[This is a reconstruction of a thread I've started on Mar 26, 2017, but got lost in the two forum software transitions since then.]
To find out the real working of IWDG, I took a DISCO-F4, wrote a snippet which brought out LSI through its connection to TIM5_CH4 onto a pin, wired up a LA and started experimenting.
The following is my interpretation of what I've seen; I don't know what's the real implementation of course so I might have misinterpreted things. I haven't experimented with the debug facility. I haven't used other prescaler than the lowest (i.e. /4) - some of the cycles numbers mentioned below might be dependent on this.
As I've said, this is just a guess how things might work, I don't see the innards of the chip.
ST, please comment.
Dear @waclawek.jan ,
Greetings and How are you doing today ? After a long and deep investigation with our experts and design teams that took about 5 days including some public holidays. We confirm all of the findings on IWDG and our action plan is on-going to update and communicate via our official documentation :
thank You very much again for your time and patience , if you need early drafts once we approve them internally @Sarra.S can help .
have a great weekend and many many thanks for the valuable contribution .
Hi @STOne-32 ,
Thanks for letting us know.
> if you need early drafts
Thanks, I don't. I don't use the IWDG, in fact, this was my only "physical" encounter with watchdogs as such so far (although I've written about them in the distant past).
However, what I would very much like to see is an Application Note. I know that means another 5 or more days of work, including FAEs, but I believe it's time and effor well spent. In such AN, I'd like to see a general overview of the topic, including discussion of merits and drawbacks (as they are!) of using WD as such, legislative requirements for its usage; discussion of various forms of WD from hardware single-shots through clocked ones up to complex things like WD-refresh-over-internet; overview of WD implementations in STM32 families; intimate details and relationships such as LSI-autostart-which-does-not; techniques to use IWDG in software and common pitfalls, errors and misconceptions. (Oh, maybe that's not one AN. You may have heard of my "dozens of appnotes per peripheral" mantra...)