[Letux-kernel] Pyra charging

Tue Nov 17 17:55:31 CET 2020

Just had the phenomenon again after ca. 2 days of test runs (poweroff, reflash SD card, reboot, tests).

No reaction to unplugging/replugging the USB cables.
Or pressing the power button. Pyra was dead.
Even when connected to USB and removing/reinserting battery.

The Pyra started operation only after first removing/inserting battery (with USB connected) and un/replugging USB.

bq24721 tells:

capacity: 1%
status: Charging
level: Low
volt: 3193000uV
current: 85000uA
temp: 31.6°C
charge: 20000uAh
full: 5441000uAh
design: 6000000uAh

So my favourite explanation is the safety timer in the bq24297 which is not being reset
and stops any charging attempt. It is only reset by battery removal.

Or charging does not automatically restart if charge level goes below e.g. 80%. So if
connected to a weak USB the battery will go to "supplemental mode" but will not be recharged.

BR,
Nikolaus

> Am 12.11.2020 um 17:10 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> 
>> Am 12.11.2020 um 16:37 schrieb Michael Mrozek <EvilDragon at openpandora.org>:
>> 
>> Am Donnerstag, den 12.11.2020, 11:50 +0100 schrieb H. Nikolaus 
>> Schaller:
>> 
>> 
>> Hi,
>> 
>> Dave also mentioned something about the Watchdog in IRC,
> 
> I think he meant the Palmas WDT. There are 3 different ones!
> bq24297, palmas, omap5.
> 
> bq24297-wdt: for resetting the bq to default charging if OMAP is off or panics
> palmas-wdt: could turn of OMAP power if OMAP panics
> omap5-wdt: generates an interrupt and warning and may kernel panic
> 
>> AFAIR, seems
>> like there's still a lot we can do regarding the driver software.
> 
> Yes.
> 
>> 
>> 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.
> 
> Sure, less charging current means less heat to dissipate. Basically the
> battery is a capacitor and a resistor. The resistor generates heat according
> to P = I^2 / R. So doubling the current means four times heat.
> 
>> 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?
> 
> Yes. You can always do
> 
> 	echo 2000000 >/sys/class/power_supply/bq24297/input_current_limit
> 
> (or similar, I do not remember the exact path).
> 
> BTW: on my rootfs setups it is limited to 2A so I should not be able to
> measure 2.5A.
> 
>> 
>> 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?
> 
> Yes, that is a good idea. It would extend charging time but is a
> control knob to turn...
> 
>> 
>> Is that limit software configurable - or does the bq not support this?
> 
> Yes it does. Not continuously but AFAIR there are ca. 8 levels.
> 
>> 
>>> 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
>>> 
>>> _______________________________________________
>>> Kernel mailing list
>>> Kernel at pyra-handheld.com
>>> http://pyra-handheld.com/cgi-bin/mailman/listinfo/kernel
>> 
>> -- 
>> Mit freundlichen Grüßen,
>> 
>> Michael Mrozek
>> 
>> -----------------------
>> OpenPandora GmbH
>> Geschäftsführer: Michael Mrozek
>> 
>> Schäffbräustr. 11
>> 85049 Ingolstadt
>> Deutschland
>> Tel.: 0841 / 990 5548
>> http://www.openpandora.de/
>> HRB 4879, Amtsgericht Ingolstadt
>> -----------------------
>> eMail: mrozek at openpandora.org
> 