trigger a reset with simple passage of time, but plenty of peripherals to measure time.
2. WDT in my view is a terrible timing device. it is generally not accurate and its "in-accuracy" varies with temperature / voltage a lot.

So I would suggest that you do NOT use it for timing purposes.

If you do, maybe coding the registers directly is the way to go.

[Jeroen3]

What is that HAL stuff doing there?
There are literally just 3 bits and a prescaler in a single register.

If you read the manual you'll see that it has many exceptions regarding the use of the WDT.
Your use is not standard. Therefore it will need a non-standard init.
One of them is that you can't clear the WDE when WDRF is true.

If you are in the WDT interrupt, and don't clear the right bits. You chip will reset upon return.