WDT C55x5

Jrvanho

Can someone give me a little more detail on how the WDT works on the C55x5 processors? The app note doesn't really state if you can change any of the values once it is enabled.

Can the prescaler of the WDT be changed once it is enabled? If so, does the counter get reset to the set value? Does the prescaler continue counting down from the old value until it rolls over and then uses the new one?

Cheers!

over 13 years ago

0 Steve Tsang over 13 years ago

TI__Mastermind 23785 points

The WDT countdown would not start if it is only enabled. You can modify the Prescale and Start Value following the lock sequence.

But if the countdown has started via the Kick Register, it is proper to disable the count first before modifying. Then starts the countdown again.

Regards.

0 Jrvanho over 13 years ago in reply to Steve Tsang

Intellectual 730 points

Steve,

Thanks for the quick reply. So if I configure it by setting the Prescale and Start Value, and then enabling it. At random points I unlock and kick the dog. Then while it is counting down, I unlock the Prescale and change it. Does this take effect immediately, on roll over, does it even take effect?

If I have to disable it and re-enable it, doesn't the count get reset and the count down start over when this happens?

Cheers!

0 Steve Tsang over 13 years ago in reply to Jrvanho

TI__Mastermind 23785 points

Changing the value while it is counting down is not a recommended operation.

Yes, the count starts with new value once started.

Regards.

0 Jrvanho over 13 years ago in reply to Steve Tsang

Intellectual 730 points

Steve,

I am trying to use the WDT in the idle state. When I enter the Idle state, I put the PLL in bypass mode. This changes the SysClk from 120 MHz to 32kHz. So my time out goes from 4 seconds to over minutes. I was hoping to change the Prescaler when I disable the PLL and change it back on exit of Idle. Do you have any recommendations for this situation?

Cheers!

0 Steve Tsang over 13 years ago in reply to Jrvanho

TI__Mastermind 23785 points

What about program the value and enable it, only starts it after bypass; stop it upon exit, program a new value and starts it again.

Would this sequence work for you?

Regards.

0 Jrvanho over 13 years ago in reply to Steve Tsang

Intellectual 730 points

I don't think that would make sense.

Say you have a DSP/Bios thread that kicks your WDT that dies. But the idle task keeps running and you keep getting tick interrupts. Because the WDT keeps getting resetting the on idle entry and exit the application will continue to run. This seems to defeat the purpose of the WDT.

Does that make sense?

0 Jrvanho over 13 years ago in reply to Jrvanho

Intellectual 730 points

It might be possible for a totally synchronous application, but since most of them are not you wouldn't be able to set the counter value correctly.

Cheers!

0 Jrvanho over 13 years ago in reply to Jrvanho

Intellectual 730 points

Is it possible to put a feature request for future parts to have the WDT based on the 32kHz clock in?

0 Steve Tsang over 13 years ago in reply to Jrvanho

TI__Mastermind 23785 points

Yes. Sure we welcome customer's inputs to our future product s' feature list.

What about an option to allow the clock source be programmable to use external clock source coming in via GPIO pin?

Regards.

0 Jrvanho over 13 years ago in reply to Steve Tsang

Intellectual 730 points

I think the more options the better. But for the C55x5 parts, I think the 32kHz is a good starting option. External IO would be nice as well.

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WDT C55x5