From: "H. Nikolaus Schaller" <hns@goldelico.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sre@kernel.org>,
pali.rohar@gmail.com, kernel list <linux-kernel@vger.kernel.org>,
ivo.g.dimitrov.75@gmail.com, patrikbachan@gmail.com,
serge@hallyn.com, abcloriens@gmail.com,
Belisko Marek <marek.belisko@gmail.com>,
Linux PM mailing list <linux-pm@vger.kernel.org>
Subject: Re: generic-adc-battery volatge-to-percent formula
Date: Mon, 24 Oct 2016 15:09:26 +0200 [thread overview]
Message-ID: <3F9199B6-233E-4260-9362-498FB1AA3FB7@goldelico.com> (raw)
In-Reply-To: <20161024123404.GA24185@amd>
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Hi Pavel,
> Am 24.10.2016 um 14:34 schrieb Pavel Machek <pavel@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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next prev parent reply other threads:[~2016-10-24 13:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAAfyv37rjchL=FtvgGhjrfXnCvhfbYCext48QmSuOgJ5RjTwAQ@mail.gmail.com>
[not found] ` <20160212085157.GA16326@amd>
[not found] ` <CAAfyv34=C5NSTuqR9Pf4MT2Z42XvT_1Gw+kyjZZh12zC2cBoFA@mail.gmail.com>
[not found] ` <20160215115304.GA5014@amd>
[not found] ` <20160221200653.GD15242@earth>
[not found] ` <0BD7A329-A8BE-4B3E-B98F-CAB7A25F643F@goldelico.com>
[not found] ` <20160221211257.GA26418@amd>
[not found] ` <7720041C-DFEC-4592-A5AE-0C2BEEFB6049@goldelico.com>
[not found] ` <20160222172009.GA7393@earth>
2016-10-24 12:34 ` generic-adc-battery volatge-to-percent formula Pavel Machek
2016-10-24 13:09 ` H. Nikolaus Schaller [this message]
2017-04-11 17:31 ` Pavel Machek
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