[Letux-kernel] Pyra charging

[Michael Mrozek]

Am Donnerstag, den 12.11.2020, 11:50 +0100 schrieb H. Nikolaus 
Schaller:


Hi,

Dave also mentioned something about the Watchdog in IRC, AFAIR, seems
like there's still a lot we can do regarding the driver software.

I also did test a bit more - and found out the following:

* If I charge the unit (while idling) via the Serial port, it draws
about 1.8A (at 5.3V) from my power supply, which seems to work fine.

* If I charge the unit via the USB OTG port, it draws about 2.5A, so it
seems using this port, the battery can be charged faster. However, when
I do this, the battery shows an error after a while. I put the battery
out and measured the temperature using an external measurement device -
and it was around 39°C. So yeah, that's probably the reason here it
disconnects!

It seems with 2.5A, the battery runs too hot, where it works still fine
with 1.8A.

It could be that 45°C would be good enough (if we change the
resistors), but a quick question upfront:

Can we limit the input current?

So, for example, if we had some thermal management that watches the
temperature: If the battery reaches 32°C, limit the current to 2A max
to prevent the battery from heating even more?

Is that limit software configurable - or does the bq not support this?

> I have a new observation. While testing the new mipi display driver
> the battery drained completely and the Pyra was shut down (by
> Palmas).
> 
> Then I connected the charger to the USB port. Charging (and the Pyra)
> started for a short time (LED goes red).
> 
> After a while the Pyra went off again, even with USB cable connected.
> And the red LED turned off. At ca. 30°C. So no over/under
> temperature.
> 
> Now the interesting observation: even unplugging and replugging
> the USB cable did not (re)start charging to let the LED go red.
> 
> What I had to do was to unplug USB and remove the battery. After
> that,
> the Pyra was constantly charging for ca. 4-5 hours until the battery
> became full. Even while I turned on/off/reboot the Pyra while
> continuing
> my tests.
> 
> Now the new idea: does this have something to do with the "safety
> timer?". Should we restart it to trigger a new charging sequence?
> Does it stop every further charging attempt once expired?
> 
> I am not even sure if the safety timer can be reset by software.
> 
> If not, we may have to use the bq2429x watchdog which resets the
> chip (like unplugging the battery) if the OMAP isn't retriggering
> it every now and then. This would also have the benefit that the
> chip falls in a well defined state if we turn the OMAP off which
> does not depend on what the bq driver did in the past minutes.
> 
> I have some (untested/incomplete/experimental) bq2429x watchdog
> extension which I have attached.
> 
> Discussion of this topic is welcome.
> 
> BR,
> Nikolaus
> 
> _______________________________________________
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> Kernel at pyra-handheld.com
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-- 
Mit freundlichen Grüßen,

Michael Mrozek

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