Hi Pavel,
> Am 24.10.2016 um 14:34 schrieb Pavel Machek <pa...@ucw.cz>:
>
> Hi!
>
>> On Mon, Feb 22, 2016 at 06:58:13AM +0100, H. Nikolaus Schaller wrote:
>>>>> static inline int fuel_level_LiIon(int mV, int mA, int mOhm) {
>>>>> ...
>>>>> }
>>>
>>> To which header file should this go?
>>
>> I think it should get its own header file in include/linux/power/.
>> Maybe something like "generic-fuel-gauge.h". I'm open to other
>> solutions, though.
>
> I'd like to use use this formula in my own code. Is it somewhere in
> the kernel already?
Not that I am aware of. Marek is still working on the generic-adc-battery
driver augmented by DT + iio-ADC + formula before publication.
Here is the latest draft so you can cherry-pick it into your work:
http://git.goldelico.com/?p=gta04-kernel.git;a=patch;h=22ab047ae296e998379c1aa29fe1210043cfa040
But beware: I think it is quite wrong using the sqrt() function above 19.66%
and doing linear interpolation below.
By using the sqrt() function it has a steepness that goes to infinity when
reaching
19.66% from above. This makes a quite non-realistic curve with a sharp bend at
19.66%
(which is equivalent to 3.756 V).
No real battery I have seen and measured with a coulomb counter has such a
strange
bend at 3.756 V...
IMHO it would be a better approximation to adjust the factors so that e.g. a
realistic
voltage for "empty" (e.g. 3.3 V) is taken as the 0% point where steepness goes
through
the roof.
It should then be something like:
SOC = sqrt((Volt - 3.3 V) / (4.2 V - 3.3 V))
This goes more smoothly between 100% and 0%.
Or we could even use an exponential function with an exponent different from 1/2
(1 being linear interpolation):
SOC = pow((Volt - 3.3 V) / (4.2 V - 3.3 V), factor)
But this would probably need floating point arithmetic in the kernel or some
numeric
approximation algorithm.
BR,
Nikolaus
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