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adaptable soft power limit with backoff (mostly S60, useful for very-low-ohm tip like JBCs on USB PD) #1801

Description

@jakobi

I would like to request a "soft power limit backoff on recent PD/QC resets":

Defaulting to off, or VALUE in WATTs. This feature should catch very recent PD resets due too-fast-switching or too-high-currents, and in this case lower the "soft power limit" in multiple steps down to say a lower sanity boundary of 20W.

The temporary soft limit should be kept until the tip is changed. A boot up without seeing any "recent reset" should change the value back to off (or the already existing hard power limit, which should take precedence if lower :)).

Alternative implementations: boolean to control backoff, and add the behaviour to the current power limit code, with a hard limit in flash and a current in ram.

Advantage: When switching to "friendly tips", power limit is off, when switching to tips where pwm is "too aggressive for the capricious charger", we get a reset or two, and the tip heats up with a temporary lower power limit. So no fiddling with the current power limit settings for proplematic tips.

Note that the notion of "recent" might be problematic, and sometimes the reset is immediate so that the tip is still cool to the touch, thus a hot tip is not sufficient for 'recent' (and unplugging/replugging with a hot tip should not trigger the "soft power limit backoff" either).

Use case / current situation with just a hard power limit:

This was tested with the 1.22 prerelease on s60 and a cranky baseus 120w pd/qc charger, supporting 12V/3A.

I have 2 tips working somewhat nicely (only one reset at low temp, recover+reheat and we reach solder temps).

3 more tips making the baseus reset without power limit, and even some downto a limit of 35W (ironos).

With a power limit of 25W in ironos 1.22, finally all tips heatup (slowly).

The behaviour doesn't seem to relate to clone tip vs JBC. And only my 2nd Baseus PD-charger-with-powerbank is more lenient and thus suffers somewhat less resets.

Still with the original firmware, I played with its "power percentage" setting, but I never noticed an effect, like e.g. a reduced number of resets during heatup.

PS: A very subjective impression, lacking a proper stop watch setup: original 1.11 firmware seems more aggressive/faster (both firmwares without power limits). But the original seems to round/dejitter over short periods to "better" display a temperature... . Not that I can revisit this lacking the hex of the original firmware :).

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