* Pavel Machek [off-list ref] [210219 21:58]:

quoted

quoted

If I turn off charging with echo 0 > input_current_limit, 0.2 to 0.4A
is drawn from USB, and battery is not discharged:

root@devuan-droid4:/sys/class/power_supply/usb# echo 0 >  input_current_limit
root@devuan-droid4:/sys/class/power_supply/usb# cat current_now
0

Hmm so have you measured that setting the current limit to 0 actually
draws something from the USB?

Yes, it does, if I do the echo when charge is done. (I have small USB
passthrough with volt and amp meters). It has been behaving weirdly in
other cases.p

OK great, seems like we can just change the charger timeout then.

quoted

I recall clearing the ichrgr bits stops the vbus draw completely, but
I could be wrong.

quoted

Is that a better way to handle full battery?

We could experiment with switching over to usb power when the battery is
full. Looking at the docs for mc1378 it might be possible that setting
CPCAP_REG_CRM_FET_OVRD and clearing CPCAP_REG_CRM_FET_CTRL after the
battery is full disables charging but still keep drawing power from
the usb. I'd assume the current limit still needs to be nonzero there
too? Totally untested..

I may be able to test patches...

Yeah this too might be worth testing on some donor device..

quoted

And switching back to battery power on usb disconnect will potentially
only give us very little time based on the different line length for
vbus and ground pins compared to data pins on the usb connector.. And
uvos had some concerns about the battery capacity putting it back online,
so adding him to Cc also.

You mean, we'd have to take interrupt and switch registers in order to
switch back to battery power, and system would crash if we did not
make it in time?

Yes hopefully we don't need to do that. My guess is we should find some
FET_OVRD and FET_CTRL setting we can always keep enabled after charger
negotation. Maybe we already have the right settings based on your tests :)

Regards,

Tony



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