topic Re: Watchdog timeout calculation in Kinetis Microcontrollers

Watchdog timeout calculation

Oleksii — Tue, 24 Nov 2020 18:04:33 GMT

I`m a newbie. Working with MK20DN512VLK10. Please, advice the formula for the watchdog timeout calculation. If possible, to have seconds. Plan to use LPO clock.

Thank you very much. My first project.

Re: Watchdog timeout calculation

mjbcswitzerland — Tue, 24 Nov 2020 21:07:26 GMT

For your device and the watchdog clocked from LPO:

// Watchdog enable and configure macro
//
#define ENABLE_WATCHDOG_TIMEOUT_SECONDS(time) \
UNLOCK_WDOG();\
WDOG_TOVALL = (time * 1000/5);\
WDOG_TOVALH = 0;\
WDOG_STCTRLH = (WDOG_STCTRLH_STNDBYEN | WDOG_STCTRLH_WAITEN | WDOG_STCTRLH_STOPEN | WDOG_STCTRLH_WDOGEN)

In code use this for 1 second timeout

ENABLE_WATCHDOG_TIMEOUT_SECONDS(1); // watchdog enabled to generate reset on 1s timeout (no further updates allowed)

From open source uTasker project with Kinetis simulation - for faster learning and faster developments at https://github.com/uTasker/uTasker-Kinetis

Regards

Mark
[uTasker project developer for Kinetis and i.MX RT]
Contact me by personal message or on the uTasker web site to discuss professional training, solutions to problems or product development requirements

Re: Watchdog timeout calculation

Oleksii — Tue, 24 Nov 2020 21:27:00 GMT

Hi Mark, thank you very much for the reply. Can I ask you to clarify why do we need devision by 5 in WDOG_TOVALL = (time * 1000/5).
Just want to be fully aware of the logic.

Thank you.

Re: Watchdog timeout calculation

Oleksii — Tue, 24 Nov 2020 21:44:33 GMT

Hi Mark, thank you very much for the reply.

Can I ask you to clarify why do we need devision by 5 in WDOG_TOVALL = (time * 1000/5).

Just want to be fully aware of the logic.

Thank you.

Re: Watchdog timeout calculation

mjbcswitzerland — Tue, 24 Nov 2020 22:11:02 GMT

There is a 3 bit pre-scaler which defaults to 4 (divide by 5) and so the time is correct without needing to also adjust this when the 5 is taken into account.

Notice that the macro sets the most significant half word of the compare register to 0 since it already works for up to 320s and greater values would only be of use when the bus clock were used instead. Typically a couple seconds are used for the watchdog timeout.

Regards

Re: Watchdog timeout calculation

Oleksii — Tue, 24 Nov 2020 22:20:45 GMT

Thank you very much for the detailed explanation.